wdiff draft-ietf-mboned-mtrace-v2-08.txt draft-ietf-mboned-mtrace-v2-09.txt

MBONED Working Group H. Asaeda
Internet-Draft Keio University NICT
Intended status: Standards Track T. Jinmei
Expires: July 11, 2011 ISC W. Fenner
Arastra, Inc.
S. Casner
Packet Design, Lee, Ed.
Expires: April 25, 2013 Juniper Networks, Inc.
January 7, 2011
October 22, 2012

Mtrace Version 2: Traceroute Facility for IP Multicast
draft-ietf-mboned-mtrace-v2-08
draft-ietf-mboned-mtrace-v2-09

Abstract

This document describes the IP multicast traceroute facility. facility, named
Mtrace version 2 (Mtrace2). Unlike unicast traceroute, multicast traceroute Mtrace2
requires special implementations on the part of routers. This
specification describes the required functionality in multicast
routers, as well as how
management applications can use the router functionality. an Mtrace2 client invokes a query and
receives a reply.

Status of this Memo

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Overview . . . . 6
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 9
4. 6
3. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. 7
3.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 10
4.2. 8
3.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 10
5. 8
3.2.1. Mtrace2 Query Header . . . . . . . . . . . . . . . . . . . . 9
3.2.2. Mtrace2 Extended Query Block . . . . 12
5.1. # hops: 8 bits . . . . . . . . . 10
3.2.3. Mtrace2 Request . . . . . . . . . . . . . . 12
5.2. Multicast Address . . . . . 11
3.2.4. Mtrace2 Reply . . . . . . . . . . . . . . . . 13
5.3. Source Address . . . . 11
3.2.5. IPv4 Mtrace2 Standard Response Block . . . . . . . . . 12
3.2.6. IPv6 Mtrace2 Standard Response Block . . . . . . . . . 13
5.4. 16
3.2.7. Mtrace2 Client Address Augmented Response Block . . . . . . . . . . . 19
4. Router Behavior . . . . . . . 13
5.5. Query ID: 16 bits . . . . . . . . . . . . . . . . 20
4.1. Receiving Mtrace2 Query . . . . 13
5.6. Client Port # . . . . . . . . . . . . . 20
4.1.1. Query Packet Verification . . . . . . . . . 13
6. IPv4 Mtrace2 Standard Response Block . . . . . 20
4.1.2. Query Normal Processing . . . . . . . . 14
6.1. MBZ: 8 bit . . . . . . . 21
4.2. Receiving Mtrace2 Request . . . . . . . . . . . . . . . . 21
4.2.1. Request Packet Verification . 14
6.2. Query Arrival Time: 32 bits . . . . . . . . . . . . 21
4.2.2. Request Normal Processing . . . 14
6.3. Incoming Interface Address: 32 bits . . . . . . . . . . . 15
6.4. Outgoing Interface Address: 32 bits 22
4.3. Forwarding Mtrace2 Request . . . . . . . . . . . 15
6.5. Previous-Hop Router Address: 32 bits . . . . . 23
4.3.1. Destination Address . . . . . . 15
6.6. Input packet count on incoming interface: 64 bits . . . . 15
6.7. Output packet count on outgoing interface: 64 bits . . . . 16
6.8. Total number of packets for this source-group pair: 64
bits . . . . 24
4.3.2. Source Address . . . . . . . . . . . . . . . . . . . . 24
4.3.3. Appending Standard Response Block . . . 16
6.9. Rtg Protocol: 16 bits . . . . . . . 24
4.4. Sending Mtrace2 Reply . . . . . . . . . . . 16
6.10. Multicast Rtg Protocol: 16 bits . . . . . . . 24
4.4.1. Destination Address . . . . . . 16
6.11. Fwd TTL: 8 bits . . . . . . . . . . . 25
4.4.2. Source Address . . . . . . . . . . 16
6.12. S: 1 bit . . . . . . . . . . 25
4.4.3. Appending Standard Response Block . . . . . . . . . . 25
4.5. Proxying Mtrace2 Query . . . . . 16
6.13. Src Mask: 7 bits . . . . . . . . . . . . . 25
4.6. Hiding Information . . . . . . . . 17
6.14. Forwarding Code: 8 bits . . . . . . . . . . . . 26
5. Client Behavior . . . . . 17
7. IPv6 Mtrace2 Standard Response Block . . . . . . . . . . . . . 19
7.1. MBZ: 8 bit . . . . . 26
5.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 26
5.1.1. Destination Address . 19
7.2. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 20
7.3. Incoming Interface ID: 32 bits . 26
5.1.2. Source Address . . . . . . . . . . . . . 20
7.4. Outgoing Interface ID: 32 bits . . . . . . . 26
5.2. Determining the Path . . . . . . . 20
7.5. Local Address . . . . . . . . . . . . 26
5.3. Collecting Statistics . . . . . . . . . . 20
7.6. Remote Address . . . . . . . . 27
5.4. Last Hop Router (LHR) . . . . . . . . . . . . . . 20
7.7. Input packet count on incoming interface . . . . 27
5.5. First Hop Router (FHR) . . . . . 20
7.8. Output packet count on outgoing interface . . . . . . . . 21
7.9. Total number of packets for this source-group pair . . . . 21
7.10. Rtg Protocol: 16 bits . 27
5.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 27
5.7. Non-Supported Router . 21
7.11. Multicast Rtg Protocol: 16 bits . . . . . . . . . . . . . 21
7.12. S: 1 bit . . . . . 28
5.8. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 28
5.8.1. Arriving at Source . 21
7.13. Src Prefix Len: 8 bits . . . . . . . . . . . . . . . . . 28
5.8.2. Fatal Error . 21
7.14. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 21
8. Mtrace2 Augmented Response Block . . . 28
5.8.3. No Upstream Router . . . . . . . . . . . . 22
9. Router Behavior . . . . . . 28
5.8.4. Reply Timeout . . . . . . . . . . . . . . . . . 23
9.1. Receiving Mtrace2 Query . . . 28
5.9. Continuing after an Error . . . . . . . . . . . . . . 23
9.1.1. Packet Verification . . 28
6. Protocol-Specific Considerations . . . . . . . . . . . . . . . 23
9.1.2. Normal Processing . . . . . 29
6.1. PIM-SM . . . . . . . . . . . . . 23
9.1.3. Mtrace2 Query Received by Non-Supported Router . . . . 23
9.2. Receiving Mtrace2 Request . . . . . . . . . 29
6.2. Bi-Directional PIM . . . . . . . 24
9.2.1. Packet Verification . . . . . . . . . . . . . 29
6.3. PIM-DM . . . . 24
9.2.2. Normal Processing . . . . . . . . . . . . . . . . . . 24
9.2.3. Mtrace2 Request Received by Non-Supported Router . . . 26
9.3. Forwarding Mtrace2 Request . 30
6.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . 26
9.3.1. Destination Address . . . . . . . 30
7. Problem Diagnosis . . . . . . . . . . 26
9.3.2. Source Address . . . . . . . . . . . . 30
7.1. Forwarding Inconsistencies . . . . . . . . 26
9.4. Sending Mtrace2 Reply . . . . . . . . 30
7.2. TTL or Hop Limit Problems . . . . . . . . . . 27
9.4.1. Destination Address . . . . . . 30
7.3. Packet Loss . . . . . . . . . . . 27
9.4.2. Source Address . . . . . . . . . . . . 30
7.4. Link Utilization . . . . . . . . 27
9.5. Proxying Mtrace2 Query . . . . . . . . . . . . . 31
7.5. Time Delay . . . . . 27
9.6. Hiding Information . . . . . . . . . . . . . . . . . . . 31
8. IANA Considerations . 28
10. Client Behavior . . . . . . . . . . . . . . . . . . . . 32
8.1. Forwarding Codes . . . 29
10.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 29
10.1.1. 32
8.2. UDP Destination Address . . . . . . . . . . . . . . . . . 29
10.1.2. Source Address . . . . . . . . . . . . . . . . . . . . 29
10.2. Determining the Path . . Port . . . . . . . . . . . . . . . . . 29
10.3. Collecting Statistics . . 32
9. Security Considerations . . . . . . . . . . . . . . . . 29
10.4. Last Hop Router . . . 32
9.1. Addresses in Mtrace2 Header . . . . . . . . . . . . . . . 32
9.2. Topology Discovery . . . 29
10.5. First Hop Router . . . . . . . . . . . . . . . . . 32
9.3. Characteristics of Multicast Channel . . . . 30
10.6. Broken Intermediate Router . . . . . . . 32
9.4. Limiting Query/Request Rates . . . . . . . . . 30
10.7. Mtrace2 Termination . . . . . . 33
9.5. Limiting Reply Rates . . . . . . . . . . . . . 30
10.7.1. Arriving at source . . . . . . 33
10. Acknowledgements . . . . . . . . . . . . 30
10.7.2. Fatal error . . . . . . . . . . . 33
11. References . . . . . . . . . . 30
10.7.3. No previous hop . . . . . . . . . . . . . . . . 33
11.1. Normative References . . . 30
10.7.4. Traceroute shorter than requested . . . . . . . . . . 30
10.8. Continuing after an error . . . . . . 33
11.2. Informative References . . . . . . . . . . 31
11. Protocol-Specific Considerations . . . . . . . . 34
Authors' Addresses . . . . . . . 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 34

