draft-ietf-mboned-mtrace-v2-01.txt   draft-ietf-mboned-mtrace-v2-02.txt 
MBONED Working Group H. Asaeda MBONED Working Group H. Asaeda
Internet-Draft Keio University Internet-Draft Keio University
Intended status: Standards Track T. Jinmei Intended status: Standards Track T. Jinmei
Expires: January 5, 2009 ISC Expires: May 7, 2009 ISC
W. Fenner W. Fenner
Arastra, Inc. Arastra, Inc.
S. Casner S. Casner
Packet Design, Inc. Packet Design, Inc.
July 4, 2008 November 3, 2008
Mtrace Version 2: Traceroute Facility for IP Multicast Mtrace Version 2: Traceroute Facility for IP Multicast
draft-ietf-mboned-mtrace-v2-01 draft-ietf-mboned-mtrace-v2-02
Status of this Memo Status of this Memo
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applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
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skipping to change at page 1, line 39 skipping to change at page 1, line 39
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Abstract Abstract
This document describes the IP multicast traceroute facility. Unlike This document describes the IP multicast traceroute facility. Unlike
unicast traceroute, multicast traceroute requires special unicast traceroute, multicast traceroute requires special
implementations on the part of routers. This specification describes implementations on the part of routers. This specification describes
the required functionality in multicast routers, as well as how the required functionality in multicast routers, as well as how
management applications can use the router functionality. management applications can use the router functionality.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 8 4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 8 4.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 8
4.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 8 4.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 8
5. Mtrace2 Header . . . . . . . . . . . . . . . . . . . . . . . . 9 5. Mtrace2 Query Header . . . . . . . . . . . . . . . . . . . . . 9
5.1. # hops: 8 bits . . . . . . . . . . . . . . . . . . . . . . 9 5.1. # hops: 8 bits . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Multicast Address . . . . . . . . . . . . . . . . . . . . 10 5.2. Multicast Address . . . . . . . . . . . . . . . . . . . . 10
5.3. Source Address . . . . . . . . . . . . . . . . . . . . . . 10 5.3. Source Address . . . . . . . . . . . . . . . . . . . . . . 10
5.4. Destination Address . . . . . . . . . . . . . . . . . . . 10 5.4. Destination Address . . . . . . . . . . . . . . . . . . . 10
5.5. Response Address . . . . . . . . . . . . . . . . . . . . . 10 5.5. Response Address . . . . . . . . . . . . . . . . . . . . . 10
5.6. Resp TTL/HopLim: 8 bits . . . . . . . . . . . . . . . . . 10 5.6. Query ID: 16 bits . . . . . . . . . . . . . . . . . . . . 10
5.7. Query ID: 24 bits . . . . . . . . . . . . . . . . . . . . 10 5.7. Client Port # . . . . . . . . . . . . . . . . . . . . . . 10
6. IPv4 Mtrace2 Response Data . . . . . . . . . . . . . . . . . . 11 6. IPv4 Mtrace2 Standard Response Block . . . . . . . . . . . . . 11
6.1. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 11 6.1. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 11
6.2. Incoming Interface Address: 32 bits . . . . . . . . . . . 12 6.2. Incoming Interface Address: 32 bits . . . . . . . . . . . 12
6.3. Outgoing Interface Address: 32 bits . . . . . . . . . . . 12 6.3. Outgoing Interface Address: 32 bits . . . . . . . . . . . 12
6.4. Previous-Hop Router Address: 32 bits . . . . . . . . . . . 12 6.4. Previous-Hop Router Address: 32 bits . . . . . . . . . . . 12
6.5. Input packet count on incoming interface: 64 bits . . . . 12 6.5. Input packet count on incoming interface: 64 bits . . . . 12
6.6. Output packet count on incoming interface: 64 bits . . . . 12 6.6. Output packet count on incoming interface: 64 bits . . . . 12
6.7. Total number of packets for this source-group pair: 64 6.7. Total number of packets for this source-group pair: 64
bits . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 bits . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.8. Rtg Protocol: 8 bits . . . . . . . . . . . . . . . . . . . 13 6.8. Rtg Protocol: 8 bits . . . . . . . . . . . . . . . . . . . 13
6.9. Fwd TTL: 8 bits . . . . . . . . . . . . . . . . . . . . . 13 6.9. Fwd TTL: 8 bits . . . . . . . . . . . . . . . . . . . . . 13
6.10. MBZ: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . 13 6.10. MBZ: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . 13
6.11. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.11. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.12. Src Mask: 6 bits . . . . . . . . . . . . . . . . . . . . . 13 6.12. Src Mask: 6 bits . . . . . . . . . . . . . . . . . . . . . 13
6.13. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 13 6.13. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 13
7. IPv6 Mtrace2 Response Data . . . . . . . . . . . . . . . . . . 16 7. IPv6 Mtrace2 Standard Response Block . . . . . . . . . . . . . 16
7.1. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 16 7.1. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 16
7.2. Incoming Interface ID: 32 bits . . . . . . . . . . . . . . 16 7.2. Incoming Interface ID: 32 bits . . . . . . . . . . . . . . 16
7.3. Outgoing Interface ID: 32 bits . . . . . . . . . . . . . . 17 7.3. Outgoing Interface ID: 32 bits . . . . . . . . . . . . . . 17
7.4. Local Address . . . . . . . . . . . . . . . . . . . . . . 17 7.4. Local Address . . . . . . . . . . . . . . . . . . . . . . 17
7.5. Remote Address . . . . . . . . . . . . . . . . . . . . . . 17 7.5. Remote Address . . . . . . . . . . . . . . . . . . . . . . 17
7.6. Input packet count on incoming interface . . . . . . . . . 17 7.6. Input packet count on incoming interface . . . . . . . . . 17
7.7. Output packet count on incoming interface . . . . . . . . 17 7.7. Output packet count on incoming interface . . . . . . . . 17
7.8. Total number of packets for this source-group pair . . . . 18 7.8. Total number of packets for this source-group pair . . . . 17
7.9. Rtg Protocol: 8 bits . . . . . . . . . . . . . . . . . . . 18 7.9. Rtg Protocol: 8 bits . . . . . . . . . . . . . . . . . . . 18
7.10. MBZ: 7 bits . . . . . . . . . . . . . . . . . . . . . . . 18 7.10. MBZ: 7 bits . . . . . . . . . . . . . . . . . . . . . . . 18
7.11. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 18 7.11. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.12. Src Prefix Len: 8 bits . . . . . . . . . . . . . . . . . . 18 7.12. Src Prefix Len: 8 bits . . . . . . . . . . . . . . . . . . 18
7.13. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 18 7.13. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 18
8. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 19 8. Mtrace2 Augmented Response Block . . . . . . . . . . . . . . . 19
8.1. Traceroute Query . . . . . . . . . . . . . . . . . . . . . 19 9. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 20
8.1.1. Packet Verification . . . . . . . . . . . . . . . . . 19 9.1. Traceroute Query . . . . . . . . . . . . . . . . . . . . . 20
8.1.2. Normal Processing . . . . . . . . . . . . . . . . . . 19 9.1.1. Packet Verification . . . . . . . . . . . . . . . . . 20
8.2. Mtrace2 Request . . . . . . . . . . . . . . . . . . . . . 19 9.1.2. Normal Processing . . . . . . . . . . . . . . . . . . 20
8.2.1. Packet Verification . . . . . . . . . . . . . . . . . 20 9.2. Mtrace2 Request . . . . . . . . . . . . . . . . . . . . . 20
8.2.2. Normal Processing . . . . . . . . . . . . . . . . . . 20 9.2.1. Packet Verification . . . . . . . . . . . . . . . . . 21
8.3. Mtrace2 Response . . . . . . . . . . . . . . . . . . . . . 21 9.2.2. Normal Processing . . . . . . . . . . . . . . . . . . 21
8.4. Forwarding Mtrace2 Requests . . . . . . . . . . . . . . . 21 9.3. Mtrace2 Response . . . . . . . . . . . . . . . . . . . . . 22
8.5. Sending Mtrace2 Responses . . . . . . . . . . . . . . . . 22 9.4. Forwarding Mtrace2 Requests . . . . . . . . . . . . . . . 22
8.5.1. Destination Address . . . . . . . . . . . . . . . . . 22 9.5. Sending Mtrace2 Responses . . . . . . . . . . . . . . . . 23
8.5.2. TTL and Hop Limit . . . . . . . . . . . . . . . . . . 22 9.5.1. Destination Address . . . . . . . . . . . . . . . . . 23
8.5.3. Source Address . . . . . . . . . . . . . . . . . . . . 22 9.5.2. TTL and Hop Limit . . . . . . . . . . . . . . . . . . 23
8.5.4. Sourcing Multicast Responses . . . . . . . . . . . . . 22 9.5.3. Source Address . . . . . . . . . . . . . . . . . . . . 23
8.6. Hiding Information . . . . . . . . . . . . . . . . . . . . 22 9.5.4. Sourcing Multicast Responses . . . . . . . . . . . . . 23
9. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 23 9.6. Hiding Information . . . . . . . . . . . . . . . . . . . . 23
9.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 23 10. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 25
9.2. Determining the Path . . . . . . . . . . . . . . . . . . . 23 10.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 25
9.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 23 10.2. Determining the Path . . . . . . . . . . . . . . . . . . . 25
