--- 1/draft-ietf-mboned-mtrace-v2-09.txt 2013-07-09 00:14:22.287380440 -0700 +++ 2/draft-ietf-mboned-mtrace-v2-10.txt 2013-07-09 00:14:22.359382253 -0700 @@ -1,152 +1,152 @@ MBONED Working Group H. Asaeda Internet-Draft NICT Intended status: Standards Track W. Lee, Ed. -Expires: April 25, 2013 Juniper Networks, Inc. - October 22, 2012 +Expires: January 10, 2014 Juniper Networks, Inc. + July 09, 2013 Mtrace Version 2: Traceroute Facility for IP Multicast - draft-ietf-mboned-mtrace-v2-09 + draft-ietf-mboned-mtrace-v2-10 Abstract This document describes the IP multicast traceroute facility, named Mtrace version 2 (Mtrace2). Unlike unicast traceroute, Mtrace2 requires special implementations on the part of routers. This specification describes the required functionality in multicast routers, as well as how an Mtrace2 client invokes a query and receives a reply. -Status of this Memo +Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on April 25, 2013. + This Internet-Draft will expire on January 10, 2014. Copyright Notice - Copyright (c) 2012 IETF Trust and the persons identified as the + Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents - 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 - 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 6 - 3. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 7 - 3.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 8 - 3.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 8 - 3.2.1. Mtrace2 Query . . . . . . . . . . . . . . . . . . . . 9 - 3.2.2. Mtrace2 Extended Query Block . . . . . . . . . . . . . 10 - 3.2.3. Mtrace2 Request . . . . . . . . . . . . . . . . . . . 11 - 3.2.4. Mtrace2 Reply . . . . . . . . . . . . . . . . . . . . 11 - 3.2.5. IPv4 Mtrace2 Standard Response Block . . . . . . . . . 12 - 3.2.6. IPv6 Mtrace2 Standard Response Block . . . . . . . . . 16 - 3.2.7. Mtrace2 Augmented Response Block . . . . . . . . . . . 19 - 4. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 20 - 4.1. Receiving Mtrace2 Query . . . . . . . . . . . . . . . . . 20 - 4.1.1. Query Packet Verification . . . . . . . . . . . . . . 20 - 4.1.2. Query Normal Processing . . . . . . . . . . . . . . . 21 - 4.2. Receiving Mtrace2 Request . . . . . . . . . . . . . . . . 21 - 4.2.1. Request Packet Verification . . . . . . . . . . . . . 21 - 4.2.2. Request Normal Processing . . . . . . . . . . . . . . 22 - 4.3. Forwarding Mtrace2 Request . . . . . . . . . . . . . . . . 23 - 4.3.1. Destination Address . . . . . . . . . . . . . . . . . 24 - 4.3.2. Source Address . . . . . . . . . . . . . . . . . . . . 24 - 4.3.3. Appending Standard Response Block . . . . . . . . . . 24 - 4.4. Sending Mtrace2 Reply . . . . . . . . . . . . . . . . . . 24 - 4.4.1. Destination Address . . . . . . . . . . . . . . . . . 25 - 4.4.2. Source Address . . . . . . . . . . . . . . . . . . . . 25 - 4.4.3. Appending Standard Response Block . . . . . . . . . . 25 - 4.5. Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . . 25 - 4.6. Hiding Information . . . . . . . . . . . . . . . . . . . . 26 - 5. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 26 - 5.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 26 - 5.1.1. Destination Address . . . . . . . . . . . . . . . . . 26 - 5.1.2. Source Address . . . . . . . . . . . . . . . . . . . . 26 - 5.2. Determining the Path . . . . . . . . . . . . . . . . . . . 26 - 5.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 27 - 5.4. Last Hop Router (LHR) . . . . . . . . . . . . . . . . . . 27 - 5.5. First Hop Router (FHR) . . . . . . . . . . . . . . . . . . 27 - 5.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 27 - 5.7. Non-Supported Router . . . . . . . . . . . . . . . . . . . 28 - 5.8. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 28 - 5.8.1. Arriving at Source . . . . . . . . . . . . . . . . . . 28 - 5.8.2. Fatal Error . . . . . . . . . . . . . . . . . . . . . 28 - 5.8.3. No Upstream Router . . . . . . . . . . . . . . . . . . 28 - 5.8.4. Reply Timeout . . . . . . . . . . . . . . . . . . . . 28 - 5.9. Continuing after an Error . . . . . . . . . . . . . . . . 28 - 6. Protocol-Specific Considerations . . . . . . . . . . . . . . . 29 - 6.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 29 - 6.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 29 - 6.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 30 - 6.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 30 - 7. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 30 - 7.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 30 - 7.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 30 - 7.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 30 - 7.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 31 - 7.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 31 - 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 - 8.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 32 - 8.2. UDP Destination Port . . . . . . . . . . . . . . . . . . . 32 - 9. Security Considerations . . . . . . . . . . . . . . . . . . . 