draft-ietf-mboned-mtrace-v2-08.txt   draft-ietf-mboned-mtrace-v2-09.txt 
MBONED Working Group H. Asaeda MBONED Working Group H. Asaeda
Internet-Draft Keio University Internet-Draft NICT
Intended status: Standards Track T. Jinmei Intended status: Standards Track W. Lee, Ed.
Expires: July 11, 2011 ISC Expires: April 25, 2013 Juniper Networks, Inc.
W. Fenner October 22, 2012
Arastra, Inc.
S. Casner
Packet Design, Inc.
January 7, 2011
Mtrace Version 2: Traceroute Facility for IP Multicast Mtrace Version 2: Traceroute Facility for IP Multicast
draft-ietf-mboned-mtrace-v2-08 draft-ietf-mboned-mtrace-v2-09
Abstract Abstract
This document describes the IP multicast traceroute facility. Unlike This document describes the IP multicast traceroute facility, named
unicast traceroute, multicast traceroute requires special Mtrace version 2 (Mtrace2). Unlike unicast traceroute, Mtrace2
implementations on the part of routers. This specification describes requires special implementations on the part of routers. This
the required functionality in multicast routers, as well as how specification describes the required functionality in multicast
management applications can use the router functionality. routers, as well as how an Mtrace2 client invokes a query and
receives a reply.
Status of this Memo Status of this Memo
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 6
4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 10 3. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 10 3.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 8
4.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 10 3.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 8
5. Mtrace2 Query Header . . . . . . . . . . . . . . . . . . . . . 12 3.2.1. Mtrace2 Query . . . . . . . . . . . . . . . . . . . . 9
5.1. # hops: 8 bits . . . . . . . . . . . . . . . . . . . . . . 12 3.2.2. Mtrace2 Extended Query Block . . . . . . . . . . . . . 10
5.2. Multicast Address . . . . . . . . . . . . . . . . . . . . 13 3.2.3. Mtrace2 Request . . . . . . . . . . . . . . . . . . . 11
5.3. Source Address . . . . . . . . . . . . . . . . . . . . . . 13 3.2.4. Mtrace2 Reply . . . . . . . . . . . . . . . . . . . . 11
5.4. Mtrace2 Client Address . . . . . . . . . . . . . . . . . . 13 3.2.5. IPv4 Mtrace2 Standard Response Block . . . . . . . . . 12
5.5. Query ID: 16 bits . . . . . . . . . . . . . . . . . . . . 13 3.2.6. IPv6 Mtrace2 Standard Response Block . . . . . . . . . 16
5.6. Client Port # . . . . . . . . . . . . . . . . . . . . . . 13 3.2.7. Mtrace2 Augmented Response Block . . . . . . . . . . . 19
6. IPv4 Mtrace2 Standard Response Block . . . . . . . . . . . . . 14 4. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 20
6.1. MBZ: 8 bit . . . . . . . . . . . . . . . . . . . . . . . . 14 4.1. Receiving Mtrace2 Query . . . . . . . . . . . . . . . . . 20
6.2. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 14 4.1.1. Query Packet Verification . . . . . . . . . . . . . . 20
6.3. Incoming Interface Address: 32 bits . . . . . . . . . . . 15 4.1.2. Query Normal Processing . . . . . . . . . . . . . . . 21
6.4. Outgoing Interface Address: 32 bits . . . . . . . . . . . 15 4.2. Receiving Mtrace2 Request . . . . . . . . . . . . . . . . 21
6.5. Previous-Hop Router Address: 32 bits . . . . . . . . . . . 15 4.2.1. Request Packet Verification . . . . . . . . . . . . . 21
6.6. Input packet count on incoming interface: 64 bits . . . . 15 4.2.2. Request Normal Processing . . . . . . . . . . . . . . 22
6.7. Output packet count on outgoing interface: 64 bits . . . . 16 4.3. Forwarding Mtrace2 Request . . . . . . . . . . . . . . . . 23
6.8. Total number of packets for this source-group pair: 64 4.3.1. Destination Address . . . . . . . . . . . . . . . . . 24
bits . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4.3.2. Source Address . . . . . . . . . . . . . . . . . . . . 24
6.9. Rtg Protocol: 16 bits . . . . . . . . . . . . . . . . . . 16 4.3.3. Appending Standard Response Block . . . . . . . . . . 24
6.10. Multicast Rtg Protocol: 16 bits . . . . . . . . . . . . . 16 4.4. Sending Mtrace2 Reply . . . . . . . . . . . . . . . . . . 24
6.11. Fwd TTL: 8 bits . . . . . . . . . . . . . . . . . . . . . 16 4.4.1. Destination Address . . . . . . . . . . . . . . . . . 25
6.12. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 16 4.4.2. Source Address . . . . . . . . . . . . . . . . . . . . 25
6.13. Src Mask: 7 bits . . . . . . . . . . . . . . . . . . . . . 17 4.4.3. Appending Standard Response Block . . . . . . . . . . 25
6.14. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 17 4.5. Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . . 25
7. IPv6 Mtrace2 Standard Response Block . . . . . . . . . . . . . 19 4.6. Hiding Information . . . . . . . . . . . . . . . . . . . . 26
7.1. MBZ: 8 bit . . . . . . . . . . . . . . . . . . . . . . . . 19 5. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 26
7.2. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 20 5.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 26
7.3. Incoming Interface ID: 32 bits . . . . . . . . . . . . . . 20 5.1.1. Destination Address . . . . . . . . . . . . . . . . . 26
7.4. Outgoing Interface ID: 32 bits . . . . . . . . . . . . . . 20 5.1.2. Source Address . . . . . . . . . . . . . . . . . . . . 26
7.5. Local Address . . . . . . . . . . . . . . . . . . . . . . 20 5.2. Determining the Path . . . . . . . . . . . . . . . . . . . 26
7.6. Remote Address . . . . . . . . . . . . . . . . . . . . . . 20 5.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 27
7.7. Input packet count on incoming interface . . . . . . . . . 20 5.4. Last Hop Router (LHR) . . . . . . . . . . . . . . . . . . 27
7.8. Output packet count on outgoing interface . . . . . . . . 21 5.5. First Hop Router (FHR) . . . . . . . . . . . . . . . . . . 27
7.9. Total number of packets for this source-group pair . . . . 21 5.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 27
7.10. Rtg Protocol: 16 bits . . . . . . . . . . . . . . . . . . 21 5.7. Non-Supported Router . . . . . . . . . . . . . . . . . . . 28
7.11. Multicast Rtg Protocol: 16 bits . . . . . . . . . . . . . 21 5.8. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 28
7.12. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 21 5.8.1. Arriving at Source . . . . . . . . . . . . . . . . . . 28
7.13. Src Prefix Len: 8 bits . . . . . . . . . . . . . . . . . . 21 5.8.2. Fatal Error . . . . . . . . . . . . . . . . . . . . . 28
7.14. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 21 5.8.3. No Upstream Router . . . . . . . . . . . . . . . . . . 28
8. Mtrace2 Augmented Response Block . . . . . . . . . . . . . . . 22 5.8.4. Reply Timeout . . . . . . . . . . . . . . . . . . . . 28
9. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 23 5.9. Continuing after an Error . . . . . . . . . . . . . . . . 28
9.1. Receiving Mtrace2 Query . . . . . . . . . . . . . . . . . 23 6. Protocol-Specific Considerations . . . . . . . . . . . . . . . 29
9.1.1. Packet Verification . . . . . . . . . . . . . . . . . 23 6.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9.1.2. Normal Processing . . . . . . . . . . . . . . . . . . 23 6.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 29
9.1.3. Mtrace2 Query Received by Non-Supported Router . . . . 23 6.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.2. Receiving Mtrace2 Request . . . . . . . . . . . . . . . . 24 6.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 30
9.2.1. Packet Verification . . . . . . . . . . . . . . . . . 24 7. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 30
9.2.2. Normal Processing . . . . . . . . . . . . . . . . . . 24 7.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 30
9.2.3. Mtrace2 Request Received by Non-Supported Router . . . 26 7.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 30
9.3. Forwarding Mtrace2 Request . . . . . . . . . . . . . . . . 26 7.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 30
9.3.1. Destination Address . . . . . . . . . . . . . . . . . 26 7.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 31
9.3.2. Source Address . . . . . . . . . . . . . . . . . . . . 26 7.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 31
9.4. Sending Mtrace2 Reply . . . . . . . . . . . . . . . . . . 27 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
9.4.1. Destination Address . . . . . . . . . . . . . . . . . 27 8.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 32
9.4.2. Source Address . . . . . . . . . . . . . . . . . . . . 27 8.2. UDP Destination Port . . . . . . . . . . . . . . . . . . . 32
9.5. Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . . 27 9. Security Considerations . . . . . . . . . . . . . . . . . . . 32
9.6. Hiding Information . . . . . . . . . . . . . . . . . . . . 28 9.1. Addresses in Mtrace2 Header . . . . . . . . . . . . . . . 32
10. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 29 9.2. Topology Discovery . . . . . . . . . . . . . . . . . . . . 32
10.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 29 9.3. Characteristics of Multicast Channel . . . . . . . . . . . 32
10.1.1. Destination Address . . . . . . . . . . . . . . . . . 29 9.4. Limiting Query/Request Rates . . . . . . . . . . . . . . . 33
10.1.2. Source Address . . . . . . . . . . . . . . . . . . . . 29 9.5. Limiting Reply Rates . . . . . . . . . . . . . . . . . . . 33
10.2. Determining the Path . . . . . . . . . . . . . . . . . . . 29 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33
10.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 29 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.4. Last Hop Router . . . . . . . . . . . . . . . . . . . . . 29 11.1. Normative References . . . . . . . . . . . . . . . . . . . 33
10.5. First Hop Router . . . . . . . . . . . . . . . . . . . . . 30 11.2. Informative References . . . . . . . . . . . . . . . . . . 34
10.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34
10.7. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 30
10.7.1. Arriving at source . . . . . . . . . . . . . . . . . . 30
10.7.2. Fatal error . . . . . . . . . . . . . . . . . . . . . 30
10.7.3. No previous hop . . . . . . . . . . . . . . . . . . . 30
10.7.4. Traceroute shorter than requested . . . . . . . . . . 30
10.8. Continuing after an error . . . . . . . . . . . . . . . . 31
11. Protocol-Specific Considerations . . . . . . . . . . . . . . . 32
11.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 32
11.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 32
11.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 32
11.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 32
11.5. AMT . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
12. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 34
12.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 34
12.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 34
12.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 34
12.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 35
12.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 35
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
13.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 36
13.2. UDP Destination Port and IPv6 Address . . . . . . . . . . 36
14. Security Considerations . . . . . . . . . . . . . . . . . . . 37
14.1. Topology Discovery . . . . . . . . . . . . . . . . . . . . 37
14.2. Traffic Rates . . . . . . . . . . . . . . . . . . . . . . 37
14.3. Limiting Query/Request Rates . . . . . . . . . . . . . . . 37
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 38
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39
16.1. Normative References . . . . . . . . . . . . . . . . . . . 39
16.2. Informative References . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
1. Introduction 1. Introduction
Given a multicast distribution tree, tracing from a multicast source
to a receiver is difficult, since we do not know which branch of the
multicast tree the receiver lies. This means that we have to flood
the whole tree to find the path from a source to a receiver. On the
other hand, walking up the tree from a receiver to a source is easy,
as most existing multicast routing protocols know the upstream router
for each source. Tracing from a receiver to a source can involve
only the routers on the direct path.
This document specifies the multicast traceroute facility named This document specifies the multicast traceroute facility named
mtrace version 2 or mtrace2. Mtrace2 allows the tracing of an IP Mtrace version 2 or Mtrace2 which allows the tracing of an IP
multicast routing paths. Mtrace2 provides additional information multicast routing path. Mtrace2 is usually initiated from a Mtrace2
about packet rates and losses, or other diagnosis information. For client towards a specified source, or a Rendezvous Point (RP) if no
instance, mtrace2 is used for the following purposes. source address is specified. RP is a special router where the source
and receiver meet in PIM-SM [1]. Moreover, Mtrace2 provides
additional information such as the packet rates and losses, as well
as other diagnosis information. Especially, Mtrace2 can be used for
the following purposes:
o To trace the path that a packet would take from some source to o To trace the path that a packet would take from a source to a
some destination. receiver.
o To isolate packet loss problems (e.g., congestion). o To isolate packet loss problems (e.g., congestion).
o To isolate configuration problems (e.g., TTL threshold). o To isolate configuration problems (e.g., TTL threshold).