9.4. Last Hop Router . . . . . . . . . . . . . . . . . . . . . 23 10.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 25
9.5. First Hop Router . . . . . . . . . . . . . . . . . . . . . 24 10.4. Last Hop Router . . . . . . . . . . . . . . . . . . . . . 26
9.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 24 10.5. First Hop Router . . . . . . . . . . . . . . . . . . . . . 26
9.7. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 24 10.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 26
9.7.1. Arriving at source . . . . . . . . . . . . . . . . . . 24 10.7. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 26
9.7.2. Fatal error . . . . . . . . . . . . . . . . . . . . . 25 10.7.1. Arriving at source . . . . . . . . . . . . . . . . . . 27
9.7.3. No previous hop . . . . . . . . . . . . . . . . . . . 25 10.7.2. Fatal error . . . . . . . . . . . . . . . . . . . . . 27
9.7.4. Traceroute shorter than requested . . . . . . . . . . 25 10.7.3. No previous hop . . . . . . . . . . . . . . . . . . . 27
9.8. Continuing after an error . . . . . . . . . . . . . . . . 25 10.7.4. Traceroute shorter than requested . . . . . . . . . . 27
10. Protocol-Specific Considerations . . . . . . . . . . . . . . . 26 10.8. Continuing after an error . . . . . . . . . . . . . . . . 27
10.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 26 11. Protocol-Specific Considerations . . . . . . . . . . . . . . . 28
10.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 26 11.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 28
10.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 26 11.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 28
10.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 26 11.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 28
10.5. AMT . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 11.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 28
11. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 28 11.5. AMT . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
11.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 28 12. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 30
11.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 28 12.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 30
11.3. Packet loss . . . . . . . . . . . . . . . . . . . . . . . 28 12.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 30
11.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 29 12.3. Packet loss . . . . . . . . . . . . . . . . . . . . . . . 30
11.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 29 12.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 31
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 12.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 31
12.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 30 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
12.2. UDP Destination Port and IPv6 Address . . . . . . . . . . 30 13.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 32
13. Security Considerations . . . . . . . . . . . . . . . . . . . 31 13.2. UDP Destination Port and IPv6 Address . . . . . . . . . . 32
13.1. Topology Discovery . . . . . . . . . . . . . . . . . . . . 31 14. Security Considerations . . . . . . . . . . . . . . . . . . . 33
13.2. Traffic Rates . . . . . . . . . . . . . . . . . . . . . . 31 14.1. Topology Discovery . . . . . . . . . . . . . . . . . . . . 33
13.3. Unicast Replies . . . . . . . . . . . . . . . . . . . . . 31 14.2. Traffic Rates . . . . . . . . . . . . . . . . . . . . . . 33
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32 14.3. Unicast Replies . . . . . . . . . . . . . . . . . . . . . 33
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33 15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 34
15.1. Normative References . . . . . . . . . . . . . . . . . . . 33 16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
15.2. Informative References . . . . . . . . . . . . . . . . . . 33 16.1. Normative References . . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35 16.2. Informative References . . . . . . . . . . . . . . . . . . 36
Intellectual Property and Copyright Statements . . . . . . . . . . 36 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37
Intellectual Property and Copyright Statements . . . . . . . . . . 38
1. Introduction 1. Introduction
The unicast "traceroute" program allows the tracing of a path from The unicast "traceroute" program allows the tracing of a path from
one machine to another. The key mechanism for unicast traceroute is one machine to another. The key mechanism for unicast traceroute is
the ICMP TTL exceeded message, which is specifically precluded as a the ICMP TTL exceeded message, which is specifically precluded as a
response to multicast packets. On the other hand, the multicast response to multicast packets. On the other hand, the multicast
traceroute facility allows the tracing of an IP multicast routing traceroute facility allows the tracing of an IP multicast routing
paths. In this document, we specify the multicast "traceroute" paths. In this document, we specify the multicast "traceroute"
facility to be implemented in multicast routers and accessed by facility to be implemented in multicast routers and accessed by
skipping to change at page 6, line 30 skipping to change at page 6, line 30
The interface on which traffic is forwarded from the specified source The interface on which traffic is forwarded from the specified source
and group toward the destination. It is the interface on which the and group toward the destination. It is the interface on which the
multicast traceroute Request was received. multicast traceroute Request was received.
Previous-hop router: Previous-hop router:
The router that is on the link attached to the Incoming Interface and The router that is on the link attached to the Incoming Interface and
is responsible for forwarding traffic for the specified source and is responsible for forwarding traffic for the specified source and
group. group.
Group state: Group state:
It is the state in which a shared-tree protocol (e.g., PIM-SM [12]) It is the state in which a shared-tree protocol (e.g., PIM-SM [9])
running on a router chooses the previous-hop router toward the core running on a router chooses the previous-hop router toward the core
router or Rendezvous Point (RP) as its parent router. In this state, router or Rendezvous Point (RP) as its parent router. In this state,
source-specific state is not available for the corresponding source-specific state is not available for the corresponding
multicast address on the router. multicast address on the router.
Source-specific state: Source-specific state:
It is the state in which a routing protocol running on a router It is the state in which a routing protocol running on a router
chooses the path that would be followed for a source-specific join. chooses the path that would be followed for a source-specific join.
ALL-[protocol]-ROUTERS.MCAST.NET: ALL-[protocol]-ROUTERS.MCAST.NET:
skipping to change at page 8, line 31 skipping to change at page 8, line 31
Length (16 bits) Length (16 bits)
Value (variable length) Value (variable length)
4.2. Defined TLVs 4.2. Defined TLVs
The following TLV Types are defined: The following TLV Types are defined:
Code Type Code Type
====== ============================ ====== ======================================
1 Mtrace2 Query 1 Mtrace2 Query
2 Mtrace2 Response 2 Mtrace2 Response
3 Mtrace2 Standard Response Block
4 Mtrace2 Augmented Response Block
The type field is defined to be "0x1" for traceroute queries and An mtrace2 message MUST contain one Mtrace2 Query or Response. An
mtrace2 message MAY contain one or multiple Mtrace2 Standard and
Augmented Responses. A multicast router that sends mtrace2 request
MUST NOT contain multiple Mtrace2 Standard blocks but MAY contain
multiple Augmented Response blocks.
The type field is defined to be "0x1" for mtrace2 queries and
requests. The type field is changed to "0x2" when the packet is requests. The type field is changed to "0x2" when the packet is
completed and sent as a response from the first hop router to the completed and sent as a response from the first hop router to the
querier. Two codes are required so that multicast routers won't querier. Two codes are required so that multicast routers will not
attempt to process a completed response in those cases where the attempt to process a completed response in those cases where the
initial query was issued from a router or the response is sent via initial query was issued from a router.
multicast.
5. Mtrace2 Header 5. Mtrace2 Query Header
The mtrace2 message is carried as a UDP packet. The UDP source port The mtrace2 message is carried as a UDP packet. The UDP source port
is uniquely selected by the local host operating system. The UDP is uniquely selected by the local host operating system. The UDP
destination port is the IANA reserved mtrace2 port number (see destination port is the IANA reserved mtrace2 port number (see
Section 12). The UDP checksum MUST be valid in mtrace2 control Section 13). The UDP checksum MUST be valid in mtrace2 messages.
messages.