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
mtrace
Mtrace version 2 or mtrace2. Mtrace2 which allows the tracing of an IP
multicast routing paths. path. Mtrace2 is usually initiated from a Mtrace2
client towards a specified source, or a Rendezvous Point (RP) if no
source address is specified. RP is a special router where the source
and receiver meet in PIM-SM [1]. Moreover, Mtrace2 provides
additional information
about such as the packet rates and losses, or as well
as other diagnosis information. For
instance, mtrace2 is Especially, Mtrace2 can be used for
the following purposes. purposes:

o To trace the path that a packet would take from some a source to
some destination. a
receiver.

o To isolate packet loss problems (e.g., congestion).

o To isolate configuration problems (e.g., TTL threshold).

Figure 1 shows a typical case on how Mtrace2 consists of the client and router programs. The mtrace2
client program is invoked from somewhere in used. FHR represents
the multicast tree, on a
host, first-hop router, or proxy such as IGMP/MLD proxy [8]. The LHR represents the last-hop router, and the
arrow lines represent the Mtrace2 messages that are sent from one
node invoking to another. The numbers before the program is called Mtrace2 messages represent
the mtrace2 client. sequence of the messages that would happen. Source, Receiver and
Mtrace2 client are typically a host on the Internet.

2. Request 2. Request
+----+ +----+
| | | |
v | v |
+--------+ +-----+ +-----+ +----------+
| Source |----| FHR |----- The mtrace2 Internet -----| LHR |----| Receiver |
+--------+ +-----+ | +-----+ +----------+
\ | ^
\ | /
\ | /
\ | /
3. Reply \ | / 1. Query
\ | /
\ | /
\ +---------+ /
v | Mtrace2 |/
| client program creates |
+---------+

Figure 1

When an Mtrace2 client initiates a multicast trace anywhere on the mtrace2
Internet, it sends an Mtrace2 Query message, which
includes packet to the LHR for a source and multicast address specified by
group and a source address. The LHR turns the client, Query packet into a
Request, appends a standard response block containing its interface
addresses and packet statistics to the Request packet, then forwards
the message packet towards the source. The Request packet is either
unicasted to its neighbor upstream router or proxy. This initiates
a trace of a multicast routing path from the client toward towards the
specified source, or multicasted
to the group if no source the upsteam router's IP address is specified, toward a core
router if such a router exists. not known. In the case of PIM-SM [6], the core
router is an RP maintaining the specified multicast address.

When a
similar fashion, each router or proxy receives an mtrace2 Query message and has along the
corresponding routing state regarding path to 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 appends a
standard response block to the query and forwards end of the Request toward the specified source or the core packet before
forwarding it to its upstream router. When a first-hop router or proxy (a single hop from the source
specified in the request) or the core router FHR receives an mtrace2
Query or the
Request message, packet, it appends its own standard response block, turns the router or proxy invokes
Request packet into a Reply, and unicasts the mtrace2
router program. The mtrace2 router program creates an mtrace2 Reply
message. back to the
Mtrace2 client.

The Mtrace2 Reply message may be returned before reaching the FHR if it
reaches the RP first, or a fatal error condition such as "no route"
is forwarded to encountered along the mtrace2 client, thus
completing path, or the mtrace2 Request. hop count is exceeded.

The mtrace2 Mtrace2 client program waits for the mtrace2 Mtrace2 Reply message and displays
the results. When not receiving an mtrace2 Mtrace2 Reply message does not come due to
network congestion, a broken router (see Section 10.6) 5.6), or a
non-responding non-
responding router (see Section 10.8), 5.7), the mtrace2 Mtrace2 client program
can may resend an mtrace2
another Mtrace2 Query with a lower hop count (see Section 5.1) 3.2.1), and
repeat the process until it receives an mtrace2 Mtrace2 Reply message. The mtrace2
details are Mtrace2 client should also be aware that the mtrace2 Query may
follow the control path on the routers, in specific, and it is outside the case scope of
this document.

Note that when a router's control plane and forwarding plane are not synchronized, e.g., a
buggy implementation. In this case, mtrace2 out
of sync, the Mtrace2 Requests will might be forwarded toward the specified source or based on the core router because control
states instead. In which case, the
router does traced path might not have any forwarding state for represent
the query.

The mtrace2 real path the data packets would follow.

Mtrace2 supports both IPv4 and IPv6 multicast traceroute
facility. The protocol design, concept, and program behavior are
same between IPv4 and IPv6 mtrace2. While the original IPv4
multicast traceroute, mtrace, IPv6. Unlike the previous version of
Mtrace, which implements its query and response messages are
implemented as IGMP messages [10], [8],
all mtrace2 Mtrace2 messages are carried
on UDP. The UDP-based. Although the packet formats of
IPv4 and IPv6 mtrace2 Mtrace2 are different because of the different address families, but
the syntax between them is similar.

2. Terminology

The

In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL
NOT","SHOULD", NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED","MAY", "RECOMMENDED", "MAY",
and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119 [1]. [2],
and indicate requirement levels for compliant Mtrace2
implementations.

2.1. Definitions

Since multicast traceroutes Mtrace2 Queries and Requests flow in the opposite direction to
the data flow, we refer to "upstream" and "downstream" with respect
to data, unless explicitly specified.

Incoming interface: interface
The interface on which traffic data is expected to arrive from the
specified source and group.

Outgoing interface: interface
The interface on to which traffic is forwarded data from the source or RP is expected to
transmit for the specified source and group toward the destination. group. It is also the
interface on which the
mtrace2 Query or Mtrace2 Request was will be received.

Previous-hop router:
The

Upstream router that is on the link attached
The router, connecting to the Incoming interface and of the current
router, which is responsible for forwarding traffic data for the specified
source and
group.

Last-hop router: group to the current router.

First-hop router (FHR)
The router that is on directly connected to the link attached source the Mtrace2
Query specifies.

Last-hop router (LHR)
The router that is directly connected to the Outgoing interface and receivers. It is
also the router that receives the mtrace2 Mtrace2 Query from the adjacent mtrace2 an Mtrace2
client.

Group state: state
It is the state in which a shared-tree protocol (e.g., protocol, such as PIM-SM [6])
running on a router chooses [1], uses
to choose the previous-hop upstream router toward towards the core
router or Rendezvous Point (RP) as its parent router. RP for the specified
group. In this state, source-specific state is not available for
the corresponding
multicast group address on the router.

Source-specific state: state
It is the state in which a routing protocol running on a router
chooses that is used to choose the path that would be followed towards the source
for a source-specific join.

ALL-[protocol]-ROUTERS.MCAST.NET: the specified source and group.