Mtrace2 consists of the client and router programs. The mtrace2 Figure 1 shows a typical case on how Mtrace2 is used. FHR represents
client program is invoked from somewhere in the multicast tree, on a the first-hop router, LHR represents the last-hop router, and the
host, router, or proxy such as IGMP/MLD proxy [8]. The node invoking arrow lines represent the Mtrace2 messages that are sent from one
the program is called the mtrace2 client. node to another. The numbers before the Mtrace2 messages represent
the sequence of the messages that would happen. Source, Receiver and
Mtrace2 client are typically a host on the Internet.
The mtrace2 client program creates the mtrace2 Query message, which 2. Request 2. Request
includes a source and multicast address specified by the client, and +----+ +----+
forwards the message to its neighbor router or proxy. This initiates | | | |
a trace of a multicast routing path from the client toward the v | v |
specified source, or if no source address is specified, toward a core +--------+ +-----+ +-----+ +----------+
router if such a router exists. In the case of PIM-SM [6], the core | Source |----| FHR |----- The Internet -----| LHR |----| Receiver |
router is an RP maintaining the specified multicast address. +--------+ +-----+ | +-----+ +----------+
\ | ^
\ | /
\ | /
\ | /
3. Reply \ | / 1. Query
\ | /
\ | /
\ +---------+ /
v | Mtrace2 |/
| client |
+---------+
When a router or proxy receives an mtrace2 Query message and has the Figure 1
corresponding routing state regarding the source and multicast
addresses specified in the Query, the router or proxy invokes the
mtrace2 router program. The mtrace2 router program creates an
mtrace2 Request message corresponding to the query and forwards the
Request toward the specified source or the core router.
When a first-hop router or proxy (a single hop from the source When an Mtrace2 client initiates a multicast trace anywhere on the
specified in the request) or the core router receives an mtrace2 Internet, it sends an Mtrace2 Query packet to the LHR for a multicast
Query or Request message, the router or proxy invokes the mtrace2 group and a source address. The LHR turns the Query packet into a
router program. The mtrace2 router program creates an mtrace2 Reply Request, appends a standard response block containing its interface
message. The Reply message is forwarded to the mtrace2 client, thus addresses and packet statistics to the Request packet, then forwards
completing the mtrace2 Request. the packet towards the source. The Request packet is either
unicasted to its upstream router towards the source, or multicasted
to the group if the upsteam router's IP address is not known. In a
similar fashion, each router along the path to the source appends a
standard response block to the end of the Request packet before
forwarding it to its upstream router. When the FHR receives the
Request packet, it appends its own standard response block, turns the
Request packet into a Reply, and unicasts the Reply back to the
Mtrace2 client.
The mtrace2 client program waits for the mtrace2 Reply message and The Mtrace2 Reply may be returned before reaching the FHR if it
displays the results. When an mtrace2 Reply message does not come reaches the RP first, or a fatal error condition such as "no route"
due to network congestion, a broken router (see Section 10.6) or a is encountered along the path, or the hop count is exceeded.
non-responding router (see Section 10.8), the mtrace2 client program
can resend an mtrace2 Query with a lower hop count (see Section 5.1)
and repeat the process until it receives an mtrace2 Reply message.
The mtrace2 client should also be aware that the mtrace2 Query may The Mtrace2 client waits for the Mtrace2 Reply message and displays
follow the control path on the routers, in the case of a router's the results. When not receiving an Mtrace2 Reply message due to
control plane and forwarding plane are not synchronized, e.g., a network congestion, a broken router (see Section 5.6), or a non-
buggy implementation. In this case, mtrace2 Requests will be responding router (see Section 5.7), the Mtrace2 client may resend
forwarded toward the specified source or the core router because the another Mtrace2 Query with a lower hop count (see Section 3.2.1), and
router does not have any forwarding state for the query. repeat the process until it receives an Mtrace2 Reply message. The
details are Mtrace2 client specific, and it is outside the scope of
this document.
The mtrace2 supports both IPv4 and IPv6 multicast traceroute Note that when a router's control plane and forwarding plane are out
facility. The protocol design, concept, and program behavior are of sync, the Mtrace2 Requests might be forwarded based on the control
same between IPv4 and IPv6 mtrace2. While the original IPv4 states instead. In which case, the traced path might not represent
multicast traceroute, mtrace, the query and response messages are the real path the data packets would follow.
implemented as IGMP messages [10], all mtrace2 messages are carried
on UDP. The packet formats of IPv4 and IPv6 mtrace2 are different Mtrace2 supports both IPv4 and IPv6. Unlike the previous version of
because of the different address families, but the syntax is similar. Mtrace, which implements its query and response as IGMP messages [8],
all Mtrace2 messages are UDP-based. Although the packet formats of
IPv4 and IPv6 Mtrace2 are different because of the address families,
the syntax between them is similar.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL In this document, the key words "MUST", "MUST NOT", "REQUIRED",
NOT","SHOULD", "SHOULD NOT", "RECOMMENDED","MAY", and "OPTIONAL" in "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
this document are to be interpreted as described in RFC 2119 [1]. and "OPTIONAL" are to be interpreted as described in RFC 2119 [2],
and indicate requirement levels for compliant Mtrace2
implementations.
Since multicast traceroutes flow in the opposite direction to the 2.1. Definitions
data flow, we refer to "upstream" and "downstream" with respect to
data, unless explicitly specified.
Incoming interface: Since Mtrace2 Queries and Requests flow in the opposite direction to
The interface on which traffic is expected from the specified source the data flow, we refer to "upstream" and "downstream" with respect
and group. to data, unless explicitly specified.
Outgoing interface: Incoming interface
The interface on which traffic is forwarded from the specified source The interface on which data is expected to arrive from the
and group toward the destination. It is the interface on which the specified source and group.
mtrace2 Query or Request was received.
Previous-hop router: Outgoing interface
The router that is on the link attached to the Incoming interface and The interface to which data from the source or RP is expected to
is responsible for forwarding traffic for the specified source and transmit for the specified source and group. It is also the
group. interface on which the Mtrace2 Request will be received.
Last-hop router: Upstream router
The router that is on the link attached to the Outgoing interface and The router, connecting to the Incoming interface of the current
receives the mtrace2 Query from the adjacent mtrace2 client. router, which is responsible for forwarding data for the specified
source and group to the current router.
Group state: First-hop router (FHR)
It is the state in which a shared-tree protocol (e.g., PIM-SM [6]) The router that is directly connected to the source the Mtrace2
running on a router chooses the previous-hop router toward the core Query specifies.
router or Rendezvous Point (RP) as its parent router. In this state,
source-specific state is not available for the corresponding
multicast address on the router.
Source-specific state: Last-hop router (LHR)
It is the state in which a routing protocol running on a router The router that is directly connected to the receivers. It is
chooses the path that would be followed for a source-specific join. also the router that receives the Mtrace2 Query from an Mtrace2
client.
ALL-[protocol]-ROUTERS.MCAST.NET: Group state
It is a dedicated multicast address for a multicast router to It is the state a shared-tree protocol, such as PIM-SM [1], uses
communicate with other routers that are working with the same routing to choose the upstream router towards the RP for the specified
protocol. For instance, the address of ALL-PIM-ROUTERS.MCAST.NET [6] group. In this state, source-specific state is not available for
is '224.0.0.13' for IPv4 and 'ff02::d' for IPv6. the corresponding group address on the router.
3. Overview Source-specific state
It is the state that is used to choose the path towards the source
for the specified source and group.
Given a multicast distribution tree, tracing from a source to a ALL-[protocol]-ROUTERS.MCAST.NET
multicast destination is hard, since you do not know down which It is a link-local multicast address for multicast routers to
branch of the multicast tree the destination lies. This means that communicate with their adjacent routers that are running the same
you have to flood the whole tree to find the path from one source to routing protocol. For instance, the address of ALL-PIM-
one destination. However, walking up the tree from destination to ROUTERS.MCAST.NET [1] is '224.0.0.13' for IPv4 and 'ff02::d' for
source is easy, as most existing multicast routing protocols know the IPv6.
previous hop for each source. Tracing from destination to source can
involve only routers on the direct path.
The party requesting the multicast traceroute sends a traceroute 3. Packet Formats
Query packet to the last-hop multicast router for the given multicast
address. The last-hop router turns the Query into a Request packet
by changing the packet type and adding a response data block
containing its interface addresses and packet statistics, and then
forwards the Request packet via unicast to the router that the last-
hop router believes is the proper previous hop for the given source
and group. Each hop adds its response data to the end of the Request
packet, then unicast forwards it to the previous hop. The first-hop
router (the router that believes that packets from the source
originate on one of its directly connected networks) changes the
packet type to indicate a Reply packet and sends the completed Reply
to the mtrace2 client address specified in the Query header. The
Reply may be returned before reaching the first-hop router if a fatal
error condition such as "no route" is encountered along the path or
hop count is exceeded.
Multicast traceroute uses any information available to it in the This section describes the details of the packet formats for Mtrace2
router to attempt to determine a previous hop to forward the trace messages.
towards. Multicast routing protocols vary in the type and amount of
state they keep; multicast traceroute endeavors to work with all of
them by using whatever is available. For example, if a PIM-SM router
is on the (*,G) tree, it chooses the parent towards the RP as the
previous hop. In these cases, no source/group-specific state is
available, but the path may still be traced.
4. Packet Formats All Mtrace2 messages are encoded in TLV format (see Section 3.1). If
an implementation receives an unknown TLV, it SHOULD ignored and
silently discarded the unknown TLV. If the length of a TLV exceeds
the length specified in the TLV, the TLV SHOULD be accepted; however,
any additional data after the TLV SHOULD be ignored.
The mtrace2 message is carried as a UDP packet. The destination All Mtrace2 messages are UDP packets. For IPv4, Mtrace2 Query and
address of mtrace2 Query messages is either the last-hop router Request messages MUST NOT be fragmented. For IPv6, the packet size
unicast address or multicast address if the mtrace2 client does not for the Mtrace2 messages MUST NOT exceed 1280 bytes, which is the
know the proper last-hop router address. The destination address of smallest MTU for an IPv6 interface [3]. The source port is uniquely
mtrace2 Report messages is the address specified in Previous-Hop selected by the local host operating system. The destination port is
Router Address field in the last appended mtrace2 Standard Response the IANA reserved Mtrace2 port number (see Section 8). All Mtrace2
Block, which is either the previous-hop router unicast address or messages MUST have a valid UDP checksum.
multicast address. Detailed in Section 9.3.
Mtrace2 message is encoded in TLV format. If an implementation Additionally, Mtrace2 supports both IPv4 and IPv6, but not mixed.
receives a TLV whose length exceeds the TLV length specified in the For example, if an Mtrace2 Query or Reply message arrives in as an
Length field, the TLV SHOULD be accepted but any additional data IPv4 packet, all addresses specified in the Mtrace2 messages MUST be
SHOULD be ignored. If an implementation receives a TLV whose type IPv4 as well. Same rule applies to IPv6 Mtrace2 messages.
value is unknown, the mtrace2 message SHOULD be ignored and silently
dropped.
4.1. Mtrace2 TLV format 3.1. Mtrace2 TLV format
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value .... | | Type | Length | Value .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type (8 bits) Type: 8 bits
Length (16 bits) Describes the format of the Value field. For all the available
types, please see Section 3.2
Value (variable length) Length: 16 bits
4.2. Defined TLVs Length of Type, Length, and Value fields in octets. Minimum
length required is 6 octets. The maximum TLV length is not
defined; however the entired Mtrace2 packet length should not
exceeed the available MTU.
The following TLV Types are defined: Value: variable length
Code Type The format is based on the Type value. The length of the value
====== ====================================== field is Length field minus 3. All reserved fields in the Value
1 Mtrace2 Query field MUST be transmitted as zeros and ignored on receipt.
2 Mtrace2 Request
3 Mtrace2 Reply
4 Mtrace2 Standard Response Block
5 Mtrace2 Augmented Response Block
An mtrace2 message MUST contain exactly one Mtrace2 Query header. A 3.2. Defined TLVs
multicast router that sends an mtrace2 Request or Reply message MUST
add one mtrace2 Standard Response block to given mtrace2 message but
MUST NOT add multiple mtrace2 Standard Response blocks to it. A
multicast router that adds one mtrace2 Standard Response block to
given mtrace2 message MAY append one or multiple Augmented Response
blocks.
The TLV type field is defined to be "0x1" and "0x2" for mtrace2 The following TLV Types are defined:
Queries and Requests, respectively. An mtrace2 message containing
the type "0x1" is an mtrace2 Query. It is sent by an mtrace2 querier
(i.e., an mtrace2 client). It is changed to "0x2" by the proper
last-hop router. The type field is changed to "0x3" when the packet
is completed and sent as an mtrace2 Reply from the first-hop router
to the querier.