32 - 9.1. Addresses in Mtrace2 Header . . . . . . . . . . . . . . . 32 - 9.2. Topology Discovery . . . . . . . . . . . . . . . . . . . . 32 - 9.3. Characteristics of Multicast Channel . . . . . . . . . . . 32 - 9.4. Limiting Query/Request Rates . . . . . . . . . . . . . . . 33 - 9.5. Limiting Reply Rates . . . . . . . . . . . . . . . . . . . 33 - 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33 - 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33 - 11.1. Normative References . . . . . . . . . . . . . . . . . . . 33 - 11.2. Informative References . . . . . . . . . . . . . . . . . . 34 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34 + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 + 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5 + 3. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 6 + 3.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . 7 + 3.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . 7 + 3.2.1. Mtrace2 Query . . . . . . . . . . . . . . . . . . . . 8 + 3.2.2. Mtrace2 Request . . . . . . . . . . . . . . . . . . . 10 + 3.2.3. Mtrace2 Reply . . . . . . . . . . . . . . . . . . . . 10 + 3.2.4. IPv4 Mtrace2 Standard Response Block . . . . . . . . 10 + 3.2.5. IPv6 Mtrace2 Standard Response Block . . . . . . . . 14 + 3.2.6. Mtrace2 Augmented Response Block . . . . . . . . . . 17 + 3.2.7. Mtrace2 Extended Query Block . . . . . . . . . . . . 18 + 4. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 19 + 4.1. Receiving Mtrace2 Query . . . . . . . . . . . . . . . . . 19 + 4.1.1. Query Packet Verification . . . . . . . . . . . . . . 19 + 4.1.2. Query Normal Processing . . . . . . . . . . . . . . . 20 + 4.2. Receiving Mtrace2 Request . . . . . . . . . . . . . . . . 20 + 4.2.1. Request Packet Verification . . . . . . . . . . . . . 20 + 4.2.2. Request Normal Processing . . . . . . . . . . . . . . 20 + 4.3. Forwarding Mtrace2 Request . . . . . . . . . . . . . . . 22 + 4.3.1. Destination Address . . . . . . . . . . . . . . . . . 22 + 4.3.2. Source Address . . . . . . . . . . . . . . . . . . . 22 + 4.3.3. Appending Standard Response Block . . . . . . . . . . 23 + 4.4. Sending Mtrace2 Reply . . . . . . . . . . . . . . . . . . 23 + 4.4.1. Destination Address . . . . . . . . . . . . . . . . . 23 + 4.4.2. Source Address . . . . . . . . . . . . . . . . . . . 23 + 4.4.3. Appending Standard Response Block . . . . . . . . . . 23 + 4.5. Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . 24 + 4.6. Hiding Information . . . . . . . . . . . . . . . . . . . 24 + 5. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 25 + 5.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 25 + 5.1.1. Destination Address . . . . . . . . . . . . . . . . . 25 + 5.1.2. Source Address . . . . . . . . . . . . . . . . . . . 25 + 5.2. Determining the Path . . . . . . . . . . . . . . . . . . 25 + 5.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 25 + 5.4. Last Hop Router (LHR) . . . . . . . . . . . . . . . . . . 25 + 5.5. First Hop Router (FHR) . . . . . . . . . . . . . . . . . 26 + 5.6. Broken Intermediate Router . . . . . . . . . . . . . . . 26 + 5.7. Non-Supported Router . . . . . . . . . . . . . . . . . . 26 + 5.8. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 27 + 5.8.1. Arriving at Source . . . . . . . . . . . . . . . . . 27 + 5.8.2. Fatal Error . . . . . . . . . . . . . . . . . . . . . 27 + 5.8.3. No Upstream Router . . . . . . . . . . . . . . . . . 27 + 5.8.4. Reply Timeout . . . . . . . . . . . . . . . . . . . . 27 + 5.9. Continuing after an Error . . . . . . . . . . . . . . . . 27 + 6. Protocol-Specific Considerations . . . . . . . . . . . . . . 28 + 6.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . 28 + 6.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . 28 + 6.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . 28 + 6.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . 29 + 7. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 29 + 7.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . 29 + 7.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 29 + 7.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 29 + 7.4. Link Utilization . . . . . . . . . . . . . . . . . . . . 30 + 7.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . 30 + 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 + 8.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . 30 + 8.2. UDP Destination Port . . . . . . . . . . . . . . . . . . 31 + 9. Security Considerations . . . . . . . . . . . . . . . . . . . 31 + 9.1. Addresses in Mtrace2 Header . . . . . . . . . . . . . . . 31 + 9.2. Topology Discovery . . . . . . . . . . . . . . . . . . . 31 + 9.3. Characteristics of Multicast Channel . . . . . . . . . . 31 + 9.4. Limiting Query/Request Rates . . . . . . . . . . . . . . 31 + 9.5. Limiting Reply Rates . . . . . . . . . . . . . . . . . . 31 + 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32 + 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 32 + 11.1. Normative References . . . . . . . . . . . . . . . . . . 32 + 11.2. Informative References . . . . . . . . . . . . . . . . . 