ALL-[protocol]-ROUTERS.MCAST.NET
It is a dedicated link-local multicast address for a multicast router routers to
communicate with other their adjacent routers that are working with running the same
routing protocol. For instance, the address of ALL-PIM-ROUTERS.MCAST.NET [6] ALL-PIM-
ROUTERS.MCAST.NET [1] is '224.0.0.13' for IPv4 and 'ff02::d' for
IPv6.

3. Overview

Given a multicast distribution tree, tracing from a source to a
multicast destination is hard, since you do not know down which
branch of Packet Formats

This section describes the multicast tree details of the destination lies. This means that
you have to flood packet formats for Mtrace2
messages.

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 whole tree to find unknown TLV. If the path from one source to
one destination. However, walking up length of a TLV exceeds
the tree from destination to
source is easy, as most existing multicast routing protocols know length specified in the
previous hop for each source. Tracing from destination to source can
involve only routers on TLV, the direct path.

The party requesting TLV SHOULD be accepted; however,
any additional data after the multicast traceroute sends a traceroute TLV SHOULD be ignored.

All Mtrace2 messages are UDP packets. For IPv4, Mtrace2 Query and
Request messages MUST NOT be fragmented. For IPv6, the packet to size
for the last-hop multicast router Mtrace2 messages MUST NOT exceed 1280 bytes, which is the
smallest MTU for an IPv6 interface [3]. The source port is uniquely
selected by the given multicast
address. local host operating system. The last-hop router turns destination port is
the Query into IANA reserved Mtrace2 port number (see Section 8). All Mtrace2
messages MUST have a Request packet
by changing the packet type valid UDP checksum.

Additionally, Mtrace2 supports both IPv4 and adding a response data block
containing its interface IPv6, but not mixed.
For example, if an Mtrace2 Query or Reply message arrives in as an
IPv4 packet, all addresses and packet statistics, and then
forwards specified in the Request packet via unicast Mtrace2 messages MUST be
IPv4 as well. Same rule applies to IPv6 Mtrace2 messages.

3.1. Mtrace2 TLV format

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 | Value .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type: 8 bits

Describes the router that the last-
hop router believes is the proper previous hop for format of the given source
and group. Each hop adds its response data to Value field. For all the end available
types, please see Section 3.2

Length: 16 bits

Length of Type, Length, and Value fields in octets. Minimum
length required is 6 octets. The maximum TLV length is not
defined; however the Request
packet, then unicast forwards it to entired Mtrace2 packet length should not
exceeed the previous hop. available MTU.

Value: variable length

The first-hop
router (the router that believes that packets from the source
originate format is based on one of its directly connected networks) changes the
packet type to indicate a Reply packet and sends the completed Reply
to Type value. The length of the mtrace2 client address specified value
field is Length field minus 3. All reserved fields in the Query header. The
Reply may Value
field MUST be returned before reaching the first-hop router if a fatal
error condition such transmitted as "no route" is encountered along the path zeros and ignored on receipt.

3.2. Defined TLVs

The following TLV Types are defined:

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

Each Mtrace2 message MUST begin with either a Query, Request or
hop count is exceeded.

Multicast traceroute uses any information available to it in Reply
TLV. The first TLV determines the
router to attempt to determine type of each Mtrace2 message.
Following this TLV, there can be a previous hop to forward sequence of optional Extended
Query Blocks. In the trace
towards. Multicast routing protocols vary in case of the type Request and amount of
state they keep; multicast traceroute endeavors to work with all of
them by using whatever Reply message, it is available. For example, if
then followed by a PIM-SM sequence of Standard Response Blocks, each from a
multicast router
is on the (*,G) tree, it chooses the parent path towards the RP as source or the
previous hop. RP. In these cases, no source/group-specific state is
available, but the path may still be traced.

4. Packet Formats

The mtrace2 message
case more information is carried as needed, a UDP packet. The destination
address of mtrace2 Query messages is either the last-hop router
unicast address or multicast address if the mtrace2 client does not
know the proper last-hop router address. The destination address of
mtrace2 Report messages is the address specified in Previous-Hop
Router Address field in the last appended mtrace2 Standard Response
Block, which is either the previous-hop router unicast address Block can be
followed by one or
multicast address. Detailed multiple Augmented Response Blocks.

We will describe each message type in Section 9.3. details in the next few
sections.

3.2.1. Mtrace2 message Query

An Mtrace2 query is encoded in TLV format. If usually originated by an implementation
receives a TLV whose length exceeds Mtrace2 client which
sends an Mtrace2 Query message to the TLV length specified in LHR. When tracing towards the
Length field,
source or the TLV SHOULD be accepted but any additional data
SHOULD be ignored. If an implementation receives a TLV whose type
value is unknown, RP, the intermediate routers MUST NOT modify the mtrace2 Query
message SHOULD be ignored and silently
dropped.

4.1. except the Type field.

An Mtrace2 TLV format 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 | Value .... # Hops |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type (8 bits)

Length (16 bits)

Value (variable length)

4.2. Defined TLVs

The following TLV Types are defined:

Figure 2

# Hops: 8 bits
This field specifies the maximum number of hops that the Mtrace2 Request
3
client wants to trace. If there are some error conditions in the
middle of the path that prevent an Mtrace2 Reply
4 Mtrace2 Standard Response Block
5 Mtrace2 Augmented Response Block

An mtrace2 message MUST contain exactly one from being
received by the client, the client MAY issues another Mtrace2
Query header. A
multicast router that sends an mtrace2 Request or with the lower number of hops until it receives a 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 from
the FHR.

Multicast Address: 32 bits or multiple Augmented Response
blocks.

The TLV type 128 bits
This field is defined specifies an IPv4 or IPv6 address, which can be either:

m-1: a multicast group address to be "0x1" and "0x2" for mtrace2
Queries and Requests, respectively. An mtrace2 message containing traced; or,

m-2: all 1's in case of IPv4 or the type "0x1" is an mtrace2 Query. It unspecified address (::) in
case of IPv6 if no group-specific information is sent by desired.

Source Address: 32 bits or 128 bits
This field specifies an mtrace2 querier
(i.e., IPv4 or IPv6 address, which can be either:

s-1: an mtrace2 client). It is changed unicast address of the source to "0x2" by be traced; or,

s-2: all 1's in case of IPv4 or the proper
last-hop router. The type field unspecified address (::) in
case of IPv6 if no source-specific information is changed to "0x3" when desired.
For example, the packet client is completed and sent as tracing a (*,g) group state.

Note that it is invalid to have a source-group combination of
(s-2, m-2). If a router receives such combination in an mtrace2 Reply from Mtrace2
Query, it MUST silently discard the first-hop router
to Query.

Mtrace2 Client Address: 32 bits or 128 bits
This field specifies the querier.

5. Mtrace2 Query Header

The mtrace2 supports both client's IPv4 address or IPv6
global address. This address MUST be a valid unicast address, and IPv6. If the mtrace2 Query
therefore, MUST NOT be all 1's or
Reply arrives in an IPv4 packet, all addresses specified in the
mtrace2 messages must be with IPv4 addresses. unspecified address. The mtrace2 message
Mtrace2 Reply will be sent to this address.

Query ID: 16 bits
This field is carried used as a UDP packet. The UDP source port
is uniquely selected by unique identifier for this Mtrace2 Query
so that duplicate or delayed Reply messages may be detected.

Client Port #: 16 bits
This field specifies the local host operating system. The UDP destination port is the IANA reserved mtrace2 UDP port number (see
Section 13). The UDP checksum MUST for receiving
the Mtrace2 Reply packet.

3.2.2. Mtrace2 Extended Query 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 valid interested in mtrace2 messages.

The mtrace2 message includes tracing
the common mtrace2 Query header 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
follows. the Value for an Extended Query Type (see below). The header Extended
Query Type is only filled in by the originator of extensible and the
mtrace2 Query; intermediate routers MUST NOT modify any behavior of the
fields. new types will be
addressed by seperate documents.