The mtrace2 includes the common packet header as follows. The header The mtrace2 message includes the common mtrace2 Query header as
is only filled in by the originator of the traceroute Query; follows. The header is only filled in by the originator of the
intermediate routers MUST NOT modify any of the fields. mtrace2 Query; intermediate routers MUST NOT modify any of the
fields.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| # hops | | # hops |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Multicast Address | | Multicast Address |
| | | |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
skipping to change at page 9, line 38 skipping to change at page 9, line 38
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Destination Address | | Destination Address |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Response Address | | Response Address |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Resp TTL/HopLim| Query ID | | Query ID | Client Port # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 Figure 1
5.1. # hops: 8 bits 5.1. # hops: 8 bits
This field specifies the maximum number of hops that the requester This field specifies the maximum number of hops that the requester
wants to trace. If there is some error condition in the middle of wants to trace. If there is some error condition in the middle of
the path that keeps the traceroute request from reaching the first- the path that keeps the mtrace2 request from reaching the first-hop
hop router, this field can be used to perform an expanding-ring router, this field can be used to perform an expanding-ring search to
search to trace the path to just before the problem. trace the path to just before the problem.
5.2. Multicast Address 5.2. Multicast Address
This field specifies the 32 bits length IPv4 or 128 bits length IPv6 This field specifies the 32 bits length IPv4 or 128 bits length IPv6
multicast address to be traced, or is filled with "all 1" in case of multicast address to be traced, or is filled with "all 1" in case of
IPv4 or with the unspecified address (::) in case of IPv6 if no IPv4 or with the unspecified address (::) in case of IPv6 if no
source-specific information is desired. Note that non-group-specific group-specific information is desired. Note that non-group-specific
traceroutes may not be possible with certain multicast routing mtrace2 MUST specify source address.
protocols.
5.3. Source Address 5.3. Source Address
This field specifies the 32 bits length IPv4 or 128 bits length IPv6 This field specifies the 32 bits length IPv4 or 128 bits length IPv6
address of the multicast source for the path being traced, or is address of the multicast source for the path being traced, or is
filled with "all 1" in case of IPv4 or with the unspecified address filled with "all 1" in case of IPv4 or with the unspecified address
(::) in case of IPv6 if no source-specific information is desired. (::) in case of IPv6 if no source-specific information is desired.
Note that non-source-specific traceroutes may not be possible with Note that non-source-specific traceroutes may not be possible with
certain multicast routing protocols. certain multicast routing protocols.
5.4. Destination Address 5.4. Destination Address
This field specifies the 32 bits length IPv4 or 128 bits length IPv6 This field specifies the 32 bits length IPv4 or 128 bits length IPv6
address of the multicast receiver for the path being traced. The address of the multicast receiver for the path being traced. The
trace starts at this destination and proceeds toward the traffic trace starts at this destination and proceeds toward the traffic
source. source.
5.5. Response Address 5.5. Response Address
This field specifies 32 bits length IPv4 or 128 bits length IPv6 This field specifies 32 bits length IPv4 or 128 bits length IPv6
address to which the completed traceroute response packet gets sent. address to which the completed mtrace2 response packet gets sent. It
It can be a unicast address or a multicast address, as explained in MUST be a global unicast address as explained in Section 9.2
Section 8.2
5.6. Resp TTL/HopLim: 8 bits
This field specifies the TTL or Hop Limit at which to multicast the
response, if the response address is a multicast address.
5.7. Query ID: 24 bits 5.6. Query ID: 16 bits
This field is used as a unique identifier for this traceroute request This field is used as a unique identifier for this traceroute request
so that duplicate or delayed responses may be detected and to so that duplicate or delayed responses may be detected and to
minimize collisions when a multicast response address is used. minimize collisions when a multicast response address is used.
6. IPv4 Mtrace2 Response Data 5.7. Client Port #
Each intermediate IPv4 router in a trace path appends "response data" Mtrace2 response is sent back to the address specified in a Response
to the forwarded trace packet. The response data looks as follows. Address field. This field specifies the UDP port number the router
will send Mtrace2 Response. This client port number MUST NOT be
changed by any router.
6. IPv4 Mtrace2 Standard Response Block
Each intermediate IPv4 router in a trace path appends "response data
block" to the forwarded trace packet. The standard response data
block looks as follows.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query Arrival Time | | Query Arrival Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Incoming Interface Address | | Incoming Interface Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outgoing Interface Address | | Outgoing Interface Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 12, line 31 skipping to change at page 12, line 32
packets from this source. This may be a multicast group (e.g. ALL- packets from this source. This may be a multicast group (e.g. ALL-
[protocol]-ROUTERS.MCAST.NET) if the previous hop is not known [protocol]-ROUTERS.MCAST.NET) if the previous hop is not known
because of the workings of the multicast routing protocol. However, because of the workings of the multicast routing protocol. However,
it should be 0 if the incoming interface address is unknown. it should be 0 if the incoming interface address is unknown.
6.5. Input packet count on incoming interface: 64 bits 6.5. Input packet count on incoming interface: 64 bits
This field contains the number of multicast packets received for all This field contains the number of multicast packets received for all
groups and sources on the incoming interface, or "all 1" if no count groups and sources on the incoming interface, or "all 1" if no count
can be reported. This counter may have the same value as can be reported. This counter may have the same value as
ifHCInMulticastPkts from the IF-MIB [10] for this interface. ifHCInMulticastPkts from the IF-MIB [14] for this interface.
6.6. Output packet count on incoming interface: 64 bits 6.6. Output packet count on incoming interface: 64 bits
This field contains the number of multicast packets that have been This field contains the number of multicast packets that have been
transmitted or queued for transmission for all groups and sources on transmitted or queued for transmission for all groups and sources on
the outgoing interface, or "all 1" if no count can be reported. This the outgoing interface, or "all 1" if no count can be reported. This
counter may have the same value as ifHCOutMulticastPkts from the IF- counter may have the same value as ifHCOutMulticastPkts from the IF-
MIB for this interface. MIB for this interface.
6.7. Total number of packets for this source-group pair: 64 bits 6.7. Total number of packets for this source-group pair: 64 bits
This field counts the number of packets from the specified source This field counts the number of packets from the specified source
forwarded by this router to the specified group, or "all 1" if no forwarded by this router to the specified group, or "all 1" if no
count can be reported. If the S bit is set, the count is for the count can be reported. If the S bit is set, the count is for the
source network, as specified by the Src Mask field. If the S bit is source network, as specified by the Src Mask field. If the S bit is
set and the Src Mask field is 63, indicating no source-specific set and the Src Mask field is 63, indicating no source-specific
state, the count is for all sources sending to this group. This state, the count is for all sources sending to this group. This
counter should have the same value as ipMcastRoutePkts from the counter should have the same value as ipMcastRoutePkts from the
IPMROUTE-STD-MIB [11] for this forwarding entry. IPMROUTE-STD-MIB [15] for this forwarding entry.
6.8. Rtg Protocol: 8 bits 6.8. Rtg Protocol: 8 bits
This field describes the routing protocol in use between this router This field describes the routing protocol in use between this router
and the previous-hop router. Specified values include: and the previous-hop router. Specified values include:
0 Unknown 0 Unknown
1 PIM 1 PIM
2 PIM using special routing table 2 PIM using special routing table
3 PIM using a static route 3 PIM using a static route
4 PIM using MBGP route 4 PIM using MBGP route
5 PIM using state created by Assert processing 5 PIM using state created by Assert processing
6 Bi-directional PIM 6 Bi-directional PIM
7 IGMP/MLD proxy 7 IGMP/MLD proxy
8 AMT Relay 8 AMT Relay
9 AMT Gateway 9 AMT Gateway
To obtain these values, multicast routers access to
ipMcastRouteProtocol, ipMcastRouteRtProtocol, and ipMcastRouteRtType
in IpMcastRouteEntry specified in IPMROUTE-STD-MIB [15], and combine
these MIB values to recognize above routing protocol values.