33 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33 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 version 2 or Mtrace2 which allows the tracing of an IP multicast routing 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 + and receiver meet in PIM-SM [5]. 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 a source to a receiver. o To isolate packet loss problems (e.g., congestion). o To isolate configuration problems (e.g., TTL threshold). @@ -179,21 +179,21 @@ Figure 1 When an Mtrace2 client initiates a multicast trace anywhere on the Internet, it sends an Mtrace2 Query packet to the LHR for a multicast group and a source address. The LHR turns the Query packet into a Request, appends a standard response block containing its interface addresses and packet statistics to the Request packet, then forwards 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 + to the group if the upstream 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 Reply may be returned before reaching the FHR if it reaches the RP first, or a fatal error condition such as "no route" is encountered along the path, or the hop count is exceeded. @@ -215,26 +215,25 @@ Mtrace2 supports both IPv4 and IPv6. Unlike the previous version of 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 In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", - and "OPTIONAL" are to be interpreted as described in RFC 2119 [2], + and "OPTIONAL" are to be interpreted as described in RFC 2119 [1], and indicate requirement levels for compliant Mtrace2 implementations. 2.1. Definitions - Since 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 The interface on which data is expected to arrive from the specified source and group. Outgoing interface The interface to which data from the source or RP is expected to @@ -249,88 +248,87 @@ First-hop router (FHR) The router that is directly connected to the source the Mtrace2 Query specifies. Last-hop router (LHR) The router that is directly connected to the receivers. It is also the router that receives the Mtrace2 Query from an Mtrace2 client. Group state - It is the state a shared-tree protocol, such as PIM-SM [1], uses + It is the state a shared-tree protocol, such as PIM-SM [5], uses to choose the upstream router towards the RP for the specified group. In this state, source-specific state is not available for the corresponding group address on the router. Source-specific state It is the state that is used to choose the path towards the source for the specified source and group. ALL-[protocol]-ROUTERS.MCAST.NET It is a link-local multicast address for multicast routers to communicate with their adjacent routers that are running the same routing protocol. For instance, the address of ALL-PIM- - ROUTERS.MCAST.NET [1] is '224.0.0.13' for IPv4 and 'ff02::d' for + ROUTERS.MCAST.NET [5] is '224.0.0.13' for IPv4 and 'ff02::d' for IPv6. 3. Packet Formats This section describes the details of the 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 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. All Mtrace2 messages are UDP packets. For IPv4, Mtrace2 Query and Request messages MUST NOT be fragmented. For IPv6, the packet size for the Mtrace2 messages MUST NOT exceed 1280 bytes, which is the - smallest MTU for an IPv6 interface [3]. The source port is uniquely + smallest MTU for an IPv6 interface [2]. The source port is uniquely selected by the local host operating system. The destination port is the IANA reserved Mtrace2 port number (see Section 8). All Mtrace2 messages MUST have a valid UDP checksum. Additionally, Mtrace2 supports both IPv4 and IPv6, but not mixed. - For example, if an Mtrace2 Query or Reply message arrives in as an + For example, if an Mtrace2 Query or Request message arrives in as an IPv4 packet, all addresses specified in the 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 format of the Value field. For all the 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 entired Mtrace2 packet length should not - exceeed the available MTU. + defined; however the entire Mtrace2 packet length should not + exceed the available MTU. Value: variable length 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 field MUST be transmitted as 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 @@ -330,33 +328,33 @@ ==== ================================ 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 Reply TLV. The first TLV determines the type of each Mtrace2 message. - 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 + Following a Query TLV, there can be a sequence of optional Extended + Query Blocks. In the case of a Request or a Reply TLV, 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. We will describe each message type in details in the next few sections. 