The Mtrace2 Extended Query Block is formatted 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
+-+-+-+-+-+-+-+-+
| # hops |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Multicast Address |
| |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| |
| Source Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Mtrace2 Client Address |
| | MBZ |T|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Query ID Type | Client Port # Value .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1

5.1. # hops: 8

MBZ: 7 bits
This field specifies the maximum number of hops that the mtrace2
client wants to trace. must be zeroed on transmission and ignored on
reception.

T-bit (Transitive Attribute): 1 bit
If there is some error condition in the
middle of the path that prevents an mtrace2 Reply from being received TLV type is unrecognized 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

This field specifies the 32 bits length IPv4 or 128 bits length IPv6
multicast address to be traced, or receiving router, then this
TLV is filled with "all 1" in case of
IPv4 either discarded or forwarded along with the unspecified address (::) in case Query,
depending on the value of IPv6 if no
group-specific information this bit. If this bit is set, then the
router MUST forward this TLV. If this bit is desired. Note that non-group-specific
mtrace2 clear, the router
MUST specify source address.

5.3. Source Address send an mtrace2 Reply with an UNKNOWN_QUERY error.

Extended Query Type: 16 bits
This field specifies the 32 bits length IPv4 or 128 bits length IPv6
address type of the multicast source for Extended Query Block.

Value: 16 bits
This field specifies the path being traced, or is
filled with "all 1" in case value of IPv4 or with the unspecified address
(::) in case this Extended Query.

3.2.3. Mtrace2 Request

The format of IPv6 if no source-specific information such as a
trace for RPT in PIM-SM an Mtrace2 Request message is desired. Note that non-source-specific
traceroutes may not be possible with certain multicast routing
protocols.

5.4. similar to an Mtrace2 Client Address

This
Query except the Type field specifies is 0x02.

When a LHR receives an Mtrace2 Query message, it would turn the 32 bits length IPv4 or 128 bits length IPv6
global address Query
into a Request by changing the Type field of the mtrace2 client. Query from 0x01 to
0x02. The trace starts at this
client address and proceeds toward LHR would then append an Mtrace2 Standard Response Block
(see Section 3.2.5) of its own to the traffic source.

5.5. 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 ID: 16 bits

This
except the Type field is used as 0x03.

When a unique identifier for this mtrace2 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 so
that duplicate or delayed Replies may be detected.

5.6. Client Port #

Mtrace2 from 0x02 to 0x03. The Reply is sent back message would then
be unicated to the address Mtrace2 client specified in an the Mtrace2 Client
Address field. This field specifies the UDP port

There are a number the of cases an intermediate router will send Mtrace2 Reply. This client port number MUST NOT be
changed by any router.

6. 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

Each intermediate IPv4 router in a trace path appends "response data
block" to

This section describes the forwarded trace packet. message format of an IPv4 Mtrace2 Standard
Response Block. The standard response data
block looks as follows. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Incoming Interface Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outgoing Interface Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Previous-Hop Upstream Router Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Input packet count on incoming interface .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Output packet count on outgoing interface .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Total number of packets for this source-group pair .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rtg Protocol | Multicast Rtg Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Fwd TTL | MBZ |S| Src Mask |Forwarding Code|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.1.

MBZ: 8 bit

Must bits
This field must be zeroed on transmission and ignored on
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 Mtrace2 Query or Request packet at this
router. The 32-
bit 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

Note that Mtrace2 does not require synchronizing NTP timestamp among all the routers along paths on the path to
have synchronized clocks in order to measure one-way latency. The use of

Additionally, Query Arrival Time is useful to measure for measuring the packets per second (PPS).
Suppose
packet rate. For example, suppose that a client issues two queries Q1 and Q2,
queries, and the corresponding requests R1 and R2 arrive at router
X at t1 time T1 and t2, T2, then the client would be able to calculate compute the PPS at
packet rate on router X by using the packet count results at t1 information
stored in the R1 and t2.

6.3. R2, and the time T1 and T2.

Incoming Interface Address: 32 bits
This field specifies the address of the interface on which packets
from this the source and group or the RP 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 the source and group flow or the RP are expected to transmit towards the specified destination,
receiver, or 0 if unknown or unnumbered.

6.5. Previous-Hop This is also the address
of the interface on which the Mtrace2 Query or Request arrives.

Upstream Router Address: 32 bits
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) ALL-[protocol]-ROUTERS.MCAST.NET) if the previous hop
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.

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" all 1's if no
count can be reported. This counter may have the same value as
ifHCInMulticastPkts from the IF-MIB [12] [9] for this interface.

6.7.

Output packet count on outgoing interface: 64 bits 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" all 1's if no count can be reported.
This counter may have the same value as ifHCOutMulticastPkts from
the IF-
MIB IF-MIB [9] 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 the router to the specified group, or "all 1" all 1's if no
count can be reported. If the S bit is set, set (see below), the count
is for the source network, as specified by the Src Mask field. 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 [13] [10] for this
forwarding entry.

6.9.

Rtg Protocol: 16 bits
This field describes the routing protocol unicast routing protocol running between
this router and the upstream router, and it is used to decide an determine
the RPF interface for the requested source. specified source or RP. This value
should have the same value as ipMcastRouteRtProtocol from the
IPMROUTE-STD-MIB [13] [10] for this entry. If the router is not able
to obtain this value, "all 0" all 0's must be specified.

6.10.

Multicast Rtg Protocol: 16 bits
This field describes the multicast routing protocol in use between
this
the router and the previous-hop upstream router. This value should have the
same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [13] [10]
for this entry. If the router does not able to cannot obtain this value, "all
0" all 0's
must be specified.

6.11.

Fwd TTL: 8 bits
This field contains the TTL that a in which an Mtrace2 Request packet is required to have before
it will can
be forwarded over towards the outgoing interface.

6.12. source or the RP.

S: 1 bit

This S
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.

6.13.

Src Mask: 7 bits
This field contains the number of 1's in the netmask this 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).

6.14.

Forwarding Code: 8 bits
This field contains a forwarding information/error code.
Section 9.2
explains 4.1 and Section 4.2 will explain how and when the forwarding code
Forwarding Code is filled. Defined values are as follows; follows:

Value Name Description
----- -------------- ------------------------------------------- ----------------------------------------------
0x00 NO_ERROR No error
0x01 WRONG_IF Mtrace2 Request arrived on an interface
to which this router would not forward for
this source, group, destination.
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
Mtrace2 Request.
0x03 PRUNE_RCVD This router has stopped forwarding for this
source and group in response to a request
from the next hop downstream router.
0x04 SCOPED The group is subject to administrative
scoping at this hop. 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 last-hop
router. LHR.
0x07 NOT_FORWARDING This router is not forwarding this source, source and
group out the outgoing interface for an
unspecified reason.
0x08 REACHED_RP Reached the Rendezvous Point or Core 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 querier

0x81 NO_SPACE There was not enough room to insert another
response data block in the packet.

0x82 ADMIN_PROHIB
Mtrace2 is administratively prohibited.

Note that if client.
0x0D UNKNOWN_QUERY A non-transitive Extended Query Type was
received by a router discovers there is which does not enough room in a packet
to insert its response, it puts the NO_SPACE code value in the
previous router's Forwarding Code field, overwriting any error the
previous router placed there. After the router sends the Reply to
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 support
the
details.

The type.
0x80 bit of the Forwarding Code is used to indicate a fatal
error. FATAL_ERROR A fatal error is one where the router may
know the previous
hop upstream router but cannot forward
the message to it.

7. IPv6 Mtrace2
0x81 NO_SPACE There was not enough room to insert another
Standard Response Block

Each intermediate IPv6 router in a trace path appends "response data
block" to the forwarded trace packet.
0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited.

3.2.6. IPv6 Mtrace2 Standard Response Block

This section describes the message format of an IPv6 Mtrace2 Standard
Response Block. The standard response data
block looks as follows. Type field is also 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Incoming Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outgoing Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
* Local Address *
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
* Remote Address *
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Input packet count on incoming interface .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Output packet count on outgoing interface .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Total number of packets for this source-group pair .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rtg Protocol | Multicast Rtg Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ 2 |S|Src Prefix Len |Forwarding Code|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

7.1.