6.9. Fwd TTL: 8 bits 6.9. Fwd TTL: 8 bits
This field contains the TTL that a packet is required to have before This field contains the TTL that a packet is required to have before
it will be forwarded over the outgoing interface. it will be forwarded over the outgoing interface.
6.10. MBZ: 1 bit 6.10. MBZ: 1 bit
Must be zeroed on transmission and ignored on reception. Must be zeroed on transmission and ignored on reception.
6.11. S: 1 bit 6.11. S: 1 bit
skipping to change at page 13, line 45 skipping to change at page 13, line 50
6.12. Src Mask: 6 bits 6.12. Src Mask: 6 bits
This field contains the number of 1's in the netmask this router has This field contains the number of 1's in the netmask this router has
for the source (i.e. a value of 24 means the netmask is 0xffffff00). 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 If the router is forwarding solely on group state, this field is set
to 63 (0x3f). to 63 (0x3f).
6.13. Forwarding Code: 8 bits 6.13. Forwarding Code: 8 bits
This field contains a forwarding information/error code. Section 8.2 This field contains a forwarding information/error code. Section 9.2
explains how and when the forwarding code is filled. Defined values explains how and when the forwarding code is filled. Defined values
are as follows; are as follows;
Value Name Description Value Name Description
----- -------------- ------------------------------------------- ----- -------------- -------------------------------------------
0x00 NO_ERROR No error 0x00 NO_ERROR No error
0x01 WRONG_IF Mtrace2 request arrived on an interface 0x01 WRONG_IF Mtrace2 request arrived on an interface
to which this router would not forward for to which this router would not forward for
this source,group,destination. this source,group,destination.
0x02 PRUNE_SENT This router has sent a prune upstream which 0x02 PRUNE_SENT This router has sent a prune upstream which
applies to the source and group in the applies to the source and group in the
traceroute request. traceroute request.
skipping to change at page 15, line 6 skipping to change at page 15, line 10
response data block in the packet. response data block in the packet.
0x82 OLD_ROUTER The previous-hop router does not understand 0x82 OLD_ROUTER The previous-hop router does not understand
traceroute requests. traceroute requests.
0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited. 0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited.
Note that if a router discovers there is not enough room in a packet Note that if a router discovers there is not enough room in a packet
to insert its response, it puts the 0x81 error code in the previous to insert its response, it puts the 0x81 error code in the previous
router's Forwarding Code field, overwriting any error the previous router's Forwarding Code field, overwriting any error the previous
router placed there. A multicast traceroute client, upon receiving router placed there. After the router sends the response to the
this error, MAY restart the trace at the last hop listed in the Response Address in the header, multicast traceroute client MAY
packet. restart the trace at the last hop listed in the packet (as described
in Section 9.5 and Section 10.1). [TODO: What if the Response
Address is not the address of mtrace2 client?]
The 0x80 bit of the Forwarding Code is used to indicate a fatal The 0x80 bit of the Forwarding Code is used to indicate a fatal
error. A fatal error is one where the router may know the previous error. A fatal error is one where the router may know the previous
hop but cannot forward the message to it. hop but cannot forward the message to it.
7. IPv6 Mtrace2 Response Data 7. IPv6 Mtrace2 Standard Response Block
Each intermediate IPv6 router in a trace path appends "response data" Each intermediate IPv6 router in a trace path appends "response data
to the forwarded trace packet. The response data looks as follows. block" to the forwarded trace packet. The standard response data
block looks as follows.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query Arrival Time | | Query Arrival Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Incoming Interface ID | | Incoming Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outgoing Interface ID | | Outgoing Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 16, line 50 skipping to change at page 16, line 51
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7.1. Query Arrival Time: 32 bits 7.1. Query Arrival Time: 32 bits
Same definition described in Section 6.1 Same definition described in Section 6.1
7.2. Incoming Interface ID: 32 bits 7.2. Incoming Interface ID: 32 bits
This field specifies the interface ID on which packets from this This field specifies the interface ID on which packets from this
source and group are expected to arrive, or 0 if unknown. This ID source and group are expected to arrive, or 0 if unknown. This ID
should be the value taken from InterfaceIndex of the IF-MIB [10] for should be the value taken from InterfaceIndex of the IF-MIB [14] for
this interface. This field is carried in network byte order. this interface. This field is carried in network byte order.
7.3. Outgoing Interface ID: 32 bits 7.3. Outgoing Interface ID: 32 bits
This field specifies the interface ID on which packets from this This field specifies the interface ID on which packets from this
source and group flow to the specified destination, or 0 if unknown. source and group flow to the specified destination, or 0 if unknown.
This ID should be the value taken from InterfaceIndex of the IF-MIB This ID should be the value taken from InterfaceIndex of the IF-MIB
for this interface. This field is carried in network byte order. for this interface. This field is carried in network byte order.
7.4. Local Address 7.4. Local Address
This field specifies a global IPv6 address that uniquely identifies This field specifies a global IPv6 address that uniquely identifies
the router. A unique local unicast address [6] SHOULD NOT be used the router. A unique local unicast address [13] SHOULD NOT be used
unless the node is only assigned link-local and unique local unless the router is only assigned link-local and unique local
addresses. [TBD: What if the node is only assigned link-local addresses. If the router is only assigned link-local addresses, its
addresses? It should be very unlikely case, but is possible even for link-local address can be specified in this field.
a properly working router.]
Note that since interface indices used in the Incoming and Outgoing
Interface ID fields are node-local information, a global identifier
is needed to specify the router.
7.5. Remote Address 7.5. Remote Address
This field specifies the address of the previous-hop router, which, This field specifies the address of the previous-hop router, which,
in most cases, is a link-local unicast address for the queried source in most cases, is a link-local unicast address for the queried source
and destination addresses. and destination addresses.
Although a link-local address does not have enough information to Although a link-local address does not have enough information to
identify a node, it is possible to detect the previous-hop router identify a node, it is possible to detect the previous-hop router
with the assistance of Incoming Interface ID and the current router with the assistance of Incoming Interface ID and the current router
skipping to change at page 19, line 5 skipping to change at page 19, line 5
7.12. Src Prefix Len: 8 bits 7.12. Src Prefix Len: 8 bits
This field contains the prefix length this router has for the source. 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 If the router is forwarding solely on group state, this field is set
to 255 (0xff) to 255 (0xff)
7.13. Forwarding Code: 8 bits 7.13. Forwarding Code: 8 bits
Same definition described in Section 6.13 Same definition described in Section 6.13
8. Router Behavior 8. Mtrace2 Augmented Response Block
In addition to the standard response block, a multicast router on the
path will be able to add "augumented response block" when it sends
the request to its upstream router or sends the response to the
Response Address. This augmented response block is flexible to add
various information.
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 | Value .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The augmented response block is always appended to mtrace2 TLV header
(0x04). The 16 bits Type filed of the augmented response block is
defined for various purposees, such as diagnosis (as in Section 12)
and protocol verification. The packet length of the augmented
response block is specified in the augmented response block TLV
header as see in Section 4.1.
[TODO: Define augmented response block types. Specify how to deal
with diagnosis information.]
9. Router Behavior
All of these actions are performed in addition to (NOT instead of) All of these actions are performed in addition to (NOT instead of)
forwarding the packet, if applicable. E.g. a multicast packet that forwarding the packet, if applicable. E.g. a multicast packet that
has TTL or the hop limit remaining MUST be forwarded normally, as has TTL or the hop limit remaining MUST be forwarded normally, as
MUST a unicast packet that has TTL or the hop limit remaining and is MUST a unicast packet that has TTL or the hop limit remaining and is
not addressed to this router. not addressed to this router.
8.1. Traceroute Query 9.1. Traceroute Query
An mtrace2 Query message is a traceroute message with no response An mtrace2 Query message is a traceroute message with no response
blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 mtrace2. blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 mtrace2.
8.1.1. Packet Verification 9.1.1. Packet Verification
Upon receiving an mtrace2 Query message, a router must examine the Upon receiving an mtrace2 Query message, a router must examine the
Query to see if it is the proper last-hop router for the destination Query to see if it is the proper last-hop router for the destination
address in the packet. It is the proper last-hop router if it has a address in the packet. It is the proper last-hop router if it has a
multicast-capable interface on the same subnet as the Destination multicast-capable interface on the same subnet as the Destination
Address and is the router that would forward traffic from the given Address and is the router that would forward traffic from the given
(S,G) onto that subnet. (S,G) onto that subnet.