5. Mtrace2 Query Header Code Type
==== ================================
0x01 Mtrace2 Query
0x02 Mtrace2 Request
0x03 Mtrace2 Reply
0x04 Mtrace2 Standard Response Block
0x05 Mtrace2 Augmented Response Block
0x06 Mtrace2 Extended Query Block
The mtrace2 supports both IPv4 and IPv6. If the mtrace2 Query or Each Mtrace2 message MUST begin with either a Query, Request or Reply
Reply arrives in an IPv4 packet, all addresses specified in the TLV. The first TLV determines the type of each Mtrace2 message.
mtrace2 messages must be with IPv4 addresses. Following this TLV, there can be a sequence of optional Extended
Query Blocks. In the case of the Request and Reply message, it is
then followed by a sequence of Standard Response Blocks, each from a
multicast router on the path towards the source or the RP. In the
case more information is needed, a Standard Response Block can be
followed by one or multiple Augmented Response Blocks.
The mtrace2 message is carried as a UDP packet. The UDP source port We will describe each message type in details in the next few
is uniquely selected by the local host operating system. The UDP sections.
destination port is the IANA reserved mtrace2 port number (see
Section 13). The UDP checksum MUST be valid in mtrace2 messages.
The mtrace2 message includes the common mtrace2 Query header as 3.2.1. Mtrace2 Query
follows. The header is only filled in by the originator of the
mtrace2 Query; intermediate routers MUST NOT modify any of the
fields.
0 1 2 3 An Mtrace2 query is usually originated by an Mtrace2 client which
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 sends an Mtrace2 Query message to the LHR. When tracing towards the
+-+-+-+-+-+-+-+-+ source or the RP, the intermediate routers MUST NOT modify the Query
| # hops | message except the Type field.
An Mtrace2 Query message is shown as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | # Hops |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Multicast Address | | Multicast Address |
| | | |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| | | |
| Source Address | | Source Address |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Mtrace2 Client Address | | Mtrace2 Client Address |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query ID | Client Port # | | Query ID | Client Port # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 Figure 2
5.1. # hops: 8 bits # Hops: 8 bits
This field specifies the maximum number of hops that the Mtrace2
client wants to trace. If there are some error conditions in the
middle of the path that prevent an Mtrace2 Reply from being
received by the client, the client MAY issues another Mtrace2
Query with the lower number of hops until it receives a Reply from
the FHR.
This field specifies the maximum number of hops that the mtrace2 Multicast Address: 32 bits or 128 bits
client wants to trace. If there is some error condition in the This field specifies an IPv4 or IPv6 address, which can be either:
middle of the path that prevents an mtrace2 Reply from being received
by the client, the client issues another mtrace2 Query with the lower
number of hops until it receives a Reply from the first-hop router.
5.2. Multicast Address m-1: a multicast group address to be traced; or,
This field specifies the 32 bits length IPv4 or 128 bits length IPv6 m-2: all 1's in case of IPv4 or the unspecified address (::) in
multicast address to be traced, or is filled with "all 1" in case of case of IPv6 if no group-specific information is desired.
IPv4 or with the unspecified address (::) in case of IPv6 if no
group-specific information is desired. Note that non-group-specific
mtrace2 MUST specify source address.
5.3. Source Address Source Address: 32 bits or 128 bits
This field specifies an IPv4 or IPv6 address, which can be either:
This field specifies the 32 bits length IPv4 or 128 bits length IPv6 s-1: an unicast address of the source to be traced; or,
address of the multicast source for the path being traced, or is
filled with "all 1" in case of IPv4 or with the unspecified address
(::) in case of IPv6 if no source-specific information such as a
trace for RPT in PIM-SM is desired. Note that non-source-specific
traceroutes may not be possible with certain multicast routing
protocols.
5.4. Mtrace2 Client Address s-2: all 1's in case of IPv4 or the unspecified address (::) in
case of IPv6 if no source-specific information is desired.
For example, the client is tracing a (*,g) group state.
This field specifies the 32 bits length IPv4 or 128 bits length IPv6 Note that it is invalid to have a source-group combination of
global address of the mtrace2 client. The trace starts at this (s-2, m-2). If a router receives such combination in an Mtrace2
client address and proceeds toward the traffic source. Query, it MUST silently discard the Query.
5.5. Query ID: 16 bits Mtrace2 Client Address: 32 bits or 128 bits
This field specifies the Mtrace2 client's IPv4 address or IPv6
global address. This address MUST be a valid unicast address, and
therefore, MUST NOT be all 1's or an unspecified address. The
Mtrace2 Reply will be sent to this address.
This field is used as a unique identifier for this mtrace2 Request so Query ID: 16 bits
that duplicate or delayed Replies may be detected. This field is used as a unique identifier for this Mtrace2 Query
so that duplicate or delayed Reply messages may be detected.
5.6. Client Port # Client Port #: 16 bits
This field specifies the destination UDP port number for receiving
the Mtrace2 Reply packet.
Mtrace2 Reply is sent back to the address specified in an Mtrace2 3.2.2. Mtrace2 Extended Query Block
Client Address field. This field specifies the UDP port number the
router will send Mtrace2 Reply. This client port number MUST NOT be
changed by any router.
6. IPv4 Mtrace2 Standard Response Block There may be a sequence of optional Extended Query Blocks that follow
an Mtrace2 Query to further specify any information needed for the
Query. For example, an Mtrace2 client might be interested in tracing
the path the specified source and group would take based on a certain
topology. In which case, the client can pass in the multi-topology
ID as the Value for an Extended Query Type (see below). The Extended
Query Type is extensible and the behavior of the new types will be
addressed by seperate documents.
Each intermediate IPv4 router in a trace path appends "response data The Mtrace2 Extended Query Block is formatted as follows:
block" to the forwarded trace packet. The standard response data
block looks as follows.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ | | Type | Length | MBZ |T|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Query Type | Value .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
MBZ: 7 bits
This field must be zeroed on transmission and ignored on
reception.
T-bit (Transitive Attribute): 1 bit
If the TLV type is unrecognized by the receiving router, then this
TLV is either discarded or forwarded along with the Query,
depending on the value of this bit. If this bit is set, then the
router MUST forward this TLV. If this bit is clear, the router
MUST send an mtrace2 Reply with an UNKNOWN_QUERY error.
Extended Query Type: 16 bits
This field specifies the type of the Extended Query Block.
Value: 16 bits
This field specifies the value of this Extended Query.
3.2.3. Mtrace2 Request
The format of an Mtrace2 Request message is similar to an Mtrace2
Query except the Type field is 0x02.
When a LHR receives an Mtrace2 Query message, it would turn the Query
into a Request by changing the Type field of the Query from 0x01 to
0x02. The LHR would then append an Mtrace2 Standard Response Block
(see Section 3.2.5) of its own to the Request message before sending
it upstream. The upstream routers would do the same without changing
the Type field until one of them is ready to send a Reply.
3.2.4. Mtrace2 Reply
The format of an Mtrace2 Reply message is similar to an Mtrace2 Query
except the Type field is 0x03.
When a FHR or a RP receives an Mtrace2 Request message which is
destined to itself, it would append an Mtrace2 Standard Response
Block (see Section 3.2.5) of its own to the Request message. Next,
it would turn the Request message into a Reply by changing the Type
field of the Request from 0x02 to 0x03. The Reply message would then
be unicated to the Mtrace2 client specified in the Mtrace2 Client
Address field.
There are a number of cases an intermediate router might return a
Reply before a Request reaches the FHR or the RP. See Section 4.1.1,
Section 4.2.2, Section 4.3.3, and Section 4.5 for more details.
3.2.5. IPv4 Mtrace2 Standard Response Block
This section describes the message format of an IPv4 Mtrace2 Standard
Response Block. The Type field is 0x04.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query Arrival Time | | Query Arrival Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Incoming Interface Address | | Incoming Interface Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outgoing Interface Address | | Outgoing Interface Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Previous-Hop Router Address | | Upstream Router Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. Input packet count on incoming interface . . Input packet count on incoming interface .
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. Output packet count on outgoing interface . . Output packet count on outgoing interface .
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. Total number of packets for this source-group pair . . Total number of packets for this source-group pair .
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rtg Protocol | Multicast Rtg Protocol | | Rtg Protocol | Multicast Rtg Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fwd TTL | MBZ |S| Src Mask |Forwarding Code| | Fwd TTL | MBZ |S| Src Mask |Forwarding Code|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.1. MBZ: 8 bit MBZ: 8 bits
This field must be zeroed on transmission and ignored on
Must be zeroed on transmission and ignored on reception. reception.
6.2. Query Arrival Time: 32 bits
The Query Arrival Time is a 32-bit NTP timestamp specifying the
arrival time of the mtrace2 Request packet at this router. The 32-
bit form of an NTP timestamp consists of the middle 32 bits of the
full 64-bit form; that is, the low 16 bits of the integer part and
the high 16 bits of the fractional part.
The following formula converts from a UNIX timeval to a 32-bit NTP
timestamp:
query_arrival_time
= (tv.tv_sec + 32384) << 16 + ((tv.tv_usec << 10) / 15625)
The constant 32384 is the number of seconds from Jan 1, 1900 to Jan
1, 1970 truncated to 16 bits. ((tv.tv_usec << 10) / 15625) is a
reduction of ((tv.tv_usec / 100000000) << 16).
However, mtrace2 does not require synchronizing NTP timestamp among
all routers along paths to measure one-way latency. The use of Query
Arrival Time is useful to measure the packets per second (PPS).
Suppose that a client issues two queries Q1 and Q2, and the
corresponding requests R1 and R2 arrive at router X at t1 and t2,
then the client would be able to calculate the PPS at router X by
using the packet count results at t1 and t2.
6.3. Incoming Interface Address: 32 bits
This field specifies the address of the interface on which packets
from this source and group are expected to arrive, or 0 if unknown or
unnumbered.
6.4. Outgoing Interface Address: 32 bits
This field specifies the address of the interface on which packets
from this source and group flow to the specified destination, or 0 if
unknown or unnumbered.
6.5. Previous-Hop Router Address: 32 bits
This field specifies the router from which this router expects
packets from this source. This may be a multicast group (e.g. ALL-
[protocol]-ROUTERS.MCAST.NET) if the previous hop is not known
because of the workings of the multicast routing protocol. However,
it should be 0 if the incoming interface address is unknown or
unnumbered.
6.6. Input packet count on incoming interface: 64 bits
This field contains the number of multicast packets received for all
groups and sources on the incoming interface, or "all 1" if no count
can be reported. This counter may have the same value as
ifHCInMulticastPkts from the IF-MIB [12] for this interface.
6.7. Output packet count on outgoing interface: 64 bits
This field contains the number of multicast packets that have been
transmitted or queued for transmission for all groups and sources on
the outgoing interface, or "all 1" if no count can be reported. This
counter may have the same value as ifHCOutMulticastPkts from the IF-
MIB for this interface.
6.8. Total number of packets for this source-group pair: 64 bits
This field counts the number of packets from the specified source
forwarded by this router to the specified group, or "all 1" if no
count can be reported. If the S bit is set, the count is for the
source network, as specified by the Src Mask field. If the S bit is
set and the Src Mask field is 63, indicating no source-specific
state, the count is for all sources sending to this group. This
counter should have the same value as ipMcastRoutePkts from the
IPMROUTE-STD-MIB [13] for this forwarding entry.
6.9. Rtg Protocol: 16 bits
This field describes the routing protocol used to decide an RPF
interface for the requested source. This value should have the same
value as ipMcastRouteRtProtocol from the IPMROUTE-STD-MIB [13] for
this entry. If the router is not able to obtain this value, "all 0"
must be specified.
6.10. Multicast Rtg Protocol: 16 bits
This field describes the multicast routing protocol in use between
this router and the previous-hop router. This value should have the
same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [13] for
this entry. If the router does not able to obtain this value, "all
0" must be specified.
6.11. Fwd TTL: 8 bits
This field contains the TTL that a packet is required to have before
it will be forwarded over the outgoing interface.
6.12. S: 1 bit
This S bit indicates that the packet count for the source-group pair
is for the source network, as determined by masking the source
address with the Src Mask field.
6.13. Src Mask: 7 bits
This field contains the number of 1's in the netmask this router has
for the source (i.e. a value of 24 means the netmask is 0xffffff00).
If the router is forwarding solely on group state, this field is set
to 127 (0x7f).
6.14. Forwarding Code: 8 bits
This field contains a forwarding information/error code. Section 9.2
explains how and when the forwarding code is filled. Defined values
are as follows;
Value Name Description Query Arrival Time: 32 bits
The Query Arrival Time is a 32-bit NTP timestamp specifying the
arrival time of the Mtrace2 Query or Request packet at this
router. The 32-bit form of an NTP timestamp consists of the
middle 32 bits of the full 64-bit form; that is, the low 16 bits
of the integer part and the high 16 bits of the fractional part.