MBZ: 8 bit

Must bits
This field must be zeroed on transmission and ignored on
reception.

7.2.

Query Arrival Time: 32 bits
Same definition described as in Section 6.2

7.3. IPv4.

Incoming Interface ID: 32 bits
This field specifies the interface ID on which packets from this the
source and group or RP are expected to arrive, or 0 if unknown. This ID
should be the value taken from InterfaceIndex of the IF-MIB [12] [9]
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 to which packets from this the
source and group flow or RP are expected to the specified destination, transmit, or 0 if unknown. This ID
should be the value taken from InterfaceIndex of the IF-MIB [9]
for this interface. This field is carried in network byte order.

7.5. interface

Local Address Address: 128 bits
This field specifies a global IPv6 address that uniquely
identifies the router. A 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 link-
local addresses, its link-local address can be specified in this
field.

7.6.

Remote Address Address: 128 bits
This field specifies the address of the previous-hop upstream router, which, in
most cases, is a link-local unicast address for the queried source
and destination addresses. upstream
router.

Although a link-local address does not have enough information to
identify a node, it is possible to detect the previous-hop upstream router with
the assistance of Incoming Interface ID and the current router
address (i.e., Local Address).

This

Note that this may be a multicast group (e.g., ALL-[protocol]-
ROUTERS.MCAST.NET) if the previous hop upstream router is not known because of
the workings of the a multicast routing protocol. However, it should
be the unspecified address (::) if the incoming interface address
is unknown.

7.7.

Input packet count on incoming interface interface: 64 bits
Same definition described as in Section 6.6

7.8. IPv4.

Output packet count on outgoing interface interface: 64 bits
Same definition described as in Section 6.7

7.9. IPv4.

Total number of packets for this source-group pair

This field counts the number of packets from the specified source
forwarded by this router to the specified group, or "all 1" pair: 64 bits
Same definition as in IPv4, except if no
count can be reported. If the S bit is set, 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 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.

7.10.

Rtg Protocol: 16 bits
Same definition described as in Section 6.9

7.11. IPv4.

Multicast Rtg Protocol: 16 bits
Same definition described as in Section 6.10

7.12. IPv4.

MBZ 2: 15 bits
This field must be zeroed on transmission and ignored on
reception.

S: 1 bit

This S bit indicates that the packet count for the source-group pair
is for the source network,
Same definition as determined by masking the source
address with in IPv4, except the Src Prefix Len field.

7.13. field is
used to mask the source address.

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)

7.14. (0xff).

Forwarding Code: 8 bits
Same definition described as in Section 6.14

8. IPv4.

3.2.7. Mtrace2 Augmented Response Block

In addition to the standard response block, Standard Response Block, a multicast router on the
traced path will be able to can optionally add "augumented response block" when it sends one or multiple Augmented Response
Blocks before sending the mtrace2 Request to its upstream router or sends the Reply to the
Mtrace2 Client Address. This augmented response block router.

The Augmented Response Block is flexible to
add for various information. purposes such as
providing diagnosis information (see Section 7) and protocol
verification. It's Type field is 0x05, and its format is as follows:

The augmented response block is always appended to mtrace2 TLV header
(0x04). The

MBZ: 8 bits
This field must be zeroed on transmission and ignored on
reception.

Augmented Response Type: 16 bits Type filed of
This field specifies the augmented response block is
defined for type of various purposes, such responses from a
multicast router that might need to communicate back to the
Mtrace2 client as well as diagnosis (as in Section 12)
and protocol verification. The packet length of the augmented
response block is specified in multicast routers on the augmented response block TLV
header as seen in Section 4.1. traced
path.

The following augmented response block type Augmented Response Type is defined: defined as follows:

Code Type
====== =================================================
==== ===============================================
0x01 # Mtrace2 of the returned Standard Response Blocks Returned

When the NO_SPACE error occurs, occurs on a router, the router sends back the mtrace2
Reply with contained data (i.e., all appended response blocks), and
continues should send
the mtrace2 Query by sending an mtrace2 original Mtrace2 Request received from the downstream router
as will be
described in Section 9.3. a Reply back to the Mtrace2 client, and continue with a new
Mtrace2 Request. In this mtrace2 the new Request, the router
appends the augmented response block would add a
Standard Response Block followed by an Augmented Response Block
with 0x01 as the code "0x01" Augmented Response Type, and the number of the
returned mtrace2 response blocks. Every router between
this router and Mtrace2 Standard Response Blocks as the first-hop Value.

Each upstream router can would recognize the limit total number of hops the
Request has been traced so far by referring adding this number and the # hops
number of the Standard Response Block in the header. current Request
message.

This document only defines the above augmented response block type
and does not define other augmented response block types. Specifing one Augmented Response Type in the
Augmented Response Block. The description on how to deal with provide
diagnosis information using the Augmented Response Block is out of
the scope of this document, and will be also described addressed in separate
documents.

9. Router Behavior

All

Value: variable length
The format is based on the Augmented Response Type value. The
length of these actions are performed in addition to (NOT instead of)
forwarding the packet, if applicable. E.g. a multicast packet that
has TTL or value field is Length field minus 6.

4. Router Behavior

This section describes the hop limit remaining MUST be forwarded normally, as
MUST a unicast packet that has TTL or router behavior in the hop limit remaining and is
not addressed to this router.

9.1. context of Mtrace2
in details.

4.1. Receiving Mtrace2 Query

An mtrace2 Mtrace2 Query message is an mtrace2 Mtrace2 message with no response
blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 mtrace2.

9.1.1. of 0x01.

4.1.1. Query Packet Verification

Upon receiving an mtrace2 Mtrace2 Query message, a router MUST examine
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.

Mtrace2 supports non-local client to the LHR. It is up to the
implementation to filter out such queries.

In the case when it is a local client, the router must then examine
the Query to see if it is the proper last-hop router LHR for the destination address
in the packet. It is the proper last-hop router LHR if it has a multicast-capable
interface on the same subnet as the Mtrace2 Client Address and is the
router that would forward traffic from the given (S,G) or (*,G) onto
that subnet.

If the router determines that it is not the proper last-hop router, LHR, or it cannot
make that determination, it does one of two things depending if on
whether the Query was received via multicast or unicast. If the
Query was received via multicast, then it MUST be silently dropped. discarded.
If it was received via unicast, the router turns the Query into a forwarding code of WRONG_LAST_HOP
is noted
Reply message by changing the TLV type to 0x03 and processing continues 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 Section 9.2. the Mtrace2 Query.

Duplicate Query messages as identified by the tuple (Mtrace2 Client
Address, Query ID) SHOULD be ignored. This MAY be implemented using
a simple 1-back cache (i.e. remembering of previously processed queries keyed by the Mtrace2 Client
Address and Query ID pair. The duration of the previous Query message that was processed, and
ignoring future messages with the same Mtrace2 Client Address and
Query ID). cached entries is
implementation specific. Duplicate Request messages MUST NOT be
ignored in this manner.

9.1.2.

4.1.2. Query Normal Processing

When a router receives an mtrace2 Mtrace2 Query and it determines that it is
the proper last-hop router, LHR, it it changes turns the Query to a Request by changing the TLV
type from 0x01 to 0x2 and
treats it like an mtrace2 Request 0x02, and performs the steps listed in Section 9.2.

9.1.3. Mtrace2 Query Received by Non-Supported Router

When a router that does not support mtrace2 receives an mtrace2 Query
message whose destination address is multicast, the router will
silently discard the message. When the router receives an mtrace2
Query message whose destination address is the router's interface
address, the router returns an ICMP Port unreachable to the Mtrace2
Client Address.

9.2. 4.2.

4.2. Receiving Mtrace2 Request

An mtrace2 Mtrace2 Request is a traceroute an Mtrace2 message with some number of
response blocks filled in, and that uses TLV type 0x2 for IPv4 and IPv6
mtrace2.