If the router determines that it is not the proper last-hop router, If the router determines that it is not the proper last-hop router,
or it cannot make that determination, it does one of two things or it cannot make that determination, it does one of two things
depending if the Query was received via multicast or unicast. If the depending if the Query was received via multicast or unicast. If the
Query was received via multicast, then it MUST be silently dropped. Query was received via multicast, then it MUST be silently dropped.
If it was received via unicast, a forwarding code of WRONG_LAST_HOP If it was received via unicast, a forwarding code of WRONG_LAST_HOP
is noted and processing continues as in Section 8.2 is noted and processing continues as in Section 9.2
Duplicate Query messages as identified by the tuple (IP Source, Query Duplicate Query messages as identified by the tuple (IP Source, Query
ID) SHOULD be ignored. This MAY be implemented using a simple 1-back ID) SHOULD be ignored. This MAY be implemented using a simple 1-back
cache (i.e. remembering the IP source and Query ID of the previous cache (i.e. remembering the IP source and Query ID of the previous
Query message that was processed, and ignoring future messages with Query message that was processed, and ignoring future messages with
the same IP Source and Query ID). Duplicate Request messages MUST the same IP Source and Query ID). Duplicate Request messages MUST
NOT be ignored in this manner. NOT be ignored in this manner.
8.1.2. Normal Processing 9.1.2. Normal Processing
When a router receives an mtrace2 Query and it determines that it is When a router receives an mtrace2 Query and it determines that it is
the proper last-hop router, it treats it like an mtrace2 Request and the proper last-hop router, it treats it like an mtrace2 Request and
performs the steps listed in Section 8.2 performs the steps listed in Section 9.2
8.2. Mtrace2 Request 9.2. Mtrace2 Request
An mtrace2 Request is a traceroute message with some number of An mtrace2 Request is a traceroute message with some number of
response blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 response blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6
mtrace2. Routers can tell the difference between Queries and mtrace2. Routers can tell the difference between Queries and
Requests by checking the length of the packet. Requests by checking the length of the packet.
8.2.1. Packet Verification 9.2.1. Packet Verification
If the mtrace2 Request is not addressed to this router, or if the 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 Request is addressed to a multicast group which is not a link-scoped
group (i.e. 224/24 for IPv4, FFx2::/16 [3] for IPv6), it MUST be group (i.e. 224/24 for IPv4, FFx2::/16 [3] for IPv6), it MUST be
silently ignored. silently ignored.
8.2.2. Normal Processing 9.2.2. Normal Processing
When a router receives an mtrace2 Request, it performs the following When a router receives an mtrace2 Request, it performs the following
steps. Note that it is possible to have multiple situations covered steps. Note that it is possible to have multiple situations covered
by the Forwarding Codes. The first one encountered is the one that by the Forwarding Codes. The first one encountered is the one that
is reported, i.e. all "note forwarding code N" should be interpreted is reported, i.e. all "note forwarding code N" should be interpreted
as "if forwarding code is not already set, set forwarding code to N". as "if forwarding code is not already set, set forwarding code to N".
1. If there is room in the current buffer (or the router can 1. If there is room in the current buffer (or the router can
efficiently allocate more space to use), insert a new response efficiently allocate more space to use), insert a new response
block into the packet and fill in the Query Arrival Time, block into the packet and fill in the Query Arrival Time,
Outgoing Interface Address (for IPv4 mtrace2) or Outgoing Outgoing Interface Address (for IPv4 mtrace2) or Outgoing
Interface ID (for IPv6 mtrace2), Output Packet Count, and Fwd Interface ID (for IPv6 mtrace2), Output Packet Count, and Fwd
TTL (for IPv4 mtrace2). If there was no room, fill in the TTL (for IPv4 mtrace2). If there was no room, fill in the
response code "NO_SPACE" in the *previous* hop's response block, response code "NO_SPACE" in the *previous* hop's response block,
and forward the packet to the requester as described in and forward the packet to the requester as described in
Section 8.4. Section 9.4.
2. Attempt to determine the forwarding information for the source 2. Attempt to determine the forwarding information for the source
and group specified, using the same mechanisms as would be used and group specified, using the same mechanisms as would be used
when a packet is received from the source destined for the when a packet is received from the source destined for the
group. State need not be instantiated, it can be "phantom" group. State need not be instantiated, it can be "phantom"
state created only for the purpose of the trace. state created only for the purpose of the trace, such as "dry-
run".
If using a shared-tree protocol and there is no source-specific If using a shared-tree protocol and there is no source-specific
state, or if the source is specified as "all 1", group state state, or if the source is specified as "all 1", group state
should be used. If there is no group state or the group is should be used. If there is no group state or the group is
specified as 0, potential source state (i.e. the path that would specified as 0, potential source state (i.e. the path that would
be followed for a source-specific Join) should be used. If this be followed for a source-specific Join) should be used. If this
router is the Core or RP and no source-specific information is router is the Core or RP and no source-specific information is
available, note an error code of REACHED_RP. available, note an error code of REACHED_RP.
3. If no forwarding information can be determined, the router notes 3. If no forwarding information can be determined, the router notes
an error code of NO_ROUTE, sets the remaining fields that have an error code of NO_ROUTE, sets the remaining fields that have
not yet been filled in to zero, and then forwards the packet to not yet been filled in to zero, and then forwards the packet to
the requester as described in Section 8.4. the requester as described in Section 9.4.
4. Fill in the Incoming Interface Address, Previous-Hop Router 4. Fill in the Incoming Interface Address, Previous-Hop Router
Address, Input Packet Count, Total Number of Packets, Routing Address, Input Packet Count, Total Number of Packets, Routing
Protocol, S, and Src Mask from the forwarding information that Protocol, S, and Src Mask from the forwarding information that
was determined. was determined.
5. If traceroute is administratively prohibited or the previous hop 5. If mtrace2 is administratively prohibited or the previous hop
router does not understand traceroute requests, note the router does not understand mtrace2 requests, note the
appropriate forwarding code (ADMIN_PROHIB or OLD_ROUTER). If appropriate forwarding code (ADMIN_PROHIB or OLD_ROUTER). If
traceroute is administratively prohibited and any of the fields mtrace2 is administratively prohibited and any of the fields as
as filled in step 4 are considered private information, zero out filled in step 4 are considered private information, zero out
the applicable fields. Then the packet is forwarded to the the applicable fields. Then the packet is forwarded to the
requester as described in Section 8.4. requester as described in Section 9.4.
6. If the reception interface is not enabled for multicast, note 6. If the reception interface is not enabled for multicast, note
forwarding code NO_MULTICAST. If the reception interface is the forwarding code NO_MULTICAST. If the reception interface is the
interface from which the router would expect data to arrive from interface from which the router would expect data to arrive from
the source, note forwarding code RPF_IF. Otherwise, if the the source, note forwarding code RPF_IF. Otherwise, if the
reception interface is not one to which the router would forward reception interface is not one to which the router would forward
data from the source to the group, a forwarding code of WRONG_IF data from the source to the group, a forwarding code of WRONG_IF
is noted. is noted.
7. If the group is subject to administrative scoping on either the 7. If the group is subject to administrative scoping on either the
Outgoing or Incoming interfaces, a forwarding code of SCOPED is Outgoing or Incoming interfaces, a forwarding code of SCOPED is
noted. noted.
8. If this router is the Rendezvous Point or Core for the group, a 8. If this router is the Rendezvous Point or Core for the group, a
forwarding code of REACHED_RP is noted. forwarding code of REACHED_RP is noted.
9. If this router has sent a prune upstream which applies to the 9. If this router has sent a prune upstream which applies to the
source and group in the traceroute Request, it notes forwarding source and group in the mtrace2 Request, it notes forwarding
code PRUNE_SENT. If the router has stopped forwarding code PRUNE_SENT. If the router has stopped forwarding
downstream in response to a prune sent by the next hop router, downstream in response to a prune sent by the next hop router,
it notes forwarding code PRUNE_RCVD. If the router should it notes forwarding code PRUNE_RCVD. If the router should
normally forward traffic for this source and group downstream normally forward traffic for this source and group downstream
but is not, it notes forwarding code NOT_FORWARDING. but is not, it notes forwarding code NOT_FORWARDING.