3.2.1. Mtrace2 Query - An Mtrace2 query is usually originated by an Mtrace2 client which + An Mtrace2 Query is usually originated by an Mtrace2 client which sends an Mtrace2 Query message to the LHR. When tracing towards the source or the RP, the intermediate routers MUST NOT modify the Query 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 | @@ -376,22 +374,21 @@ | Query ID | Client Port # | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2 # 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. + Query with the lower number of hops until it receives a Reply. Multicast Address: 32 bits or 128 bits This field specifies an IPv4 or IPv6 address, which can be either: m-1: a multicast group address to be traced; or, m-2: all 1's in case of IPv4 or the unspecified address (::) in case of IPv6 if no group-specific information is desired. Source Address: 32 bits or 128 bits @@ -414,88 +411,50 @@ Mtrace2 Reply will be sent to this address. Query ID: 16 bits This field is used as a unique identifier for this Mtrace2 Query so that duplicate or delayed Reply messages may be detected. Client Port #: 16 bits This field specifies the destination UDP port number 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 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. - - 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 - +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - | 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 +3.2.2. 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 + (see Section 3.2.4) 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 +3.2.3. 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, + Block (see Section 3.2.4) 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 + be unicasted 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 +3.2.4. 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 | @@ -570,58 +529,58 @@ 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. 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's if no count can be reported. This counter may have the same value as - ifHCInMulticastPkts from the IF-MIB [9] for this interface. + ifHCInMulticastPkts from the IF-MIB [10] for this interface. 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. + the IF-MIB [10] for this interface. Total number of packets for this source-group pair: 64 bits 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 + ipMcastRoutePkts from the IPMROUTE-STD-MIB [11] for this forwarding entry. Rtg Protocol: 16 bits 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 + IPMROUTE-STD-MIB [11] for this entry. If the router is not able to obtain this value, all 0's must be specified. Multicast Rtg Protocol: 16 bits 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] + same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [11] for this entry. If the router cannot obtain this value, all 0's must be specified. Fwd TTL: 8 bits - This field contains the TTL in which an Mtrace2 Request packet can - be forwarded towards the source or the RP. + This field contains the configured multicast TTL threshold, if + any, of the outgoing interface. S: 1 bit 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. 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, @@ -667,21 +627,21 @@ 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. -3.2.6. IPv6 Mtrace2 Standard Response Block +3.2.5. IPv6 Mtrace2 Standard Response Block This section describes the message format of an IPv6 Mtrace2 Standard Response Block. The 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 | @@ -718,66 +678,65 @@ MBZ: 8 bits This field must be zeroed on transmission and ignored on reception. Query Arrival Time: 32 bits Same definition as in IPv4. Incoming Interface ID: 32 bits This field specifies the interface ID on which packets from the source or RP are expected to arrive, or 0 if unknown. This ID - should be the value taken from InterfaceIndex of the IF-MIB [9] + should be the value taken from InterfaceIndex of the IF-MIB [10] for this interface. 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] + should be the value taken from InterfaceIndex of the IF-MIB [10] for this interface Local Address: 128 bits This field specifies a global IPv6 address that uniquely - 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. + identifies the router. An unique local unicast address [9] 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. Remote Address: 128 bits This field specifies the address of the upstream router, which, in most cases, is a link-local unicast address for the upstream router. Although a link-local address does not have enough information to identify a node, it is possible to detect the upstream router with the assistance of Incoming Interface ID and the current router address (i.e., Local Address). - 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. + 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. Input packet count on incoming interface: 64 bits Same definition as in IPv4. Output packet count on outgoing interface: 64 bits Same definition as in IPv4. 