9.2.1. of 0x02.
With the exception of the LHR, whose Request was just converted from
a Query, each Request received by a router should have at least one
Standard Response Block filled in.

4.2.1. Request Packet Verification

If the mtrace2 Mtrace2 Request does not come from an adjacent host or router,
it MUST be silently ignored. If or if
the mtrace2 Request is not addressed to this router, or if the Request is
addressed to a multicast group which is not a link-scoped group (i.e.

224/24 for IPv4, FFx2::/16 [3] [4] for IPv6), it MUST be silently
ignored. GTSM [14] [12] SHOULD be used by the router to determine whether
the host or router is adjacent or not.

9.2.2.

If the sum of the number of the Standard Response Blocks in the
received Mtrace2 Request and the value of the Augmented Response Type
of 0x01, if any, is equal or more than the # Hops in the Mtrace2
Request, it MUST be silently ignored.

4.2.2. Request Normal Processing

When a router receives an mtrace2 Request, Mtrace2 Request message, it performs the
following steps. Note that it is possible to have multiple
situations covered by the Forwarding Codes. The first one
encountered is the one that is reported, i.e. all "note forwarding code Forwarding
Code N" should be interpreted as "if forwarding code Forwarding Code is not already
set, set forwarding code Forwarding Code to N".

1. If there is room in the current buffer (or the router can
efficiently allocate more space to use), insert Prepare a new response
block into Standard Response Block to be appended to the packet
and fill in the Query Arrival Time, Outgoing Interface Address
(for IPv4 mtrace2) IPv4) or Outgoing Interface ID (for IPv6 mtrace2), IPv6), Output Packet
Count, and Fwd 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 IPv4). Note that the packet to Outgoing Interface
is the address specified in one on which the Mtrace2 Client Address field and continue the trace as described
in Section 9.3. Request message arrives.

2. Attempt to determine the forwarding information for the
specified source and group specified, group, using the same mechanisms as would
be used when a packet is received from the source destined for
the group. A state need not be instantiated, it can be a
"phantom" state created only for the purpose of the trace, such
as "dry-
run". "dry-run."

If using a shared-tree protocol and there is no source-specific
state, or if no source-specific information is desired (i.e.,
"all 1"
all 1's for IPv4 or unspecified address (::) for IPv6), group
state should be used. If there is no group state or no group-
specific information is desired, potential source state (i.e.,
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-
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
a forwarding code Forwarding Code of NO_ROUTE, sets the remaining fields that
have not yet been filled in to zero, and then forwards the
packet sends an Mtrace2
Reply back to the mtrace2 client as described in Section 9.3. Mtrace2 client.

4. Fill in the Incoming Interface Address, Previous-Hop Upstream Router Address,
Input Packet Count, Total Number of Packets, Routing Protocol,
S, and Src Mask from (or Src Prefix Len for IPv6) using the
forwarding information that
was determined. determined by the step 2.

5. If mtrace2 Mtrace2 is administratively prohibited, note the appropriate
forwarding code (ADMIN_PROHIB). Forwarding
Code of ADMIN_PROHIB. If mtrace2 Mtrace2 is administratively prohibited
and any of the fields as filled in the step 4 are considered
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 Outgoing interface is not enabled for multicast, note
forwarding code
Forwarding Code of NO_MULTICAST. If the reception Outgoing interface is
the interface from which the router would expect data to arrive
from the source, note forwarding code RPF_IF. Otherwise, if If the
reception Outgoing
interface is not one to which the router would forward data from
the source or RP to the group, a forwarding Forwarding code of WRONG_IF is
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
Outgoing or Incoming interfaces, a forwarding code Forwarding Code of SCOPED is
noted.

8. If this router is the Rendezvous Point or Core RP for the group, note a
forwarding code Forwarding Code
of REACHED_RP is noted. 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
source and group in the mtrace2 Mtrace2 Request, it notes forwarding
code Forwarding
Code of PRUNE_SENT. If the router has stopped forwarding
downstream in response to a prune sent by the next hop downstream router,
it notes forwarding code Forwarding Code of PRUNE_RCVD. If the router should
normally forward traffic downstream for this source and group downstream
but is not, it notes forwarding code Forwarding Code of NOT_FORWARDING.

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
notes forwarding code REACHED_GW.

11. The Mtrace2 client, it
notes Forwarding Code of REACHED_GW. The router continues the
processing as described in Section 4.5.

11. If the total number of the Standard Response Blocks, including
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 sent on forwarded to the previous hop or the Mtrace2
Client Address upstream router as described
in Section 9.3.

9.2.3. Mtrace2 Request Received by Non-Supported Router

When a router that does not understand mtrace2 Request messages
receives an mtrace2 Request message whose destination address is
multicast, 4.3; otherwise, the router will silently discard the message. When the
router receives an mtrace2 Request message whose destination address packet is the router's interface address, the router returns sent as an ICMP Port
unreachable Mtrace2
Reply to the Mtrace2 Client Address, and the mtrace2 client may
then issue another mtrace2 Query with the lower number of # hops.

9.3. as described in Section 4.4.

4.3. Forwarding Mtrace2 Request

9.3.1.

This section describes how an Mtrace2 Request should be forwarded.

4.3.1. Destination Address

If the Previous-hop upstream router for the mtrace2 Mtrace2 Request is known for this
request and the number of response blocks is less than the number
requested (i.e., the "# hops" field in the mtrace2 Query header),
request, the
packet Mtrace2 Request is sent to that router. If the Incoming Interface
interface is known but the Previous-hop upstream router is not known, not, the packet Mtrace2
Request is sent to an appropriate multicast address on the Incoming Interface.
interface. The
appropriate multicast address may 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, and IPv6. It MAY also be ALL-ROUTERS.MCAST.NET 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. multicast address.

4.3.2. Source Address

An mtrace2 Mtrace2 Request should be sent with the address of the router's
reception Incoming
interface. However, if the router's Incoming interface address is unnumbered, the
router can use one of its numbered interface address as the source
address.

When

4.3.3. Appending Standard Response Block

An Mtrace2 Request MUST be sent upstream towards the source or the RP
after appending a Standard Response Block to the end of the received
Mtrace2 Request. The Standard Response Block includes the multicast
states and statistics information of the router described in
Section 3.2.5.

If appending the Standard Response Block would make the Mtrace2
Request packet longer than the MTU of the Incoming Interface, or, in
the case of IPv6, longer than 1280 bytes, the router MUST change the
Forwarding Code in the REACHED_GW code is noted, last Standard Response Block of the received
Mtrace2 Request into NO_SPACE. The router then turns the Request
into a Reply, and sends back the mtrace2 Reply as described in Section 9.4. In addition to that, it must 4.4.

The router will continue the
mtrace2 Query with a new Request by proxying the original querier as in Section 9.5.

When copying from the NO_SPACE error occurs, old
Request excluding all the router sends back response blocks, followed by the mtrace2
Reply previously
prepared Standard Response Block, and an Augmented Response Block
with contained data Augmented Response Type of 0x01 and the NO_SPACE error code number of the returned
Standard Response Blocks as in
Section 9.4, and continues the mtrace2 Query by sending an mtrace2 value. The new Request containing is then
forwarded upstream.

4.4. Sending Mtrace2 Reply

An Mtrace2 Reply MUST be returned to the same mtrace2 Query header and its standard and
augmented response blocks. client by a router if the
total number of the traced routers is equal to the # Hops in the
Request. The corresponding augmented response
block type total number of the traced routers is "# Mtrace2 the sum of the
Standard Response Blocks Returned" described in
Section 8.

9.4. Sending Mtrace2 Reply

9.4.1. the Request (including the one just
added) and the number of the returned blocks, if any.

4.4.1. Destination Address

An mtrace2 Mtrace2 Reply must MUST be sent to the address specified in the Mtrace2
Client Address field in the mtrace2 Query header.

9.4.2. Mtrace2 Request.

4.4.2. Source Address

An mtrace2 Mtrace2 Reply should SHOULD be sent with the address of the router's
reception
Outgoing interface. However, if the router's Outgoing interface address is
unnumbered, the router can use one of its numbered interface address
as the source address.