10. The packet is then sent on to the previous hop or the requester 10. The packet is then sent on to the previous hop or the requester
as described in Section 8.4. as described in Section 9.4.
8.3. Mtrace2 Response 9.3. Mtrace2 Response
A router must forward all mtrace2 response packets normally, with no A router must forward all mtrace2 response packets normally, with no
special processing. If a router has initiated an mtrace2 with a special processing. If a router has initiated an mtrace2 with a
Query or Request message, it may listen for Responses to that Query or Request message, it may listen for Responses to that
traceroute but MUST still forward them as well. traceroute and MUST forward them as well.
8.4. Forwarding Mtrace2 Requests 9.4. Forwarding Mtrace2 Requests
If the Previous-hop router is known for this request, the packet is If the Previous-hop router is known for this request and the number
sent to that router. If the Incoming Interface is known but the of response blocks is less than the number requested (i.e., the "#
Previous-hop router is not known, the packet is sent to an hops" field in mtrace2 header), the packet is sent to that router.
appropriate multicast address on the Incoming Interface. The
appropriate multicast address may depend on the routing protocol in
use, MUST be a link-scoped group (i.e. 224/24 for IPv4, FF02::/16 for
IPv6), MUST NOT be ALL-SYSTEMS.MCAST.NET (224.0.0.1) for IPv4 and All
Nodes Address (FF02::1) for IPv6, and MAY be ALL-ROUTERS.MCAST.NET
(224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6 if the
routing protocol in use does not define a more appropriate group.
Otherwise, it is sent to the Response Address in the header, as
described in Section 8.5.
8.5. Sending Mtrace2 Responses If the Incoming Interface is known but the Previous-hop router is not
known, the packet is sent to an appropriate multicast address on the
Incoming Interface. The appropriate multicast address may depend on
the routing protocol in use, MUST be a link-scoped group (i.e. 224/24
for IPv4, FF02::/16 for IPv6), MUST NOT be ALL-SYSTEMS.MCAST.NET
(224.0.0.1) for IPv4 and All Nodes Address (FF02::1) for IPv6, and
MAY be ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers
Address (FF02::2) for IPv6 if the routing protocol in use does not
define a more appropriate group. Otherwise, it is sent to the
Response Address in the header, as described in Section 9.5.
8.5.1. Destination Address 9.5. Sending Mtrace2 Responses
9.5.1. Destination Address
An mtrace2 response must be sent to the Response Address in the An mtrace2 response must be sent to the Response Address in the
traceroute header. mtrace2 header.
8.5.2. TTL and Hop Limit 9.5.2. TTL and Hop Limit
If the Response Address is unicast, the router inserts its normal If the Response Address is unicast, the router inserts its normal
unicast TTL or hop limit in the IP header. If the Response Address unicast TTL or hop limit in the IP header. If the Response Address
is multicast, the router copies the Response TTL or hop limit from is multicast, the router copies the Response TTL or hop limit from
the traceroute header into the IP header. the mtrace2 header into the IP header.
8.5.3. Source Address 9.5.3. Source Address
If the Response Address is unicast, the router may use any of its If the Response Address is unicast, the router may use any of its
interface addresses as the source address. Since some multicast interface addresses as the source address. Since some multicast
routing protocols forward based on source address, if the Response routing protocols forward based on source address, if the Response
Address is multicast, the router MUST use an address that is known in Address is multicast, the router MUST use an address that is known in
the multicast routing topology if it can make that determination. the multicast routing topology if it can make that determination.
8.5.4. Sourcing Multicast Responses 9.5.4. Sourcing Multicast Responses
When a router sources a multicast response, the response packet MUST When a router sources a multicast response, the response packet MUST
be sent on a single interface, then forwarded as if it were received be sent on a single interface, then forwarded as if it were received
on that interface. It MUST NOT source the response packet on that interface. It MUST NOT source the response packet
individually on each interface, in order to avoid duplicate packets. individually on each interface, in order to avoid duplicate packets.
8.6. Hiding Information 9.6. Hiding Information
Information about a domain's topology and connectivity may be hidden Information about a domain's topology and connectivity may be hidden
from multicast traceroute requests. The exact mechanism is not from multicast traceroute requests. The exact mechanism is not
specified here; however, the INFO_HIDDEN forwarding code may be used specified here; however, the INFO_HIDDEN forwarding code may be used
to note that, for example, the incoming interface address and packet to note that, for example, the incoming interface address and packet
count are for the entrance to the domain and the outgoing interface count are for the entrance to the domain and the outgoing interface
address and packet count are the exit from the domain. The source- address and packet count are the exit from the domain. The source-
group packet count may be from either router or not specified (all group packet count may be from either router or not specified (all
1). 1).
9. Client Behavior 10. Client Behavior
9.1. Sending Mtrace2 Query 10.1. Sending Mtrace2 Query
When the destination of the mtrace2 is the machine running the When the destination of the mtrace2 is the machine running the
client, the mtrace2 Query packet can be sent to the ALL- client, the mtrace2 Query packet can be sent to the ALL-
ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers Address 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 (FF02::2) for IPv6. This will ensure that the packet is received by
the last-hop router on the subnet. Otherwise, if the proper last-hop the last-hop router on the subnet. Otherwise, if the proper last-hop
router is known for the mtrace2 destination, the Query could be router is known for the mtrace2 destination, or if the mtrace2 client
unicasted to that router. Otherwise, the Query packet should be wants to restart mtrace2 Query from the intermediate router that
multicasted to the group being queried; if the destination of the responded with NO_SPACE in Forwarding Code of Standard Response Block
mtrace2 is a member of the group, this will get the Query to the as specified in Section 6.13, the Query could be unicasted to that
proper last-hop router. In this final case, the packet should router. Otherwise, the Query packet should be multicasted to the
contain the Router Alert option [8][9], to make sure that routers group being queried; if the destination of the mtrace2 is a member of
that are not members of the multicast group notice the packet. the group, this will get the Query to the proper last-hop router. In
this final case, the packet should contain the Router Alert option
[7][8], to make sure that routers that are not members of the
multicast group notice the packet.
See also Section 9.4 on determining the last-hop router. See also Section 10.4 on determining the last-hop router.
9.2. Determining the Path 10.2. Determining the Path
The client could send a small number of initial query messages with a The client could send a small number of initial query messages with a
large "# hops" field, in order to try to trace the full path. If large "# hops" field, in order to try to trace the full path. If
this attempt fails, one strategy is to perform a linear search (as this attempt fails, one strategy is to perform a linear search (as
the traditional unicast traceroute program does); set the "# hops" the traditional unicast traceroute program does); set the "# hops"
field to 1 and try to get a response, then 2, and so on. If no field to 1 and try to get a response, then 2, and so on. If no
response is received at a certain hop, the hop count can continue response is received at a certain hop, the hop count can continue
past the non-responding hop, in the hopes that further hops may past the non-responding hop, in the hopes that further hops may
respond. These attempts should continue until a user-defined timeout respond. These attempts should continue until a user-defined timeout
has occurred. has occurred.
See also Section 9.5 and Section 9.6 on receiving the results of a See also Section 10.5 and Section 10.6 on receiving the results of a
trace. trace.
9.3. Collecting Statistics 10.3. Collecting Statistics
After a client has determined that it has traced the whole path or as After a client has determined that it has traced the whole path or as
much as it can expect to (see Section 9.7), it might collect much as it can expect to (see Section 10.7), it might collect
statistics by waiting a short time and performing a second trace. If statistics by waiting a short time and performing a second trace. If
the path is the same in the two traces, statistics can be displayed the path is the same in the two traces, statistics can be displayed
as described in Section 11.3 and Section 11.4. as described in Section 12.3 and Section 12.4.