----- -------------- ------------------------------------------- The following formula converts from a UNIX timeval to a 32-bit NTP
timestamp:
0x00 NO_ERROR No error query_arrival_time
= (tv.tv_sec + 32384) << 16 + ((tv.tv_usec << 10) / 15625)
0x01 WRONG_IF Mtrace2 Request arrived on an interface The constant 32384 is the number of seconds from Jan 1, 1900 to
to which this router would not forward for Jan 1, 1970 truncated to 16 bits. ((tv.tv_usec << 10) / 15625) is
this source, group, destination. a reduction of ((tv.tv_usec / 100000000) << 16).
0x02 PRUNE_SENT This router has sent a prune upstream which Note that Mtrace2 does not require all the routers on the path to
applies to the source and group in the have synchronized clocks in order to measure one-way latency.
mtrace2 Request.
0x03 PRUNE_RCVD This router has stopped forwarding for this Additionally, Query Arrival Time is useful for measuring the
source and group in response to a request packet rate. For example, suppose that a client issues two
from the next hop router. queries, and the corresponding requests R1 and R2 arrive at router
X at time T1 and T2, then the client would be able to compute the
packet rate on router X by using the packet count information
stored in the R1 and R2, and the time T1 and T2.
0x04 SCOPED The group is subject to administrative Incoming Interface Address: 32 bits
scoping at this hop. This field specifies the address of the interface on which packets
from the source or the RP are expected to arrive, or 0 if unknown
or unnumbered.
0x05 NO_ROUTE This router has no route for the source or Outgoing Interface Address: 32 bits
group and no way to determine a potential This field specifies the address of the interface on which packets
route. from the source or the RP are expected to transmit towards the
receiver, or 0 if unknown or unnumbered. This is also the address
of the interface on which the Mtrace2 Query or Request arrives.
0x06 WRONG_LAST_HOP This router is not the proper last-hop Upstream Router Address: 32 bits
router. This field specifies the address of the upstream router from which
this router expects packets from this source. This may be a
multicast group (e.g. ALL-[protocol]-ROUTERS.MCAST.NET) if the
upstream router is not known because of the workings of the
multicast routing protocol. However, it should be 0 if the
incoming interface address is unknown or unnumbered.
0x07 NOT_FORWARDING This router is not forwarding this source, Input packet count on incoming interface: 64 bits
group out the outgoing interface for an This field contains the number of multicast packets received for
unspecified reason. all groups and sources on the incoming interface, or all 1's if no
count can be reported. This counter may have the same value as
ifHCInMulticastPkts from the IF-MIB [9] for this interface.
0x08 REACHED_RP Reached Rendezvous Point or Core Output packet count on outgoing interface: 64 bit
This field contains the number of multicast packets that have been
transmitted or queued for transmission for all groups and sources
on the outgoing interface, or all 1's if no count can be reported.
This counter may have the same value as ifHCOutMulticastPkts from
the IF-MIB [9] for this interface.
0x09 RPF_IF Mtrace2 Request arrived on the expected Total number of packets for this source-group pair: 64 bits
RPF interface for this source and group. This field counts the number of packets from the specified source
forwarded by the router to the specified group, or all 1's if no
count can be reported. If the S bit is set (see below), the count
is for the source network, as specified by the Src Mask field (see
below). If the S bit is set and the Src Mask field is 63,
indicating no source-specific state, the count is for all sources
sending to this group. This counter should have the same value as
ipMcastRoutePkts from the IPMROUTE-STD-MIB [10] for this
forwarding entry.
0x0A NO_MULTICAST Mtrace2 Request arrived on an interface Rtg Protocol: 16 bits
which is not enabled for multicast. This field describes the unicast routing protocol running between
this router and the upstream router, and it is used to determine
the RPF interface for the specified source or RP. This value
should have the same value as ipMcastRouteRtProtocol from the
IPMROUTE-STD-MIB [10] for this entry. If the router is not able
to obtain this value, all 0's must be specified.
0x0B INFO_HIDDEN One or more hops have been hidden from this Multicast Rtg Protocol: 16 bits
trace. This field describes the multicast routing protocol in use between
the router and the upstream router. This value should have the
same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [10]
for this entry. If the router cannot obtain this value, all 0's
must be specified.
0x0C REACHED_GW Mtrace2 Request arrived on a gateway (e.g., Fwd TTL: 8 bits
a NAT or firewall) that hides the This field contains the TTL in which an Mtrace2 Request packet can
information between this router and the be forwarded towards the source or the RP.
mtrace2 querier
0x81 NO_SPACE There was not enough room to insert another S: 1 bit
response data block in the packet. If this bit is set, it indicates that the packet count for the
source-group pair is for the source network, as determined by
masking the source address with the Src Mask field.
0x82 ADMIN_PROHIB Mtrace2 is administratively prohibited. Src Mask: 7 bits
This field contains the number of 1's in the netmask the router
has for the source (i.e. a value of 24 means the netmask is
0xffffff00). If the router is forwarding solely on group state,
this field is set to 127 (0x7f).
Note that if a router discovers there is not enough room in a packet Forwarding Code: 8 bits
to insert its response, it puts the NO_SPACE code value in the This field contains a forwarding information/error code.
previous router's Forwarding Code field, overwriting any error the Section 4.1 and Section 4.2 will explain how and when the
previous router placed there. After the router sends the Reply to Forwarding Code is filled. Defined values are as follows:
the Mtrace2 Client Address in the header, the router continues the
mtrace2 Query by sending an mtrace2 Request containing the same
mtrace2 Query header. Section 9.3 and Section 10.8 include the
details.
The 0x80 bit of the Forwarding Code is used to indicate a fatal Value Name Description
error. A fatal error is one where the router may know the previous ----- -------------- ----------------------------------------------
hop but cannot forward the message to it. 0x00 NO_ERROR No error
0x01 WRONG_IF Mtrace2 Request arrived on an interface
to which this router would not forward for
the specified group towards the source or RP.
0x02 PRUNE_SENT This router has sent a prune upstream which
applies to the source and group in the
Mtrace2 Request.
0x03 PRUNE_RCVD This router has stopped forwarding for this
source and group in response to a request
from the downstream router.
0x04 SCOPED The group is subject to administrative
scoping at this router.
0x05 NO_ROUTE This router has no route for the source or
group and no way to determine a potential
route.
0x06 WRONG_LAST_HOP This router is not the proper LHR.
0x07 NOT_FORWARDING This router is not forwarding this source and
group out the outgoing interface for an
unspecified reason.
0x08 REACHED_RP Reached the Rendezvous Point.
0x09 RPF_IF Mtrace2 Request arrived on the expected
RPF interface for this source and group.
0x0A NO_MULTICAST Mtrace2 Request arrived on an interface
which is not enabled for multicast.
0x0B INFO_HIDDEN One or more hops have been hidden from this
trace.
0x0C REACHED_GW Mtrace2 Request arrived on a gateway (e.g.,
a NAT or firewall) that hides the
information between this router and the
Mtrace2 client.
0x0D UNKNOWN_QUERY A non-transitive Extended Query Type was
received by a router which does not support
the type.
0x80 FATAL_ERROR A fatal error is one where the router may
know the upstream router but cannot forward
the message to it.
0x81 NO_SPACE There was not enough room to insert another
Standard Response Block in the packet.
0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited.
7. IPv6 Mtrace2 Standard Response Block 3.2.6. IPv6 Mtrace2 Standard Response Block
Each intermediate IPv6 router in a trace path appends "response data This section describes the message format of an IPv6 Mtrace2 Standard
block" to the forwarded trace packet. The standard response data Response Block. The Type field is also 0x04.
block looks as follows.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ | | Type | Length | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query Arrival Time | | Query Arrival Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Incoming Interface ID | | Incoming Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outgoing Interface ID | | Outgoing Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
* Local Address * * Local Address *
| | | |
skipping to change at page 19, line 44 skipping to change at page 17, line 38
| | | |
. Output packet count on outgoing interface . . Output packet count on outgoing interface .
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. Total number of packets for this source-group pair . . Total number of packets for this source-group pair .
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rtg Protocol | Multicast Rtg Protocol | | Rtg Protocol | Multicast Rtg Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ |S|Src Prefix Len |Forwarding Code| | MBZ 2 |S|Src Prefix Len |Forwarding Code|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7.1. MBZ: 8 bit MBZ: 8 bits
This field must be zeroed on transmission and ignored on
Must be zeroed on transmission and ignored on reception. reception.
7.2. Query Arrival Time: 32 bits
Same definition described in Section 6.2
7.3. Incoming Interface ID: 32 bits
This field specifies the interface ID on which packets from this
source and group are expected to arrive, or 0 if unknown. This ID
should be the value taken from InterfaceIndex of the IF-MIB [12] for
this interface. This field is carried in network byte order.
7.4. Outgoing Interface ID: 32 bits
This field specifies the interface ID on which packets from this
source and group flow to the specified destination, or 0 if unknown.
This ID should be the value taken from InterfaceIndex of the IF-MIB
for this interface. This field is carried in network byte order.
7.5. Local Address Query Arrival Time: 32 bits
Same definition as in IPv4.
This field specifies a global IPv6 address that uniquely identifies Incoming Interface ID: 32 bits
the router. A unique local unicast address [11] SHOULD NOT be used This field specifies the interface ID on which packets from the
unless the router is only assigned link-local and unique local source or RP are expected to arrive, or 0 if unknown. This ID
addresses. If the router is only assigned link-local addresses, its should be the value taken from InterfaceIndex of the IF-MIB [9]
link-local address can be specified in this field. for this interface.
7.6. Remote Address Outgoing Interface ID: 32 bits
This field specifies the interface ID to which packets from the
source or RP are expected to transmit, or 0 if unknown. This ID
should be the value taken from InterfaceIndex of the IF-MIB [9]
for this interface
This field specifies the address of the previous-hop router, which, Local Address: 128 bits
in most cases, is a link-local unicast address for the queried source This field specifies a global IPv6 address that uniquely
and destination addresses. identifies the router. An unique local unicast address [11]
SHOULD NOT be used unless the router is only assigned link-local
and unique local addresses. If the router is only assigned link-
local addresses, its link-local address can be specified in this
field.
Although a link-local address does not have enough information to Remote Address: 128 bits
identify a node, it is possible to detect the previous-hop router This field specifies the address of the upstream router, which, in
with the assistance of Incoming Interface ID and the current router most cases, is a link-local unicast address for the upstream
address (i.e., Local Address). router.
This may be a multicast group (e.g., ALL-[protocol]- Although a link-local address does not have enough information to
ROUTERS.MCAST.NET) if the previous hop is not known because of the identify a node, it is possible to detect the upstream router with
workings of the multicast routing protocol. However, it should be the assistance of Incoming Interface ID and the current router
the unspecified address (::) if the incoming interface address is address (i.e., Local Address).
unknown.
7.7. Input packet count on incoming interface Note that this may be a multicast group (e.g., ALL-[protocol]-
ROUTERS.MCAST.NET) if the upstream router is not known because of
the workings of a multicast routing protocol. However, it should
be the unspecified address (::) if the incoming interface address
is unknown.
Same definition described in Section 6.6 Input packet count on incoming interface: 64 bits
Same definition as in IPv4.
7.8. Output packet count on outgoing interface Output packet count on outgoing interface: 64 bits
Same definition as in IPv4.
Same definition described in Section 6.7 Total number of packets for this source-group pair: 64 bits
Same definition as in IPv4, except if the S bit is set (see
below), the count is for the source network, as specified by the
Src Prefix Len field. If the S bit is set and the Src Prefix Len
field is 255, indicating no source-specific state, the count is
for all sources sending to this group. This counter should have
the same value as ipMcastRoutePkts from the IPMROUTE-STD-MIB [10]
for this forwarding entry.
7.9. Total number of packets for this source-group pair Rtg Protocol: 16 bits
Same definition as in IPv4.
This field counts the number of packets from the specified source Multicast Rtg Protocol: 16 bits
forwarded by this router to the specified group, or "all 1" if no Same definition as in IPv4.
count can be reported. If the S bit is set, the count is for the
source network, as specified by the Src Prefix Len field. If the S
bit is set and the Src Prefix Len field is 255, indicating no source-
specific state, the count is for all sources sending to this group.
This counter should have the same value as ipMcastRoutePkts from the
IPMROUTE-STD-MIB for this forwarding entry.
7.10. Rtg Protocol: 16 bits MBZ 2: 15 bits
This field must be zeroed on transmission and ignored on
reception.