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] + the same value as ipMcastRoutePkts from the IPMROUTE-STD-MIB [11] for this forwarding entry. Rtg Protocol: 16 bits Same definition as in IPv4. Multicast Rtg Protocol: 16 bits Same definition as in IPv4. MBZ 2: 15 bits This field must be zeroed on transmission and ignored on @@ -788,29 +747,29 @@ 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). Forwarding Code: 8 bits Same definition as in IPv4. -3.2.7. Mtrace2 Augmented Response Block +3.2.6. Mtrace2 Augmented Response Block In addition to the Standard Response Block, a multicast router on the traced path can optionally add one or multiple Augmented Response Blocks before sending the Request to its upstream router. 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: + verification. Its Type field is 0x05, and its format is 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 | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Augmented Response Type | Value .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ MBZ: 8 bits @@ -845,20 +804,59 @@ 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. Value: variable length The format is based on the Augmented Response Type value. The length of the value field is Length field minus 6. +3.2.7. 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 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 separate documents. + + The Mtrace2 Extended Query Block's Type field is 0x06, and 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 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | 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. + 4. Router Behavior This section describes the router behavior in the context of Mtrace2 in details. 4.1. Receiving Mtrace2 Query An Mtrace2 Query message is an Mtrace2 message with no response blocks filled in, and uses TLV type of 0x01. @@ -909,22 +907,21 @@ An Mtrace2 Request is an Mtrace2 message that uses TLV type 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 Request does not come from an adjacent router, or if the 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 [4] for IPv6), it MUST be silently + 224/24 for IPv4, FFx2::/16 [3] 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 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 @@ -1033,21 +1030,21 @@ interface. However, if the Incoming interface is unnumbered, the router can use one of its numbered interface address as the source address. 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. + Section 3.2.4. 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 last Standard Response Block of the received Mtrace2 Request into NO_SPACE. The router then turns the Request into a Reply, and sends the Reply as described in Section 4.4. The router will continue with a new Request by copying from the old Request excluding all the response blocks, followed by the previously @@ -1115,21 +1112,21 @@ Query or Request message, and terminates the trace. 4.6. Hiding Information Information about a domain's topology and connectivity may be hidden from the Mtrace2 Requests. The Forwarding Code of INFO_HIDDEN may be used to note that. For example, the incoming interface address and packet count on the ingress router of a domain, and the outgoing interface address and packet count on the egress router of the domain can be specified as all 1's. Additionally, the source-group packet - count (see Section 3.2.5 and Section 3.2.6) within the domain may be + count (see Section 3.2.4 and Section 3.2.5) within the domain may be all 1's if it is hidden. 5. Client Behavior This section describes the behavior of an Mtrace2 client in details. 5.1. Sending Mtrace2 Query An Mtrace2 client initiates an Mtrace2 Query by sending the Query to the LHR of interest. @@ -1250,21 +1246,21 @@ will send back an Mtrace2 Reply to the Mtrace2 client, and continue with a new Request (see Section 4.3.3). In which case, the Mtrace2 client may receive multiple Mtrace2 Replies from different routers along the path. When this happens, the client MUST treat them as a single Mtrace2 Reply message. If a trace times out, it is very likely that a router in the middle of the path does not support Mtrace2. That router's address will be in the Upstream Router field of the last Standard Response Block in the last received Reply. A client may be able to determine (via - mrinfo or SNMP [11][10]) a list of neighbors of the non-responding + mrinfo or SNMP [9][11]) a list of neighbors of the 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 an upstream router is. However, if all paths but one flow back towards the non- responding router, it is possible to be sure that this is the correct path. 6. Protocol-Specific Considerations @@ -1276,21 +1272,21 @@ 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 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 Mtrace2 Query may be unicasted to the RP. 6.2. Bi-Directional PIM - Bi-directional PIM [5] is a variant of PIM-SM that builds bi- + Bi-directional PIM [6] 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 Rendezvous Point Link (RPL), and from which, to receivers without requiring source-specific state. In contrast to PIM-SM, Bi-directional PIM always has the state to trace. A Designated Forwarder (DF) for a given Rendezvous Point Address (RPA) is in charge of forwarding downstream traffic onto its link, and forwarding upstream traffic from its link towards the RPL that the RPA belongs to. Hence Mtrace2 Reply reports DF addresses or RPA @@ -1308,23 +1304,23 @@ appropriate last hop. When traffic is flowing, PIM Dense Mode routers know whether or not they are the LHR for the link (because they won or lost an Assert battle) and know who the upstream router is (because it won an Assert battle). Therefore, Mtrace2 is always able to follow the proper path when traffic is flowing. 