9.4. Last Hop Router 10.4. Last Hop Router
The mtrace2 querier may not know which is the last hop router, or The mtrace2 querier may not know which is the last hop router, or
that router may be behind a firewall that blocks unicast packets but that router may be behind a firewall that blocks unicast packets but
passes multicast packets. In these cases, the mtrace2 request should passes multicast packets. In these cases, the mtrace2 request should
be multicasted to ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All be multicasted to ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All
Routers Address (FF02::2) for IPv6. All routers except the correct Routers Address (FF02::2) for IPv6. All routers except the correct
last hop router should ignore any mtrace2 request received via last hop router should ignore any mtrace2 request received via
multicast. Mtrace2 requests which are multicasted to the group being multicast. Mtrace2 requests which are multicasted to the group being
traced must include the Router Alert option[8][9]. traced must include the Router Alert option[7][8].
Another alternative is to unicast to the trace destination. Mtrace2 Another alternative is to unicast to the trace destination. Mtrace2
requests which are unicasted to the trace destination must include requests which are unicasted to the trace destination must include
the Router Alert option, in order that the last-hop router is aware the Router Alert option, in order that the last-hop router is aware
of the packet. of the packet.
9.5. First Hop Router 10.5. First Hop Router
The mtrace2 querier may not be unicast reachable from the first hop The mtrace2 querier may not be unicast reachable from the first hop
router. In this case, the querier should set the traceroute response router. In this case, the querier should set the mtrace2 response
address to a multicast address, and should set the response TTL (or address to a multicast address, and should set the response TTL (or
hop limit) to a value sufficient for the response from the first hop hop limit) to a value sufficient for the response from the first hop
router to reach the querier. It may be appropriate to start with a router to reach the querier. It may be appropriate to start with a
small TTL and increase in subsequent attempts until a sufficient TTL small TTL and increase in subsequent attempts until a sufficient TTL
is reached, up to an appropriate maximum (such as 192). is reached, up to an appropriate maximum (such as 192).
The IANA has assigned 224.0.1.32, MTRACE.MCAST.NET as the default The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default
multicast group for IPv4 mtrace2 responses, and will assign multicast group for IPv4 mtrace responses. However, mtrace2 does not
MTRACE2_IPV6RESPADDR (TBD (see Section 12)) for IPv6 mtrace2 reserve any IPv4/IPv6 multicast addresses for mtrace2 responses,
responses. Other groups may be used if needed, e.g. when using because mtrace2 does not send its responses with multicast.
mtrace2 to diagnose problems with the IANA-assigned group.
9.6. Broken Intermediate Router 10.6. Broken Intermediate Router
A broken intermediate router might simply not understand traceroute A broken intermediate router might simply not understand mtrace2
packets, and drop them. The querier would then get no response at packets, and drop them. The querier would then get no response at
all from its traceroute requests. It should then perform a hop-by- all from its mtrace2 requests. It should then perform a hop-by-hop
hop search by setting the number of responses field until it gets a search by setting the number of responses field until it gets a
response (both linear and binary search are options, but binary is response (both linear and binary search are options, but binary is
likely to be slower because a failure requires waiting for a likely to be slower because a failure requires waiting for a
timeout). timeout).
9.7. Mtrace2 Termination 10.7. Mtrace2 Termination
When performing an expanding hop-by-hop trace, it is necessary to When performing an expanding hop-by-hop trace, it is necessary to
determine when to stop expanding. determine when to stop expanding.
9.7.1. Arriving at source 10.7.1. Arriving at source
A trace can be determined to have arrived at the source if the A trace can be determined to have arrived at the source if the
Incoming Interface of the last router in the trace is non-zero, but Incoming Interface of the last router in the trace is non-zero, but
the Previous Hop router is zero. the Previous Hop router is zero.
9.7.2. Fatal error 10.7.2. Fatal error
A trace has encountered a fatal error if the last Forwarding Error in A trace has encountered a fatal error if the last Forwarding Error in
the trace has the 0x80 bit set. the trace has the 0x80 bit set.
9.7.3. No previous hop 10.7.3. No previous hop
A trace can not continue if the last Previous Hop in the trace is set A trace can not continue if the last Previous Hop in the trace is set
to 0. to 0.
9.7.4. Traceroute shorter than requested 10.7.4. Traceroute shorter than requested
If the trace that is returned is shorter than requested (i.e. the If the trace that is returned is shorter than requested (i.e. the
number of Response blocks is smaller than the "# hops" field), the number of response blocks is smaller than the "# hops" field), the
trace encountered an error and could not continue. trace encountered an error and could not continue.
9.8. Continuing after an error 10.8. Continuing after an error
When the NO_SPACE error occurs, the client might try to continue the When the NO_SPACE error occurs, the client might try to continue the
trace by starting it at the last hop in the trace. It can do this by trace by starting it at the last hop in the trace. It can do this by
unicasting to this router's outgoing interface address, keeping all unicasting to this router's outgoing interface address, keeping all
fields the same. If this results in a single hop and a "WRONG_IF" fields the same. If this results in a single hop and a "WRONG_IF"
error, the client may try setting the trace destination to the same error, the client may try setting the trace destination to the same
outgoing interface address. outgoing interface address.
If a trace times out, it is likely to be because a router in the If a trace times out, it is likely to be because a router in the
middle of the path does not support multicast traceroute. That middle of the path does not support multicast traceroute. That
router's address will be in the Previous Hop field of the last entry router's address will be in the Previous Hop field of the last entry
in the last response packet received. A client may be able to in the last response packet received. A client may be able to
determine (via mrinfo or SNMP [6][11]) a list of neighbors of the determine (via mrinfo or SNMP [13][15]) a list of neighbors of the
non-responding router. If desired, each of those neighbors could be non-responding router. If desired, each of those neighbors could be
probed to determine the remainder of the path. Unfortunately, this probed to determine the remainder of the path. Unfortunately, this
heuristic may end up with multiple paths, since there is no way of heuristic may end up with multiple paths, since there is no way of
knowing what the non-responding router's algorithm for choosing a knowing what the non-responding router's algorithm for choosing a
previous-hop router is. However, if all paths but one flow back previous-hop router is. However, if all paths but one flow back
towards the non-responding router, it is possible to be sure that towards the non-responding router, it is possible to be sure that
this is the correct path. this is the correct path.
10. Protocol-Specific Considerations 11. Protocol-Specific Considerations
10.1. PIM-SM 11.1. PIM-SM
When a multicast traceroute reaches a PIM-SM RP and the RP does not When a multicast traceroute reaches a PIM-SM RP and the RP does not
forward the trace on, it means that the RP has not performed a 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, 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- 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 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. RP, the trace source to the traffic source, and the trace group to 0.
This trace Query may be unicasted to the RP. This trace Query may be unicasted to the RP.
10.2. Bi-Directional PIM 11.2. Bi-Directional PIM
Bi-directional PIM [13] is a variant of PIM-SM that builds bi- Bi-directional PIM [10] is a variant of PIM-SM that builds bi-
directional shared trees connecting multicast sources and receivers. directional shared trees connecting multicast sources and receivers.
Along the bi-directional shared trees, multicast data is natively Along the bi-directional shared trees, multicast data is natively
forwarded from sources to the RPA (Rendezvous Point Address) and from forwarded from sources to the RPA (Rendezvous Point Address) and from
the RPA to receivers without requiring source-specific state. In the RPA to receivers without requiring source-specific state. In
contrast to PIM-SM, RP always has the state to trace. contrast to PIM-SM, RP always has the state to trace.
A Designated Forwarder (DF) for a given RPA is in charge of A Designated Forwarder (DF) for a given RPA is in charge of
forwarding downstream traffic onto its link, and forwarding upstream forwarding downstream traffic onto its link, and forwarding upstream
traffic from its link towards the RPL (Rendezvous Point Link) that traffic from its link towards the RPL (Rendezvous Point Link) that
the RPA belongs to. Hence mtrace2 reports DF addresses or RPA along the RPA belongs to. Hence mtrace2 reports DF addresses or RPA along
the path. the path.