Same definition described in Section 6.9 S: 1 bit
Same definition as in IPv4, except the Src Prefix Len field is
used to mask the source address.
7.11. Multicast Rtg Protocol: 16 bits Src Prefix Len: 8 bits
This field contains the prefix length this router has for the
source. If the router is forwarding solely on group state, this
field is set to 255 (0xff).
Same definition described in Section 6.10 Forwarding Code: 8 bits
Same definition as in IPv4.
7.12. S: 1 bit 3.2.7. Mtrace2 Augmented Response Block
This S bit indicates that the packet count for the source-group pair In addition to the Standard Response Block, a multicast router on the
is for the source network, as determined by masking the source traced path can optionally add one or multiple Augmented Response
address with the Src Prefix Len field. Blocks before sending the Request to its upstream router.
7.13. Src Prefix Len: 8 bits The Augmented Response Block is flexible for various purposes such as
providing diagnosis information (see Section 7) and protocol
verification. It's Type field is 0x05, and its format is as follows:
This field contains the prefix length this router has for the source. 0 1 2 3
If the router is forwarding solely on group state, this field is set 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
to 255 (0xff) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Augmented Response Type | Value .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7.14. Forwarding Code: 8 bits MBZ: 8 bits
This field must be zeroed on transmission and ignored on
reception.
Same definition described in Section 6.14 Augmented Response Type: 16 bits
This field specifies the type of various responses from a
multicast router that might need to communicate back to the
Mtrace2 client as well as the multicast routers on the traced
path.
8. Mtrace2 Augmented Response Block The Augmented Response Type is defined as follows:
In addition to the standard response block, a multicast router on the Code Type
path will be able to add "augumented response block" when it sends ==== ===============================================
the mtrace2 Request to its upstream router or sends the Reply to the 0x01 # of the returned Standard Response Blocks
Mtrace2 Client Address. This augmented response block is flexible to
add various information.
0 1 2 3 When the NO_SPACE error occurs on a router, the router should send
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 the original Mtrace2 Request received from the downstream router
+-+-+-+-+-+-+-+-+ as a Reply back to the Mtrace2 client, and continue with a new
| MBZ | Mtrace2 Request. In the new Request, the router would add a
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Standard Response Block followed by an Augmented Response Block
| Type | Value .... | with 0x01 as the Augmented Response Type, and the number of the
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ returned Mtrace2 Standard Response Blocks as the Value.
The augmented response block is always appended to mtrace2 TLV header Each upstream router would recognize the total number of hops the
(0x04). The 16 bits Type filed of the augmented response block is Request has been traced so far by adding this number and the
defined for various purposes, such as diagnosis (as in Section 12) number of the Standard Response Block in the current Request
and protocol verification. The packet length of the augmented message.
response block is specified in the augmented response block TLV
header as seen in Section 4.1.
The following augmented response block type is defined: This document only defines one Augmented Response Type in the
Augmented Response Block. The description on how to provide
diagnosis information using the Augmented Response Block is out of
the scope of this document, and will be addressed in separate
documents.
Code Type Value: variable length
====== ================================================= The format is based on the Augmented Response Type value. The
0x01 # Mtrace2 Standard Response Blocks Returned length of the value field is Length field minus 6.
When the NO_SPACE error occurs, the router sends back the mtrace2 4. Router Behavior
Reply with contained data (i.e., all appended response blocks), and
continues the mtrace2 Query by sending an mtrace2 Request as will be
described in Section 9.3. In this mtrace2 Request, the router
appends the augmented response block with the code "0x01" and the
number of returned mtrace2 response blocks. Every router between
this router and the first-hop router can recognize the limit number
of hops by referring this number and the # hops in the header.
This document only defines the above augmented response block type This section describes the router behavior in the context of Mtrace2
and does not define other augmented response block types. Specifing in details.
how to deal with diagnosis information will be also described in
separate documents.
9. Router Behavior 4.1. Receiving Mtrace2 Query
All of these actions are performed in addition to (NOT instead of) An Mtrace2 Query message is an Mtrace2 message with no response
forwarding the packet, if applicable. E.g. a multicast packet that blocks filled in, and uses TLV type of 0x01.
has TTL or the hop limit remaining MUST be forwarded normally, as
MUST a unicast packet that has TTL or the hop limit remaining and is
not addressed to this router.
9.1. Receiving Mtrace2 Query 4.1.1. Query Packet Verification
An mtrace2 Query message is an mtrace2 message with no response Upon receiving an Mtrace2 Query message, a router MUST examine
blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 mtrace2. whether the Multicast Address and the Source Address are a valid
combination as specified in Section 3.2.1, and whether the Mtrace2
Client Address is a valid IP unicast address. If either one is
invalid, the Query MUST be silently ignored.
9.1.1. Packet Verification Mtrace2 supports non-local client to the LHR. It is up to the
implementation to filter out such queries.
Upon receiving an mtrace2 Query message, a router must examine the In the case when it is a local client, the router must then examine
Query to see if it is the proper last-hop router for the destination the Query to see if it is the proper LHR for the destination address
address in the packet. It is the proper last-hop router if it has a in the packet. It is the proper LHR if it has a multicast-capable
multicast-capable interface on the same subnet as the Mtrace2 Client interface on the same subnet as the Mtrace2 Client Address and is the
Address and is the router that would forward traffic from the given router that would forward traffic from the given (S,G) or (*,G) onto
(S,G) or (*,G) onto that subnet. that subnet.
If the router determines that it is not the proper last-hop router, If the router determines that it is not the proper LHR, or it cannot
or it cannot make that determination, it does one of two things make that determination, it does one of two things depending on
depending if the Query was received via multicast or unicast. If the whether the Query was received via multicast or unicast. If the
Query was received via multicast, then it MUST be silently dropped. Query was received via multicast, then it MUST be silently discarded.
If it was received via unicast, a forwarding code of WRONG_LAST_HOP If it was received via unicast, the router turns the Query into a
is noted and processing continues as in Section 9.2. Reply message by changing the TLV type to 0x03 and appending a
Standard Response Block with a Forwarding Code of WRONG_LAST_HOP.
The rest of the fields in the Standard Response Block MUST be zeroed.
The router then sends the Reply message to the Mtrace2 Client Address
on the Client Port # as specified in the Mtrace2 Query.
Duplicate Query messages as identified by the tuple (Mtrace2 Client Duplicate Query messages as identified by the tuple (Mtrace2 Client
Address, Query ID) SHOULD be ignored. This MAY be implemented using Address, Query ID) SHOULD be ignored. This MAY be implemented using
a simple 1-back cache (i.e. remembering the Mtrace2 Client Address a cache of previously processed queries keyed by the Mtrace2 Client
and Query ID of the previous Query message that was processed, and Address and Query ID pair. The duration of the cached entries is
ignoring future messages with the same Mtrace2 Client Address and implementation specific. Duplicate Request messages MUST NOT be
Query ID). Duplicate Request messages MUST NOT be ignored in this ignored in this manner.
manner.
9.1.2. Normal Processing 4.1.2. Query Normal Processing
When a router receives an mtrace2 Query and it determines that it is When a router receives an Mtrace2 Query and it determines that it is
the proper last-hop router, it it changes the TLV type to 0x2 and the proper LHR, it turns the Query to a Request by changing the TLV
treats it like an mtrace2 Request and performs the steps listed in type from 0x01 to 0x02, and performs the steps listed in Section 4.2.
Section 9.2.
9.1.3. Mtrace2 Query Received by Non-Supported Router 4.2. Receiving Mtrace2 Request
When a router that does not support mtrace2 receives an mtrace2 Query An Mtrace2 Request is an Mtrace2 message that uses TLV type of 0x02.
message whose destination address is multicast, the router will With the exception of the LHR, whose Request was just converted from
silently discard the message. When the router receives an mtrace2 a Query, each Request received by a router should have at least one
Query message whose destination address is the router's interface Standard Response Block filled in.
address, the router returns an ICMP Port unreachable to the Mtrace2
Client Address.
9.2. Receiving Mtrace2 Request 4.2.1. Request Packet Verification
An mtrace2 Request is a traceroute message with some number of If the Mtrace2 Request does not come from an adjacent router, or if
response blocks filled in, and uses TLV type 0x2 for IPv4 and IPv6 the Request is not addressed to this router, or if the Request is
mtrace2. addressed to a multicast group which is not a link-scoped group (i.e.
9.2.1. Packet Verification 224/24 for IPv4, FFx2::/16 [4] for IPv6), it MUST be silently
ignored. GTSM [12] SHOULD be used by the router to determine whether
the router is adjacent or not.
If the mtrace2 Request does not come from an adjacent host or router, If the sum of the number of the Standard Response Blocks in the
it MUST be silently ignored. If the mtrace2 Request is not addressed received Mtrace2 Request and the value of the Augmented Response Type
to this router, or if the Request is addressed to a multicast group of 0x01, if any, is equal or more than the # Hops in the Mtrace2
which is not a link-scoped group (i.e. 224/24 for IPv4, FFx2::/16 [3] Request, it MUST be silently ignored.
for IPv6), it MUST be silently ignored. GTSM [14] SHOULD be used by
the router to determine whether the host or router is adjacent or
not.
9.2.2. Normal Processing 4.2.2. Request Normal Processing
When a router receives an mtrace2 Request, it performs the following When a router receives an Mtrace2 Request message, it performs the
steps. Note that it is possible to have multiple situations covered following steps. Note that it is possible to have multiple
by the Forwarding Codes. The first one encountered is the one that situations covered by the Forwarding Codes. The first one
is reported, i.e. all "note forwarding code N" should be interpreted encountered is the one that is reported, i.e. all "note Forwarding
as "if forwarding code is not already set, set forwarding code to N". Code N" should be interpreted as "if Forwarding Code is not already
set, set Forwarding Code to N".
1. If there is room in the current buffer (or the router can 1. Prepare a Standard Response Block to be appended to the packet
efficiently allocate more space to use), insert a new response and fill in the Query Arrival Time, Outgoing Interface Address
block into the packet and fill in the Query Arrival Time, (for IPv4) or Outgoing Interface ID (for IPv6), Output Packet
Outgoing Interface Address (for IPv4 mtrace2) or Outgoing Count, and Fwd TTL (for IPv4). Note that the Outgoing Interface
Interface ID (for IPv6 mtrace2), Output Packet Count, and Fwd is the one on which the Mtrace2 Request message arrives.
TTL (for IPv4 mtrace2). If there was no room, fill in the
forwarding code "NO_SPACE" in the *previous* hop's response
block, and forward the packet to the address specified in the
Mtrace2 Client Address field and continue the trace as described
in Section 9.3.
2. Attempt to determine the forwarding information for the source 2. Attempt to determine the forwarding information for the
and group specified, using the same mechanisms as would be used specified source and group, using the same mechanisms as would
when a packet is received from the source destined for the be used when a packet is received from the source destined for
group. A state need not be instantiated, it can be "phantom" the group. A state need not be instantiated, it can be a
state created only for the purpose of the trace, such as "dry- "phantom" state created only for the purpose of the trace, such
run". as "dry-run."
If using a shared-tree protocol and there is no source-specific If using a shared-tree protocol and there is no source-specific
state, or if no source-specific information is desired (i.e., state, or if no source-specific information is desired (i.e.,
"all 1" for IPv4 or unspecified address (::) for IPv6), group all 1's for IPv4 or unspecified address (::) for IPv6), group
state should be used. If there is no group state or no group- state should be used. If there is no group state or no group-
specific information is desired, potential source state (i.e., specific information is desired, potential source state (i.e.,
the path that would be followed for a source-specific Join) the path that would be followed for a source-specific Join)
should be used. If this router is the Core or RP and no source- should be used.
specific state is available (e.g., this router has been
receiving PIM Register messages from the first-hop router), note
a code of REACHED_RP.
3. If no forwarding information can be determined, the router notes 3. If no forwarding information can be determined, the router notes
a forwarding code of NO_ROUTE, sets the remaining fields that a Forwarding Code of NO_ROUTE, sets the remaining fields that
have not yet been filled in to zero, and then forwards the have not yet been filled in to zero, and then sends an Mtrace2
packet to the mtrace2 client as described in Section 9.3. Reply back to the Mtrace2 client.
4. Fill in the Incoming Interface Address, Previous-Hop Router 4. Fill in the Incoming Interface Address, Upstream Router Address,
Address, Input Packet Count, Total Number of Packets, Routing Input Packet Count, Total Number of Packets, Routing Protocol,
Protocol, S, and Src Mask from the forwarding information that S, and Src Mask (or Src Prefix Len for IPv6) using the
was determined. forwarding information determined by the step 2.