9.5.

4.4.3. Appending Standard Response Block

An Mtrace2 Reply MUST be sent with the prepared Standard Response
Block appended at the end of the received Mtrace2 Request except in
the case of NO_SPACE forwarding code.

4.5. Proxying Mtrace2 Query

When a gateway (e.g., a NAT or firewall) that firewall), which needs to block
unicast packets to the mtrace2 querier Mtrace2 client, or hide information between
the gateway and the mtrace2 querier receives mtrace2 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 from an
adjacent host or mtrace2 Request from an adjacent router, it as a Reply, and sends
back the mtrace2 Reply with contained data and the REACHED_GW code back to
the address specified in the Mtrace2 Client Address field in the
mtrace2 Query header. client.

At the same time, the gateway prepares originates a new mtrace2 Mtrace2 Query message.
The gateway uses message
by copying the original mtrace2 Query Mtrace2 header as (the Query or Request without
any of the base for response blocks), and makes the new mtrace2 Query; it changes as follows:

o sets the Mtrace2 Client Address to its
Incoming Interface RPF interface's address and as the Mtrace2 Client Port # to Address;

o uses its own port
(which may be the same as the mtrace2 port number as the gateway is
listening on that port), and Client Port #; and,

o decreases # hops according to Hops by the number of standard response blocks in the Standard Response Block that
was just returned mtrace2 Reply from the
gateway. as a Reply.

The mtrace2 new Mtrace2 Query message is then sent to the previous-hop upstream router or
to an appropriate multicast address on the Incoming
Interface. RPF interface.

When the gateway receives the mtrace2 an Mtrace2 Reply from whose Query ID matches the first-hop router
or any intermediate router,
one in the original Mtrace2 header, it MUST forward relay the mtrace2 Mtrace2 Reply
back to the mtrace2 querier Mtrace2 client by replacing the Reply's header with the
original mtrace2 Query Mtrace2 header.

9.6. 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
from mtrace2 the Mtrace2 Requests. The Forwarding Code of INFO_HIDDEN forwarding code may be
used to note that, for that. For example, the incoming interface address and
packet count are for the entrance to on the domain ingress router of a domain, and the outgoing
interface address and packet count are on the exit from egress router of the domain by specifying
"all 1". The
can be specified as all 1's. Additionally, the source-group packet
count (Section 6.8 (see Section 3.2.5 and Section 7.9)
is from router, but 3.2.6) within the domain may be "all 1"
all 1's if it is hidden.

10.

5. Client Behavior

10.1.

This section describes the behavior of an Mtrace2 client in details.

5.1. Sending Mtrace2 Query

10.1.1.

An Mtrace2 client initiates an Mtrace2 Query by sending the Query to
the LHR of interest.

5.1.1. Destination 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 can be sent 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 last-hop router LHR 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 5.4 on determining the last-hop router.

10.1.2. LHR.

5.1.2. Source Address

An mtrace2 Mtrace2 Query must MUST be sent with the address of the mtrace2
querier's reception interface, client's interface address,
which would be the Mtrace2 Client Address.

10.2.

5.2. Determining the Path

The

An Mtrace2 client could send a small number of an initial query Query messages with a large "# hops" field, #
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" # 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 non-responding hop,
in the hopes that further hops may respond. These attempts should
continue until a user-defined the [Mtrace Reply Timeout] timeout has occurred.

See also Section 10.6 5.6 on receiving the results of a trace.

10.3.

5.3. Collecting Statistics

After a client has determined that it has traced the whole path or as
much as it can expect to (see Section 10.7), 5.8), it might collect
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
as described in Section 12.3 7.3 and Section 12.4.

10.4. 7.4.

5.4. Last Hop Router (LHR)

The mtrace2 querier Mtrace2 client may not know which is the last-hop router, or that
router may be behind a firewall that blocks unicast packets but
passes multicast packets. In these cases, the mtrace2 Mtrace2 Request should
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
last-hop router SHOULD ignore any mtrace2 Mtrace2 Request received via
multicast.

10.5.

5.5. First Hop Router (FHR)

The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default
multicast group for old IPv4 mtrace (v1) responses, in order to
support mtrace queriers clients that are not unicast reachable from the
first-hop first-
hop router. However, mtrace2 Mtrace2, however, does not reserve require any IPv4/IPv6
multicast addresses for mtrace2 the Mtrace2 Replies. Every mtrace2 Mtrace2 Reply is
sent to the unicast address specified in unicast address specified in the Mtrace2 Client Address
field of the Mtrace2 Reply.

5.6. Broken Intermediate Router

A broken intermediate router might simply not understand Mtrace2
packets, and drop them. The Mtrace2 client will get no Reply at all
as a result. It should then perform a hop-by-hop search by setting
the # Hops field until it gets an Mtrace2 Reply. The client may use
linear or binary search; however, the latter is likely to be slower
because a failure requires waiting for the [Mtrace Reply Timeout]
period.

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 Address field
of client needs to terminate
the mtrace2 Query header.

10.6. Broken Intermediate Router

A broken intermediate router might simply not understand mtrace2
packets, and drop them. The querier would then get no trace when the [Mtrace Reply at all
from its mtrace2 Requests. It should Timeout] timeout has occurred, and
may then perform issue another Query with a hop-by-hop
search by setting the lower number of hops field until it gets a Reply
(both linear and binary search are options, but binary is likely to
be slower because a failure requires waiting for a timeout).

10.7. # Hops.

5.8. Mtrace2 Termination

When performing an expanding hop-by-hop trace, it is necessary to
determine when to stop expanding.

10.7.1.

5.8.1. Arriving at source Source

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
the Previous-hop router Upstream Router is zero.

10.7.2.

5.8.2. Fatal error Error

A trace has encountered a fatal error if the last Forwarding Error in
the trace has the 0x80 bit set.

10.7.3.

5.8.3. No previous hop Upstream Router

A trace can not continue if the last Previous-hop Upstream Router in the trace is
set to 0.

10.7.4. Traceroute shorter than requested

5.8.4. Reply Timeout

This document defines the trace that is returned [Mtrace Reply Timeout] value, which is shorter than requested (i.e. the
number of response blocks used
to time out an Mtrace2 Reply as seen in Section 4.5, Section 5.2, and
Section 5.7. The default [Mtrace Reply Timeout] value is smaller than the "# hops" field), 10
(seconds), and can be manually changed on the
trace encountered an error Mtrace2 client and could not continue.

10.8.
routers.

5.9. Continuing after an error Error

When the NO_SPACE error occurs, as described in Section 9.3, the
multicast routers sends 4.2, a router
will send back the mtrace2 an Mtrace2 Reply to the address
specified in the Mtrace2 Client Address field in the mtrace2 Query
header. client, and continue
with a new Request (see Section 4.3.3). In this which case, the mtrace2 Mtrace2
client may receive multiple
mtrace2 Mtrace2 Replies from different routers (along
along the path). After path. When this happens, the client receives multiple mtrace2 Reply messages, it integrates (i.e.
constructs) MUST treat them as a
single mtrace2 Mtrace2 Reply message.

If a trace times out, it is very likely to be because that a router in the middle
of the path does not support mtrace2. Mtrace2. That router's address will be
in the Previous-hop router Upstream Router field of the last entry Standard Response Block in
the last response packet received. received Reply. A client may be able to determine (via
mrinfo or SNMP [11][13]) [11][10]) a list of neighbors of the non-
responding non-responding
router. If desired, each of those neighbors could be probed to
determine the remainder of the path. Unfortunately, this heuristic
may end up with multiple paths, since there is no way of knowing what
the non-responding router's algorithm for choosing a
previous-hop an upstream router
is. However, if all paths but one flow back towards the non-responding non-
responding router, it is possible to be sure that this is the correct
path.

11.

6. Protocol-Specific Considerations

11.1.

This section describes the Mtrace2 behavior with the present of
different multicast protocols.