6.4. IGMP/MLD Proxy - When an IGMP/MLD Proxy [6] receives an Mtrace2 Query packet on an + When an IGMP/MLD Proxy [7] 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 + last Standard Response Block (see Section 3.2.4), 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. 7. Problem Diagnosis This section describes different scenarios Mtrace2 can be used to diagnose the multicast problems. @@ -1385,47 +1381,47 @@ 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. 8. IANA Considerations The following new assignments can only be made via a Standards Action - as specified in [7]. + as specified in [4]. 8.1. Forwarding Codes New Forwarding Codes must only be created by an RFC that modifies - this document's Section 3.2.5 and Section 3.2.6, fully describing the + this document's Section 3.2.4 and Section 3.2.5, fully describing the conditions under which the new Forwarding Code is used. The IANA may act as a central repository so that there is a single place to look up Forwarding Codes and the document in which they are defined. 8.2. UDP Destination Port The IANA should allocate UDP destination port for Mtrace2 upon publication of the first RFC. 9. Security Considerations 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 + instance, if Mtrace2 Client Address specified in an Mtrace2 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 may be restricted at the border of your domain, using the ADMIN_PROHIB forwarding code. 9.3. Characteristics of Multicast Channel @@ -1465,67 +1461,67 @@ 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. 11. References 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. + [1] Bradner, S., "Key words for use in RFCs to indicate + requirement levels", RFC 2119, March 1997. - [3] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) - Specification", RFC 2460, December 1998. + [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 + (IPv6) Specification", RFC 2460, December 1998. - [4] Hinden, R. and S. Deering, "IP Version 6 Addressing + [3] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. - [5] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, - "Bidirectional Protocol Independent Multicast (BIDIR-PIM)", - RFC 5015, October 2007. + [4] Narten, T. and H. Alvestrand, "Guidelines for Writing an + IANA Considerations Section in RFCs", RFC 5226, May 2008. - [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. + [5] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, + "Protocol Independent Multicast - Sparse Mode (PIM-SM): + Protocol Specification (Revised)", RFC 4601, August 2006. - [7] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA - Considerations Section in RFCs", RFC 5226, May 2008. + [6] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, + "Bidirectional Protocol Independent Multicast (BIDIR- + PIM)", RFC 5015, October 2007. + + [7] 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. 11.2. Informative References [8] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. - Thyagarajan, "Internet Group Management Protocol, Version 3", - RFC 3376, October 2002. + Thyagarajan, "Internet Group Management Protocol, Version + 3", RFC 3376, October 2002. - [9] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", - RFC 2863, June 2000. + [9] Draves, R. and D. Thaler, "Default Router Preferences and + More-Specific Routes", RFC 4191, November 2005. - [10] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB", - RFC 5132, December 2007. + [10] McCloghrie, K. and F. Kastenholz, "The Interfaces Group + MIB", RFC 2863, June 2000. - [11] Draves, R. and D. Thaler, "Default Router Preferences and More- - Specific Routes", RFC 4191, November 2005. + [11] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast + MIB", RFC 5132, December 2007. - [12] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. Pignataro, - "The Generalized TTL Security Mechanism (GTSM)", RFC 5082, - October 2007. + [12] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. + Pignataro, "The Generalized TTL Security Mechanism + (GTSM)", RFC 5082, October 2007. - [13] Adams, A., Nicholas, J., and W. Siadak, "Protocol Independent - Multicast - Dense Mode (PIM-DM): Protocol Specification - (Revised)", RFC 3973, January 2005. + [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 National Institute of Information and Communications Technology 4-2-1 Nukui-Kitamachi Koganei, Tokyo 184-8795 Japan Email: asaeda@nict.go.jp