5. If mtrace2 is administratively prohibited, note the appropriate 5. If Mtrace2 is administratively prohibited, note the Forwarding
forwarding code (ADMIN_PROHIB). If mtrace2 is administratively Code of ADMIN_PROHIB. If Mtrace2 is administratively prohibited
prohibited and any of the fields as filled in step 4 are and any of the fields as filled in the step 4 are considered
considered private information, zero out the applicable fields. private information, zero out the applicable fields.
Then the packet is forwarded to the mtrace2 client as described
in Section 9.3.
6. If the reception interface is not enabled for multicast, note 6. If the Outgoing interface is not enabled for multicast, note
forwarding code NO_MULTICAST. If the reception interface is the Forwarding Code of NO_MULTICAST. If the Outgoing interface is
interface from which the router would expect data to arrive from the interface from which the router would expect data to arrive
the source, note forwarding code RPF_IF. Otherwise, if the from the source, note forwarding code RPF_IF. If the Outgoing
reception interface is not one to which the router would forward interface is not one to which the router would forward data from
data from the source to the group, a forwarding code of WRONG_IF the source or RP to the group, a Forwarding code of WRONG_IF is
is noted. noted. In the above three cases, the router will return an
Mtrace2 Reply and terminate the trace.
7. If the group is subject to administrative scoping on either the 7. If the group is subject to administrative scoping on either the
Outgoing or Incoming interfaces, a forwarding code of SCOPED is Outgoing or Incoming interfaces, a Forwarding Code of SCOPED is
noted. noted.
8. If this router is the Rendezvous Point or Core for the group, a 8. If this router is the RP for the group, note a Forwarding Code
forwarding code of REACHED_RP is noted. of REACHED_RP. The router will send an Mtrace2 Reply and
terminate the trace.
9. If this router has sent a prune upstream which applies to the 9. If this router has sent a prune upstream which applies to the
source and group in the mtrace2 Request, it notes forwarding source and group in the Mtrace2 Request, it notes Forwarding
code PRUNE_SENT. If the router has stopped forwarding Code of PRUNE_SENT. If the router has stopped forwarding
downstream in response to a prune sent by the next hop router, downstream in response to a prune sent by the downstream router,
it notes forwarding code PRUNE_RCVD. If the router should it notes Forwarding Code of PRUNE_RCVD. If the router should
normally forward traffic for this source and group downstream normally forward traffic downstream for this source and group
but is not, it notes forwarding code NOT_FORWARDING. but is not, it notes Forwarding Code of NOT_FORWARDING.
10. If this router is a gateway (e.g., a NAT or firewall) that hides 10. If this router is a gateway (e.g., a NAT or firewall) that hides
the information between this router and the mtrace2 querier, it the information between this router and the Mtrace2 client, it
notes forwarding code REACHED_GW. notes Forwarding Code of REACHED_GW. The router continues the
processing as described in Section 4.5.
11. The packet is then sent on to the previous hop or the Mtrace2 11. If the total number of the Standard Response Blocks, including
Client Address as described in Section 9.3. the newly prepared one, and the value of the Augmented Response
Type of 0x01, if any, is less than the # Hops in the Request,
the packet is then forwarded to the upstream router as described
in Section 4.3; otherwise, the packet is sent as an Mtrace2
Reply to the Mtrace2 client as described in Section 4.4.
9.2.3. Mtrace2 Request Received by Non-Supported Router 4.3. Forwarding Mtrace2 Request
When a router that does not understand mtrace2 Request messages This section describes how an Mtrace2 Request should be forwarded.
receives an mtrace2 Request message whose destination address is
multicast, the router will silently discard the message. When the
router receives an mtrace2 Request message whose destination address
is the router's interface address, the router returns an ICMP Port
unreachable to the Mtrace2 Client Address, and the mtrace2 client may
then issue another mtrace2 Query with the lower number of # hops.
9.3. Forwarding Mtrace2 Request 4.3.1. Destination Address
9.3.1. Destination Address If the upstream router for the Mtrace2 Request is known for this
request, the Mtrace2 Request is sent to that router. If the Incoming
interface is known but the upstream router is not, the Mtrace2
Request is sent to an appropriate multicast address on the Incoming
interface. The multicast address SHOULD depend on the multicast
routing protocol in use, such as ALL-[protocol]-ROUTERS.MCAST.NET.
It MUST be a link-scoped group (i.e. 224/24 for IPv4, FF02::/16 for
IPv6), and MUST NOT be ALL-SYSTEMS.MCAST.NET (224.0.0.1) for IPv4 and
All Nodes Address (FF02::1) for IPv6. It MAY also be ALL-
ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers Address
(FF02::2) for IPv6 if the routing protocol in use does not define a
more appropriate multicast address.
If the Previous-hop router for the mtrace2 Request is known for this 4.3.2. Source Address
request and the number of response blocks is less than the number
requested (i.e., the "# hops" field in the mtrace2 Query header), the
packet is sent to that router. If the Incoming Interface is known
but the Previous-hop router is not known, the packet is sent to an
appropriate multicast address on the Incoming Interface. The
appropriate multicast address may depend on the routing protocol in
use, MUST be a link-scoped group (i.e. 224/24 for IPv4, FF02::/16 for
IPv6), MUST NOT be ALL-SYSTEMS.MCAST.NET (224.0.0.1) for IPv4 and All
Nodes Address (FF02::1) for IPv6, and MAY be ALL-ROUTERS.MCAST.NET
(224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6 if the
routing protocol in use does not define a more appropriate group.
Otherwise, it is sent to the Mtrace2 Client Address in the header.
9.3.2. Source Address An Mtrace2 Request should be sent with the address of the Incoming
interface. However, if the Incoming interface is unnumbered, the
router can use one of its numbered interface address as the source
address.
An mtrace2 Request should be sent with the address of the router's 4.3.3. Appending Standard Response Block
reception interface. However, if the router's interface address is
unnumbered, the router can use one of its numbered interface address
as the source address.
When the REACHED_GW code is noted, the router sends back the mtrace2 An Mtrace2 Request MUST be sent upstream towards the source or the RP
Reply as in Section 9.4. In addition to that, it must continue the after appending a Standard Response Block to the end of the received
mtrace2 Query by proxying the original querier as in Section 9.5. Mtrace2 Request. The Standard Response Block includes the multicast
states and statistics information of the router described in
Section 3.2.5.
When the NO_SPACE error occurs, the router sends back the mtrace2 If appending the Standard Response Block would make the Mtrace2
Reply with contained data and the NO_SPACE error code as in Request packet longer than the MTU of the Incoming Interface, or, in
Section 9.4, and continues the mtrace2 Query by sending an mtrace2 the case of IPv6, longer than 1280 bytes, the router MUST change the
Request containing the same mtrace2 Query header and its standard and Forwarding Code in the last Standard Response Block of the received
augmented response blocks. The corresponding augmented response Mtrace2 Request into NO_SPACE. The router then turns the Request
block type is "# Mtrace2 Response Blocks Returned" described in into a Reply, and sends the Reply as described in Section 4.4.
Section 8.
9.4. Sending Mtrace2 Reply The router will continue with a new Request by copying from the old
Request excluding all the response blocks, followed by the previously
prepared Standard Response Block, and an Augmented Response Block
with Augmented Response Type of 0x01 and the number of the returned
Standard Response Blocks as the value. The new Request is then
forwarded upstream.
9.4.1. Destination Address 4.4. Sending Mtrace2 Reply
An mtrace2 Reply must be sent to the address specified in the Mtrace2 An Mtrace2 Reply MUST be returned to the client by a router if the
Client Address field in the mtrace2 Query header. total number of the traced routers is equal to the # Hops in the
Request. The total number of the traced routers is the sum of the
Standard Response Blocks in the Request (including the one just
added) and the number of the returned blocks, if any.
9.4.2. Source Address 4.4.1. Destination Address
An mtrace2 Reply should be sent with the address of the router's An Mtrace2 Reply MUST be sent to the address specified in the Mtrace2
reception interface. However, if the router's interface address is Client Address field in the Mtrace2 Request.
4.4.2. Source Address
An Mtrace2 Reply SHOULD be sent with the address of the router's
Outgoing interface. However, if the Outgoing interface address is
unnumbered, the router can use one of its numbered interface address unnumbered, the router can use one of its numbered interface address
as the source address. as the source address.
9.5. Proxying Mtrace2 Query 4.4.3. Appending Standard Response Block
When a gateway (e.g., a NAT or firewall) that needs to block unicast An Mtrace2 Reply MUST be sent with the prepared Standard Response
packets to the mtrace2 querier or hide information between the Block appended at the end of the received Mtrace2 Request except in
gateway and the mtrace2 querier receives mtrace2 Query from an the case of NO_SPACE forwarding code.
adjacent host or mtrace2 Request from an adjacent router, it sends
back the mtrace2 Reply with contained data and the REACHED_GW code to
the address specified in the Mtrace2 Client Address field in the
mtrace2 Query header.
At the same time, the gateway prepares a new mtrace2 Query message. 4.5. Proxying Mtrace2 Query
The gateway uses the original mtrace2 Query header as the base for
the new mtrace2 Query; it sets the Mtrace2 Client Address to its
Incoming Interface address and the Client Port # to its own port
(which may be the same as the mtrace2 port as the gateway is
listening on that port), and decreases # hops according to the number
of standard response blocks in the returned mtrace2 Reply from the
gateway. The mtrace2 Query message is sent to the previous-hop
router or to an appropriate multicast address on the Incoming
Interface.
When the gateway receives the mtrace2 Reply from the first-hop router When a gateway (e.g., a NAT or firewall), which needs to block
or any intermediate router, it MUST forward the mtrace2 Reply back to unicast packets to the Mtrace2 client, or hide information between
the mtrace2 querier with the original mtrace2 Query header. the gateway and the Mtrace2 client, receives an Mtrace2 Query from an
adjacent host or Mtrace2 Request from an adjacent router, it appends
a Standard Response Block with REACHED_GW as the Forwarding Code, and
turns the Query or Request as a Reply, and sends the Reply back to
the client.
9.6. Hiding Information At the same time, the gateway originates a new Mtrace2 Query message
by copying the original Mtrace2 header (the Query or Request without
any of the response blocks), and makes the changes as follows:
o sets the RPF interface's address as the Mtrace2 Client Address;
o uses its own port number as the Client Port #; and,
o decreases # Hops by the number of the Standard Response Block that
was just returned as a Reply.
The new Mtrace2 Query message is then sent to the upstream router or
to an appropriate multicast address on the RPF interface.
When the gateway receives an Mtrace2 Reply whose Query ID matches the
one in the original Mtrace2 header, it MUST relay the Mtrace2 Reply
back to the Mtrace2 client by replacing the Reply's header with the
original Mtrace2 header. If the gateway does not receive the
corresponding Mtrace2 Reply within the [Mtrace Reply Timeout] period
(see Section 5.8.4), then it silently discards the original Mtrace2
Query or Request message, and terminates the trace.
4.6. Hiding Information
Information about a domain's topology and connectivity may be hidden Information about a domain's topology and connectivity may be hidden
from mtrace2 Requests. The INFO_HIDDEN forwarding code may be used from the Mtrace2 Requests. The Forwarding Code of INFO_HIDDEN may be
to note that, for example, the incoming interface address and packet used to note that. For example, the incoming interface address and
count are for the entrance to the domain and the outgoing interface packet count on the ingress router of a domain, and the outgoing
address and packet count are the exit from the domain by specifying interface address and packet count on the egress router of the domain
"all 1". The source-group packet count (Section 6.8 and Section 7.9) can be specified as all 1's. Additionally, the source-group packet
is from router, but may be "all 1" if it is hidden. count (see Section 3.2.5 and Section 3.2.6) within the domain may be
all 1's if it is hidden.
10. Client Behavior 5. Client Behavior
10.1. Sending Mtrace2 Query This section describes the behavior of an Mtrace2 client in details.
10.1.1. Destination Address 5.1. Sending Mtrace2 Query
Mtrace2 Query packet can be sent to the ALL-ROUTERS.MCAST.NET An Mtrace2 client initiates an Mtrace2 Query by sending the Query to
(224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6. This the LHR of interest.
will ensure that the packet is received by the last-hop router on the
subnet. Otherwise, if the proper last-hop router is known for the
mtrace2 destination, the Query is unicasted to that router.
See also Section 10.4 on determining the last-hop router. 5.1.1. Destination Address
10.1.2. Source Address If an Mtrace2 client knows the proper LHR, it unicasts an Mtrace2
Query packet to that router; otherwise, it MAY send the Mtrace2 Query
packet to the ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All
Routers Address (FF02::2) for IPv6. This will ensure that the packet
is received by the LHR on the subnet.