6.1. PIM-SM

When an mtrace2 Mtrace2 reaches a PIM-SM RP RP, and the RP does not forward the
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
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
to the traffic source, and the trace group to 0. This trace Mtrace2 Query
may be unicasted to the RP.

11.2.

6.2. Bi-Directional PIM

Bi-directional PIM [7] [5] is a variant of PIM-SM that builds bi-
directional shared trees connecting multicast sources and receivers.
Along the bi-directional shared trees, multicast data is natively
forwarded from the sources to the RPA (Rendezvous Rendezvous Point Address) Link (RPL), and
from
the RPA which, to receivers without requiring source-specific state. In
contrast to PIM-SM, RP Bi-directional PIM always has the state to trace.

A Designated Forwarder (DF) for a given RPA Rendezvous Point Address
(RPA) is in charge of forwarding downstream traffic onto its link,
and forwarding upstream traffic from its link towards the RPL (Rendezvous Point Link) that
the RPA belongs to. Hence mtrace2 Mtrace2 Reply reports DF addresses or RPA
along the path.

11.3.

6.3. PIM-DM

Routers running PIM Dense Mode [15] [13] do not know the path packets
would take unless traffic is flowing. Without some extra protocol
mechanism, this means that in an environment with multiple possible
paths with branch points on shared media, mtrace2 Mtrace2 can only trace
existing paths, not potential paths. When there are multiple
possible paths but the branch points are not on shared media, the
previous hop
upstream router is known, but the last-hop router LHR may not know that it is the
appropriate last hop.

When traffic is flowing, PIM Dense Mode routers know whether or not
they are the last-hop forwarder LHR for the link (because they won or lost an Assert
battle) and know who the previous hop upstream router is (because it won an Assert
battle). Therefore, mtrace2 Mtrace2 is always able to follow the proper path
when traffic is flowing.

11.4.

6.4. IGMP/MLD Proxy

When an mtrace2 IGMP/MLD Proxy [6] receives an Mtrace2 Query packet reaches on an
incoming interface of IGMP/
MLD Proxy [8], interface, it puts notes a WRONG_IF (0x01) value in the Forwarding Code of
mtrace2 standard response block (as in the
last Standard Response Block (see Section 6.14) 3.2.5), and sends the
mtrace2
Mtrace2 Reply back to the Mtrace2 Client Address. When client. On the other hand, when an mtrace2
Mtrace2 Query packet reaches an outgoing interface of the IGMP/MLD
proxy, it is forwarded through onto its incoming interface towards the
upstream router.

11.5. AMT

AMT [9] provides the multicast connectivity to the unicast-only
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

7. Problem Diagnosis

This section describes different scenarios Mtrace2 can be used to
diagnose the
appropriate multicast router.

12. Problem Diagnosis

12.1. problems.

7.1. Forwarding Inconsistencies

The forwarding error Forwarding Error code can tell if a group is unexpectedly pruned
or administratively scoped.

12.2.

7.2. TTL or Hop Limit Problems

By taking the maximum of hops (from from the source + and forwarding TTL (or hop
limit) threshold)
threshold over all hops, it is possible to discover the TTL or hop
limit required for the source to reach the destination.

12.3.

7.3. Packet Loss

By taking two traces, it is possible to find packet loss information
by comparing the difference in input packet counts to the difference
in output packet counts for the specified source-group address pair
at the previous hop. On a point-to-point link, any difference in
these numbers implies packet loss. Since the packet counts may be
changing as the mtrace2 Query Mtrace2 Request is propagating, there may be small
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
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
to other routers or hosts on the link injecting packets. This
appears as "negative loss" which may mask real packet loss.

In addition to the counts of input and output packets for all
multicast traffic on the interfaces, the response data Standard Response Block
includes a count of the packets forwarded by a node for the specified source-
group
source-group pair. Taking the difference in this count between two
traces and then comparing those differences between two hops gives a
measure of packet loss just for traffic from the specified source to
the specified receiver via the specified group. This measure is not
affected by shared links.

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
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 at the next hop. The counters in the response data Standard Response Block
do not allow these cases to be distinguished. Differences in packet
counts between the incoming and outgoing interfaces on one node
cannot generally be used to measure queue overflow in the node.

12.4.

7.4. Link Utilization

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
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
estimated to see whether packet loss may be due to the rate limit or
the physical capacity on a particular link being exceeded.

12.5.

7.5. Time Delay

If the routers have synchronized clocks, it is possible to estimate
propagation and queuing delay from the differences between the
timestamps at successive hops. However, this delay includes control
processing overhead, so is not necessarily indicative of the delay
that data traffic would experience.

13.

8. IANA Considerations

The following new assignments can only be made via a Standards Action
as specified in [4].

13.1. [7].

8.1. Forwarding Codes

New Forwarding codes Codes must only be created by an RFC that modifies
this document's Section 10, 3.2.5 and Section 3.2.6, fully describing the
conditions under which the new forwarding code Forwarding Code is used. The IANA may
act as a central repository so that there is a single place to look
up forwarding
codes Forwarding Codes and the document in which they are defined.

13.2.

8.2. UDP Destination Port and IPv6 Address

The IANA should allocate UDP destination port for multicast
traceroute version 2 Mtrace2 upon
publication of the first RFC.

14.

9. Security Considerations

14.1.

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
network topology is a secret, mtrace2 Mtrace2 may be restricted at the border
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
groups and at what rates. If this information is a secret, mtrace2 Mtrace2
may be restricted at the border of your domain, using the
ADMIN_PROHIB forwarding code.

14.3.

9.4. Limiting Query/Request Rates

Routers should

A router may limit mtrace2 Mtrace2 Queries and Requests by ignoring some of
the
received consecutive messages. Routers The router MAY randomly ignore the
received messages to minimize the processing overhead, i.e., to keep
fairness in processing queries. queries, or prevent traffic amplification.
The rate limit is left to the router's implementation.

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.

15.

10. Acknowledgements

This specification started largely as a transcription of Van
Jacobson's slides from the 30th IETF, and the implementation in
mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve
Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original
multicast traceroute client, mtrace (version 1), has been implemented
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
Pusateri.

For the mtrace Mtrace version 2 specification, the authors would like to
give special thanks to Tatsuya Jinmei, Bill Fenner, and Steve Casner.
Also, extensive comments were received from David L. Black, Ronald
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.

11. References

16.1.

11.1. Normative References

[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.

[2]

[3] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.

[3]

[4] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.

[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 4291, February 2006.

[7]

[5] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-PIM)",
RFC 5015, October 2007.

[8]

[6] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet
Group Management Protocol (IGMP) / Multicast Listener Discovery
(MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")",
RFC 4605, August 2006.

[9] Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and

[7] Narten, T.
Pusateri, "Automatic IP Multicast Without Explicit Tunnels
(AMT)", draft-ietf-mboned-auto-multicast-08.txt (work and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in
progress), October 2007.

16.2. RFCs", RFC 5226, May 2008.

11.2. Informative References

[10]

[8] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version 3",
RFC 3376, October 2002.

[11] Draves, R. and D. Thaler, "Default Router Preferences and More-
Specific Routes", RFC 4191, November 2005.

[12]

[9] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB",
RFC 2863, June 2000.

[13]

[10] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB",
RFC 5132, December 2007.

[14]

[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,
October 2007.

[15]

[13] Adams, A., Nicholas, J., and W. Siadak, "Protocol Independent
Multicast - Dense Mode (PIM-DM): Protocol Specification
(Revised)", RFC 3973, January 2005.

Authors' Addresses

Hitoshi Asaeda
Keio University
Graduate School of Media and Governance
Fujisawa, Kanagawa 252-0882
National Institute of Information and Communications Technology
4-2-1 Nukui-Kitamachi
Koganei, Tokyo 184-8795
Japan

Email: asaeda@wide.ad.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
Packet Design, asaeda@nict.go.jp

WeeSan Lee (editor)
Juniper Networks, Inc.
Palo Alto,
1194 North Mathilda Avenue
Sunnyvale, CA 94304 94089-1206
US

Email: casner@packetdesign.com weesan@juniper.net