An mtrace2 Query must be sent with the address of the mtrace2 See also Section 5.4 on determining the LHR.
querier's reception interface, which would be the Mtrace2 Client
Address.
10.2. Determining the Path 5.1.2. Source Address
The client could send a small number of initial query messages with a An Mtrace2 Query MUST be sent with the client's interface address,
large "# hops" field, in order to try to trace the full path. If which would be the Mtrace2 Client Address.
this attempt fails, one strategy is to perform a linear search (as
the traditional unicast traceroute program does); set the "# hops"
field to 1 and try to get a Reply, then 2, and so on. If no Reply is
received at a certain hop, the hop count can continue past the non-
responding hop, in the hopes that further hops may respond. These
attempts should continue until a user-defined timeout has occurred.
See also Section 10.6 on receiving the results of a trace. 5.2. Determining the Path
10.3. Collecting Statistics An Mtrace2 client could send an initial Query messages with a large #
Hops, in order to try to trace the full path. If this attempt fails,
one strategy is to perform a linear search (as the traditional
unicast traceroute program does); set the # Hops field to 1 and try
to get a Reply, then 2, and so on. If no Reply is received at a
certain hop, the hop count can continue past the non-responding hop,
in the hopes that further hops may respond. These attempts should
continue until the [Mtrace Reply Timeout] timeout has occurred.
See also Section 5.6 on receiving the results of a trace.
5.3. Collecting Statistics
After a client has determined that it has traced the whole path or as After a client has determined that it has traced the whole path or as
much as it can expect to (see Section 10.7), it might collect much as it can expect to (see Section 5.8), it might collect
statistics by waiting a short time and performing a second trace. If statistics by waiting a short time and performing a second trace. If
the path is the same in the two traces, statistics can be displayed the path is the same in the two traces, statistics can be displayed
as described in Section 12.3 and Section 12.4. as described in Section 7.3 and Section 7.4.
10.4. Last Hop Router 5.4. Last Hop Router (LHR)
The mtrace2 querier may not know which is the last-hop router, or The Mtrace2 client may not know which is the last-hop router, or that
that router may be behind a firewall that blocks unicast packets but router may be behind a firewall that blocks unicast packets but
passes multicast packets. In these cases, the mtrace2 Request should passes multicast packets. In these cases, the Mtrace2 Request should
be multicasted to ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All be multicasted to ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All
Routers Address (FF02::2) for IPv6. All routers except the correct Routers Address (FF02::2) for IPv6. All routers except the correct
last-hop router SHOULD ignore any mtrace2 Request received via last-hop router SHOULD ignore any Mtrace2 Request received via
multicast. multicast.
10.5. First Hop Router 5.5. First Hop Router (FHR)
The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default
multicast group for old IPv4 mtrace (v1) responses, in order to multicast group for old IPv4 mtrace (v1) responses, in order to
support mtrace queriers that are not unicast reachable from the support mtrace clients that are not unicast reachable from the first-
first-hop router. However, mtrace2 does not reserve any IPv4/IPv6 hop router. Mtrace2, however, does not require any IPv4/IPv6
multicast addresses for mtrace2 Replies. Every mtrace2 Reply is sent multicast addresses for the Mtrace2 Replies. Every Mtrace2 Reply is
to the unicast address specified in the Mtrace2 Client Address field sent to the unicast address specified in the Mtrace2 Client Address
of the mtrace2 Query header. field of the Mtrace2 Reply.
10.6. Broken Intermediate Router 5.6. Broken Intermediate Router
A broken intermediate router might simply not understand mtrace2 A broken intermediate router might simply not understand Mtrace2
packets, and drop them. The querier would then get no Reply at all packets, and drop them. The Mtrace2 client will get no Reply at all
from its mtrace2 Requests. It should then perform a hop-by-hop as a result. It should then perform a hop-by-hop search by setting
search by setting the number of hops field until it gets a Reply the # Hops field until it gets an Mtrace2 Reply. The client may use
(both linear and binary search are options, but binary is likely to linear or binary search; however, the latter is likely to be slower
be slower because a failure requires waiting for a timeout). because a failure requires waiting for the [Mtrace Reply Timeout]
period.
10.7. Mtrace2 Termination 5.7. Non-Supported Router
When a non-supported router receives an Mtrace2 Query or Request
message whose destination address is a multicast address, the router
will silently discard the message.
When the router receives an Mtrace2 Query which is destined to
itself, the router would return an ICMP port unreachable to the
Mtrace2 client. On the other hand, when the router receives an
Mtrace2 Request which is destined to itself, the router would return
an ICMP port unreachable to its adjacent router from which the
Request receives. Therefore, the Mtrace2 client needs to terminate
the trace when the [Mtrace Reply Timeout] timeout has occurred, and
may then issue another Query with a lower number of # Hops.
5.8. Mtrace2 Termination
When performing an expanding hop-by-hop trace, it is necessary to When performing an expanding hop-by-hop trace, it is necessary to
determine when to stop expanding. determine when to stop expanding.
10.7.1. Arriving at source 5.8.1. Arriving at Source
A trace can be determined to have arrived at the source if the A trace can be determined to have arrived at the source if the
Incoming Interface of the last router in the trace is non-zero, but Incoming Interface of the last router in the trace is non-zero, but
the Previous-hop router is zero. the Upstream Router is zero.
10.7.2. Fatal error 5.8.2. Fatal Error
A trace has encountered a fatal error if the last Forwarding Error in A trace has encountered a fatal error if the last Forwarding Error in
the trace has the 0x80 bit set. the trace has the 0x80 bit set.
10.7.3. No previous hop 5.8.3. No Upstream Router
A trace can not continue if the last Previous-hop in the trace is set A trace can not continue if the last Upstream Router in the trace is
to 0. set to 0.
10.7.4. Traceroute shorter than requested 5.8.4. Reply Timeout
If the trace that is returned is shorter than requested (i.e. the This document defines the [Mtrace Reply Timeout] value, which is used
number of response blocks is smaller than the "# hops" field), the to time out an Mtrace2 Reply as seen in Section 4.5, Section 5.2, and
trace encountered an error and could not continue. Section 5.7. The default [Mtrace Reply Timeout] value is 10
(seconds), and can be manually changed on the Mtrace2 client and
routers.
10.8. Continuing after an error 5.9. Continuing after an Error
When the NO_SPACE error occurs, as described in Section 9.3, the When the NO_SPACE error occurs, as described in Section 4.2, a router
multicast routers sends back the mtrace2 Reply to the address will send back an Mtrace2 Reply to the Mtrace2 client, and continue
specified in the Mtrace2 Client Address field in the mtrace2 Query with a new Request (see Section 4.3.3). In which case, the Mtrace2
header. In this case, the mtrace2 client may receive multiple client may receive multiple Mtrace2 Replies from different routers
mtrace2 Replies from different routers (along the path). After the along the path. When this happens, the client MUST treat them as a
client receives multiple mtrace2 Reply messages, it integrates (i.e. single Mtrace2 Reply message.
constructs) them as a single mtrace2 Reply message.
If a trace times out, it is likely to be because a router in the If a trace times out, it is very likely that a router in the middle
middle of the path does not support mtrace2. That router's address of the path does not support Mtrace2. That router's address will be
will be in the Previous-hop router field of the last entry in the in the Upstream Router field of the last Standard Response Block in
last response packet received. A client may be able to determine the last received Reply. A client may be able to determine (via
(via mrinfo or SNMP [11][13]) a list of neighbors of the non- mrinfo or SNMP [11][10]) a list of neighbors of the non-responding
responding router. If desired, each of those neighbors could be router. If desired, each of those neighbors could be probed to
probed to determine the remainder of the path. Unfortunately, this determine the remainder of the path. Unfortunately, this heuristic
heuristic may end up with multiple paths, since there is no way of may end up with multiple paths, since there is no way of knowing what
knowing what the non-responding router's algorithm for choosing a the non-responding router's algorithm for choosing an upstream router
previous-hop router is. However, if all paths but one flow back is. However, if all paths but one flow back towards the non-
towards the non-responding router, it is possible to be sure that responding router, it is possible to be sure that this is the correct
this is the correct path. path.
11. Protocol-Specific Considerations 6. Protocol-Specific Considerations
11.1. PIM-SM This section describes the Mtrace2 behavior with the present of
different multicast protocols.
When an mtrace2 reaches a PIM-SM RP and the RP does not forward the 6.1. PIM-SM
When an Mtrace2 reaches a PIM-SM RP, and the RP does not forward the
trace on, it means that the RP has not performed a source-specific trace on, it means that the RP has not performed a source-specific
join so there is no more state to trace. However, the path that join so there is no more state to trace. However, the path that
traffic would use if the RP did perform a source-specific join can be traffic would use if the RP did perform a source-specific join can be
traced by setting the trace destination to the RP, the trace source traced by setting the trace destination to the RP, the trace source
to the traffic source, and the trace group to 0. This trace Query to the traffic source, and the trace group to 0. This Mtrace2 Query
may be unicasted to the RP. may be unicasted to the RP.
11.2. Bi-Directional PIM 6.2. Bi-Directional PIM
Bi-directional PIM [7] is a variant of PIM-SM that builds bi- Bi-directional PIM [5] is a variant of PIM-SM that builds bi-
directional shared trees connecting multicast sources and receivers. directional shared trees connecting multicast sources and receivers.
Along the bi-directional shared trees, multicast data is natively Along the bi-directional shared trees, multicast data is natively
forwarded from sources to the RPA (Rendezvous Point Address) and from forwarded from the sources to the Rendezvous Point Link (RPL), and
the RPA to receivers without requiring source-specific state. In from which, to receivers without requiring source-specific state. In
contrast to PIM-SM, RP always has the state to trace. contrast to PIM-SM, Bi-directional PIM always has the state to trace.
A Designated Forwarder (DF) for a given RPA is in charge of A Designated Forwarder (DF) for a given Rendezvous Point Address
forwarding downstream traffic onto its link, and forwarding upstream (RPA) is in charge of forwarding downstream traffic onto its link,
traffic from its link towards the RPL (Rendezvous Point Link) that and forwarding upstream traffic from its link towards the RPL that
the RPA belongs to. Hence mtrace2 reports DF addresses or RPA along the RPA belongs to. Hence Mtrace2 Reply reports DF addresses or RPA
the path. along the path.
11.3. PIM-DM 6.3. PIM-DM
Routers running PIM Dense Mode [15] do not know the path packets Routers running PIM Dense Mode [13] do not know the path packets
would take unless traffic is flowing. Without some extra protocol would take unless traffic is flowing. Without some extra protocol
mechanism, this means that in an environment with multiple possible mechanism, this means that in an environment with multiple possible
paths with branch points on shared media, mtrace2 can only trace paths with branch points on shared media, Mtrace2 can only trace
existing paths, not potential paths. When there are multiple existing paths, not potential paths. When there are multiple
possible paths but the branch points are not on shared media, the possible paths but the branch points are not on shared media, the
previous hop router is known, but the last-hop router may not know upstream router is known, but the LHR may not know that it is the
that it is the appropriate last hop. appropriate last hop.
When traffic is flowing, PIM Dense Mode routers know whether or not When traffic is flowing, PIM Dense Mode routers know whether or not
they are the last-hop forwarder for the link (because they won or they are the LHR for the link (because they won or lost an Assert
lost an Assert battle) and know who the previous hop is (because it battle) and know who the upstream router is (because it won an Assert
won an Assert battle). Therefore, mtrace2 is always able to follow battle). Therefore, Mtrace2 is always able to follow the proper path
the proper path when traffic is flowing. when traffic is flowing.
11.4. IGMP/MLD Proxy
When an mtrace2 Query packet reaches an incoming interface of IGMP/ 6.4. IGMP/MLD Proxy
MLD Proxy [8], it puts a WRONG_IF (0x01) value in Forwarding Code of
mtrace2 standard response block (as in Section 6.14) and sends the
mtrace2 Reply back to the Mtrace2 Client Address. When an mtrace2
Query packet reaches an outgoing interface of IGMP/MLD proxy, it is
forwarded through its incoming interface towards the upstream router.
11.5. AMT When an IGMP/MLD Proxy [6] receives an Mtrace2 Query packet on an
incoming interface, it notes a WRONG_IF in the Forwarding Code of the
last Standard Response Block (see Section 3.2.5), and sends the
Mtrace2 Reply back to the Mtrace2 client. On the other hand, when an
Mtrace2 Query packet reaches an outgoing interface of the IGMP/MLD
proxy, it is forwarded onto its incoming interface towards the
upstream router.
AMT [9] provides the multicast connectivity to the unicast-only 7. Problem Diagnosis
inter-network. To do this, multicast packets being sent to or from a
site are encapsulated in unicast packets. When an mtrace2 Query
packet reaches an AMT pseudo-interface of an AMT gateway, the AMT
gateway encapsulats it to a particular AMT relay reachable across the
unicast-only infrastructure. Then the AMT relay decapsulates the
mtrace2 Query packet and forwards the mtrace2 Request to the
appropriate multicast router.
12. Problem Diagnosis This section describes different scenarios Mtrace2 can be used to
diagnose the multicast problems.
12.1. Forwarding Inconsistencies 7.1. Forwarding Inconsistencies
The forwarding error code can tell if a group is unexpectedly pruned The Forwarding Error code can tell if a group is unexpectedly pruned
or administratively scoped. or administratively scoped.
12.2. TTL or Hop Limit Problems 7.2. TTL or Hop Limit Problems
By taking the maximum of hops (from source + forwarding TTL (or hop By taking the maximum of hops from the source and forwarding TTL
limit) threshold) over all hops, it is possible to discover the TTL threshold over all hops, it is possible to discover the TTL or hop
or hop limit required for the source to reach the destination. limit required for the source to reach the destination.
12.3. Packet Loss 7.3. Packet Loss
By taking two traces, it is possible to find packet loss information By taking two traces, it is possible to find packet loss information
by comparing the difference in input packet counts to the difference by comparing the difference in input packet counts to the difference
in output packet counts for the specified source-group address pair in output packet counts for the specified source-group address pair
at the previous hop. On a point-to-point link, any difference in at the previous hop. On a point-to-point link, any difference in
these numbers implies packet loss. Since the packet counts may be these numbers implies packet loss. Since the packet counts may be
changing as the mtrace2 Query is propagating, there may be small changing as the Mtrace2 Request is propagating, there may be small
errors (off by 1 or 2 or more) in these statistics. However, these errors (off by 1 or 2 or more) in these statistics. However, these
errors will not accumulate if multiple traces are taken to expand the errors will not accumulate if multiple traces are taken to expand the
measurement period. On a shared link, the count of input packets can measurement period. On a shared link, the count of input packets can
be larger than the number of output packets at the previous hop, due be larger than the number of output packets at the previous hop, due
to other routers or hosts on the link injecting packets. This to other routers or hosts on the link injecting packets. This
appears as "negative loss" which may mask real packet loss. appears as "negative loss" which may mask real packet loss.
In addition to the counts of input and output packets for all In addition to the counts of input and output packets for all
multicast traffic on the interfaces, the response data includes a multicast traffic on the interfaces, the Standard Response Block
count of the packets forwarded by a node for the specified source- includes a count of the packets forwarded by a node for the specified
group pair. Taking the difference in this count between two traces source-group pair. Taking the difference in this count between two
and then comparing those differences between two hops gives a measure traces and then comparing those differences between two hops gives a
of packet loss just for traffic from the specified source to the measure of packet loss just for traffic from the specified source to
specified receiver via the specified group. This measure is not the specified receiver via the specified group. This measure is not
affected by shared links. affected by shared links.
On a point-to-point link that is a multicast tunnel, packet loss is On a point-to-point link that is a multicast tunnel, packet loss is
usually due to congestion in unicast routers along the path of that usually due to congestion in unicast routers along the path of that
tunnel. On native multicast links, loss is more likely in the output tunnel. On native multicast links, loss is more likely in the output
queue of one hop, perhaps due to priority dropping, or in the input queue of one hop, perhaps due to priority dropping, or in the input
queue at the next hop. The counters in the response data do not queue at the next hop. The counters in the Standard Response Block
allow these cases to be distinguished. Differences in packet counts do not allow these cases to be distinguished. Differences in packet
between the incoming and outgoing interfaces on one node cannot counts between the incoming and outgoing interfaces on one node
generally be used to measure queue overflow in the node. cannot generally be used to measure queue overflow in the node.
12.4. Link Utilization 7.4. Link Utilization
Again, with two traces, you can divide the difference in the input or Again, with two traces, you can divide the difference in the input or
output packet counts at some hop by the difference in time stamps output packet counts at some hop by the difference in time stamps
from the same hop to obtain the packet rate over the link. If the from the same hop to obtain the packet rate over the link. If the
average packet size is known, then the link utilization can also be average packet size is known, then the link utilization can also be
estimated to see whether packet loss may be due to the rate limit or estimated to see whether packet loss may be due to the rate limit or
the physical capacity on a particular link being exceeded. the physical capacity on a particular link being exceeded.
12.5. Time Delay 7.5. Time Delay
If the routers have synchronized clocks, it is possible to estimate If the routers have synchronized clocks, it is possible to estimate
propagation and queuing delay from the differences between the propagation and queuing delay from the differences between the
timestamps at successive hops. However, this delay includes control timestamps at successive hops. However, this delay includes control
processing overhead, so is not necessarily indicative of the delay processing overhead, so is not necessarily indicative of the delay
that data traffic would experience. that data traffic would experience.
13. IANA Considerations 8. IANA Considerations
The following new assignments can only be made via a Standards Action The following new assignments can only be made via a Standards Action
as specified in [4]. as specified in [7].
13.1. Forwarding Codes 8.1. Forwarding Codes
New Forwarding codes must only be created by an RFC that modifies New Forwarding Codes must only be created by an RFC that modifies
this document's Section 10, fully describing the conditions under this document's Section 3.2.5 and Section 3.2.6, fully describing the
which the new forwarding code is used. The IANA may act as a central conditions under which the new Forwarding Code is used. The IANA may
repository so that there is a single place to look up forwarding act as a central repository so that there is a single place to look
codes and the document in which they are defined. up Forwarding Codes and the document in which they are defined.
13.2. UDP Destination Port and IPv6 Address 8.2. UDP Destination Port
The IANA should allocate UDP destination port for multicast The IANA should allocate UDP destination port for Mtrace2 upon
traceroute version 2 upon publication of the first RFC. publication of the first RFC.
14. Security Considerations 9. Security Considerations
14.1. Topology Discovery This section addresses some of the security considerations related to
Mtrace2.
9.1. Addresses in Mtrace2 Header
An Mtrace2 header includes three addresses, source address, multicast
address, and Mtrace2 client address. These addresses MUST be
congruent with the definition defined in Section 3.2.1 and forwarding
Mtrace2 messages having invalid addresses MUST be prohibited. For
instance, if Mtrace2 Client Address specified in an Mtrace header is
a multicast address, then a router that receives the Mtrace2 message
MUST silently discard it.
9.2. Topology Discovery
Mtrace2 can be used to discover any actively-used topology. If your Mtrace2 can be used to discover any actively-used topology. If your
network topology is a secret, mtrace2 may be restricted at the border network topology is a secret, Mtrace2 may be restricted at the border
of your domain, using the ADMIN_PROHIB forwarding code. of your domain, using the ADMIN_PROHIB forwarding code.
14.2. Traffic Rates 9.3. Characteristics of Multicast Channel
Mtrace2 can be used to discover what sources are sending to what Mtrace2 can be used to discover what sources are sending to what
groups and at what rates. If this information is a secret, mtrace2 groups and at what rates. If this information is a secret, Mtrace2
may be restricted at the border of your domain, using the may be restricted at the border of your domain, using the
ADMIN_PROHIB forwarding code. ADMIN_PROHIB forwarding code.
14.3. Limiting Query/Request Rates 9.4. Limiting Query/Request Rates
Routers should limit mtrace2 Queries and Requests by ignoring the A router may limit Mtrace2 Queries and Requests by ignoring some of
received messages. Routers MAY randomly ignore the received messages the consecutive messages. The router MAY randomly ignore the
to minimize the processing overhead, i.e., to keep fairness in received messages to minimize the processing overhead, i.e., to keep
processing queries. The rate limit is left to the router's fairness in processing queries, or prevent traffic amplification.
implementation. The rate limit is left to the router's implementation.
15. Acknowledgements 9.5. Limiting Reply Rates
The proxying and NO_SPACE behaviors may result in one Query returning
multiple Reply messages. In order to prevent abuse, the routers in
the traced MAY need to rate-limit the Replies. The rate limit
function is left to the router's implementation.
10. Acknowledgements
This specification started largely as a transcription of Van This specification started largely as a transcription of Van
Jacobson's slides from the 30th IETF, and the implementation in Jacobson's slides from the 30th IETF, and the implementation in
mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve
Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original
multicast traceroute client, mtrace (version 1), has been implemented multicast traceroute client, mtrace (version 1), has been implemented
by Ajit Thyagarajan, Steve Casner and Bill Fenner. The idea of the by Ajit Thyagarajan, Steve Casner and Bill Fenner. The idea of the
"S" bit to allow statistics for a source subnet is due to Tom "S" bit to allow statistics for a source subnet is due to Tom
Pusateri. Pusateri.
For the mtrace version 2 specification, extensive comments were For the Mtrace version 2 specification, the authors would like to
received from Ronald Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Pekka give special thanks to Tatsuya Jinmei, Bill Fenner, and Steve Casner.
Savola, Shinsuke Suzuki, Dave Thaler, Achmad Husni Thamrin, and Cao Also, extensive comments were received from David L. Black, Ronald
Wei. Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Robert W. Kebler, Heidi Ou,
Pekka Savola, Shinsuke Suzuki, Dave Thaler, Achmad Husni Thamrin, and
Cao Wei.
16. References 11. References
16.1. Normative References 11.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to indicate requirement [1] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[2] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", RFC 2119, March 1997. levels", RFC 2119, March 1997.
[2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) [3] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998. Specification", RFC 2460, December 1998.
[3] Hinden, R. and S. Deering, "IP Version 6 Addressing [4] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998. Architecture", RFC 4291, February 2006.
[4] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 2434, October 1998.
[5] Braden, B., Borman, D., and C. Partridge, "Computing the
Internet Checksum", RFC 1071, September 1988.
[6] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[7] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, [5] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-PIM)", "Bidirectional Protocol Independent Multicast (BIDIR-PIM)",
RFC 5015, October 2007. RFC 5015, October 2007.
[8] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet [6] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet
Group Management Protocol (IGMP) / Multicast Listener Discovery Group Management Protocol (IGMP) / Multicast Listener Discovery
(MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")",
RFC 4605, August 2006. RFC 4605, August 2006.
[9] Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T. [7] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Pusateri, "Automatic IP Multicast Without Explicit Tunnels Considerations Section in RFCs", RFC 5226, May 2008.
(AMT)", draft-ietf-mboned-auto-multicast-08.txt (work in
progress), October 2007.
16.2. Informative References 11.2. Informative References
[10] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. [8] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version 3", Thyagarajan, "Internet Group Management Protocol, Version 3",
RFC 3376, October 2002. RFC 3376, October 2002.
[11] Draves, R. and D. Thaler, "Default Router Preferences and More- [9] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB",
Specific Routes", RFC 4191, November 2005.
[12] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB",
RFC 2863, June 2000. RFC 2863, June 2000.
[13] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB", [10] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB",
RFC 5132, December 2007. RFC 5132, December 2007.
[14] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. Pignataro, [11] Draves, R. and D. Thaler, "Default Router Preferences and More-
Specific Routes", RFC 4191, November 2005.
[12] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. Pignataro,
"The Generalized TTL Security Mechanism (GTSM)", RFC 5082, "The Generalized TTL Security Mechanism (GTSM)", RFC 5082,
October 2007. October 2007.
[15] Adams, A., Nicholas, J., and W. Siadak, "Protocol Independent [13] Adams, A., Nicholas, J., and W. Siadak, "Protocol Independent
Multicast - Dense Mode (PIM-DM): Protocol Specification Multicast - Dense Mode (PIM-DM): Protocol Specification
(Revised)", RFC 3973, January 2005. (Revised)", RFC 3973, January 2005.
Authors' Addresses Authors' Addresses
Hitoshi Asaeda Hitoshi Asaeda
Keio University National Institute of Information and Communications Technology
Graduate School of Media and Governance 4-2-1 Nukui-Kitamachi
Fujisawa, Kanagawa 252-0882 Koganei, Tokyo 184-8795
Japan Japan
Email: asaeda@wide.ad.jp Email: asaeda@nict.go.jp
URI: http://www.sfc.wide.ad.jp/~asaeda/
Tatuya Jinmei
Internet Systems Consortium
Redwood City, CA 94063
US
Email: Jinmei_Tatuya@isc.org
William C. Fenner
Arastra, Inc.
Menlo Park, CA 94025
US
Email: fenner@fenron.net
Stephen L. Casner WeeSan Lee (editor)
Packet Design, Inc. Juniper Networks, Inc.
Palo Alto, CA 94304 1194 North Mathilda Avenue
Sunnyvale, CA 94089-1206
US US
Email: casner@packetdesign.com Email: weesan@juniper.net
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