10.3. PIM-DM 11.3. PIM-DM
Routers running PIM Dense Mode do not know the path packets would Routers running PIM Dense Mode do not know the path packets would
take unless traffic is flowing. Without some extra protocol take unless traffic is flowing. Without some extra protocol
mechanism, this means that in an environment with multiple possible mechanism, this means that in an environment with multiple possible
paths with branch points on shared media, multicast traceroute can paths with branch points on shared media, multicast traceroute can
only trace existing paths, not potential paths. When there are only trace existing paths, not potential paths. When there are
multiple possible paths but the branch points are not on shared multiple possible paths but the branch points are not on shared
media, the previous hop router is known, but the last hop router may media, the previous hop router is known, but the last hop router may
not know that it is the appropriate last hop. not know that it is the appropriate last hop.
When traffic is flowing, PIM Dense Mode routers know whether or not When traffic is flowing, PIM Dense Mode routers know whether or not
they are the last-hop forwarder for the link (because they won or they are the last-hop forwarder for the link (because they won or
lost an Assert battle) and know who the previous hop is (because it lost an Assert battle) and know who the previous hop is (because it
won an Assert battle). Therefore, multicast traceroute is always won an Assert battle). Therefore, multicast traceroute is always
able to follow the proper path when traffic is flowing. able to follow the proper path when traffic is flowing.
10.4. IGMP/MLD Proxy 11.4. IGMP/MLD Proxy
When a mtrace2 Query packet reaches an incoming interface of IGMP/MLD When a mtrace2 Query packet reaches an incoming interface of IGMP/MLD
Proxy [14], it must be simply discarded. When a mtrace2 Query packet Proxy [11], it put a WRONG_IF (0x01) value in Forwarding Code of
reaches an outgoing interface of IGMP/MLD Proxy, it is forwarded mtrace2 standard response block (as in Section 6.13) and sends the
through its incoming interface towards the upstream router. mtrace2 response back to the Response Address. When a mtrace2 Query
packet reaches an outgoing interface of IGMP/MLD Proxy, it is
forwarded through its incoming interface towards the upstream router.
10.5. AMT 11.5. AMT
AMT [15] provides the multicast connectivity to the unicast-only AMT [12] provides the multicast connectivity to the unicast-only
inter-network. To do this, multicast packets being sent to or from a inter-network. To do this, multicast packets being sent to or from a
site are encapsulated in unicast packets. When a mtrace2 Query site are encapsulated in unicast packets. When a mtrace2 Query
packet reaches an AMT Pseudo-Interface of an AMT Gateway, the AMT packet reaches an AMT Pseudo-Interface of an AMT Gateway, the AMT
Gateway encapsulats it to a particular AMT Relay reachable across the Gateway encapsulats it to a particular AMT Relay reachable across the
unicast-only infrastructure. unicast-only infrastructure.
11. Problem Diagnosis 12. Problem Diagnosis
11.1. Forwarding Inconsistencies 12.1. Forwarding Inconsistencies
The forwarding error code can tell if a group is unexpectedly pruned The forwarding error code can tell if a group is unexpectedly pruned
or administratively scoped. or administratively scoped.
11.2. TTL or Hop Limit Problems 12.2. TTL or Hop Limit Problems
By taking the maximum of hops (from source + forwarding TTL (or hop By taking the maximum of hops (from source + forwarding TTL (or hop
limit) threshold) over all hops, you can discover the TTL or hop limit) threshold) over all hops, it is possible to discover the TTL
limit required for the source to reach the destination. or hop limit required for the source to reach the destination.
11.3. Packet loss 12.3. Packet loss
By taking two traces, you can find packet loss information by By taking two traces, it is possible to find packet loss information
comparing the difference in input packet counts to the difference in by comparing the difference in input packet counts to the difference
output packet counts for the specified source-group address pair at in output packet counts for the specified source-group address pair
the previous hop. On a point-to-point link, any difference in these at the previous hop. On a point-to-point link, any difference in
numbers implies packet loss. Since the packet counts may be changing these numbers implies packet loss. Since the packet counts may be
as the mtrace2 query is propagating, there may be small errors (off changing as the mtrace2 query is propagating, there may be small
by 1 or 2 or more) in these statistics. However, these errors will errors (off by 1 or 2 or more) in these statistics. However, these
not accumulate if multiple traces are taken to expand the measurement errors will not accumulate if multiple traces are taken to expand the
period. On a shared link, the count of input packets can be larger measurement period. On a shared link, the count of input packets can
than the number of output packets at the previous hop, due to other be larger than the number of output packets at the previous hop, due
routers or hosts on the link injecting packets. This appears as to other routers or hosts on the link injecting packets. This
"negative loss" which may mask real packet loss. appears as "negative loss" which may mask real packet loss.
In addition to the counts of input and output packets for all In addition to the counts of input and output packets for all
multicast traffic on the interfaces, the response data includes a multicast traffic on the interfaces, the response data includes a
count of the packets forwarded by a node for the specified source- count of the packets forwarded by a node for the specified source-
group pair. Taking the difference in this count between two traces group pair. Taking the difference in this count between two traces
and then comparing those differences between two hops gives a measure and then comparing those differences between two hops gives a measure
of packet loss just for traffic from the specified source to the of packet loss just for traffic from the specified source to the
specified receiver via the specified group. This measure is not specified receiver via the specified group. This measure is not
affected by shared links. affected by shared links.
On a point-to-point link that is a multicast tunnel, packet loss is On a point-to-point link that is a multicast tunnel, packet loss is
usually due to congestion in unicast routers along the path of that usually due to congestion in unicast routers along the path of that
tunnel. On native multicast links, loss is more likely in the output tunnel. On native multicast links, loss is more likely in the output
queue of one hop, perhaps due to priority dropping, or in the input queue of one hop, perhaps due to priority dropping, or in the input
queue at the next hop. The counters in the response data do not queue at the next hop. The counters in the response data do not
allow these cases to be distinguished. Differences in packet counts allow these cases to be distinguished. Differences in packet counts
between the incoming and outgoing interfaces on one node cannot between the incoming and outgoing interfaces on one node cannot
generally be used to measure queue overflow in the node. generally be used to measure queue overflow in the node.
11.4. Link Utilization 12.4. Link Utilization
Again, with two traces, you can divide the difference in the input or Again, with two traces, you can divide the difference in the input or
output packet counts at some hop by the difference in time stamps output packet counts at some hop by the difference in time stamps
from the same hop to obtain the packet rate over the link. If the from the same hop to obtain the packet rate over the link. If the
average packet size is known, then the link utilization can also be average packet size is known, then the link utilization can also be
estimated to see whether packet loss may be due to the rate limit or estimated to see whether packet loss may be due to the rate limit or
the physical capacity on a particular link being exceeded. the physical capacity on a particular link being exceeded.
11.5. Time Delay 12.5. Time Delay
If the routers have synchronized clocks, it is possible to estimate If the routers have synchronized clocks, it is possible to estimate
propagation and queuing delay from the differences between the propagation and queuing delay from the differences between the
timestamps at successive hops. However, this delay includes control timestamps at successive hops. However, this delay includes control
processing overhead, so is not necessarily indicative of the delay processing overhead, so is not necessarily indicative of the delay
that data traffic would experience. that data traffic would experience.
12. IANA Considerations 13. IANA Considerations
The following new assignments can only be made via a Standards Action The following new assignments can only be made via a Standards Action
as specified in [5]. as specified in [5].
12.1. Forwarding Codes 13.1. Forwarding Codes
New Forwarding codes must only be created by an RFC that modifies New Forwarding codes must only be created by an RFC that modifies
this document's Section 9, fully describing the conditions under this document's Section 10, fully describing the conditions under
which the new forwarding code is used. The IANA may act as a central 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 repository so that there is a single place to look up forwarding
codes and the document in which they are defined. codes and the document in which they are defined.
12.2. UDP Destination Port and IPv6 Address 13.2. UDP Destination Port and IPv6 Address
The IANA should allocate UDP destination port for multicast The IANA should allocate UDP destination port for multicast
traceroute version 2 upon publication of the first RFC. traceroute version 2 upon publication of the first RFC.
Additionally, the well-known multicast address (MTRACE2_IPV6RESPADDR)
intended for default use by IPv6 multicast traceroute should be
registered and defined by the first RFC published.
13. Security Considerations 14. Security Considerations
13.1. Topology Discovery 14.1. Topology Discovery
Mtrace2 can be used to discover any actively-used topology. If your Mtrace2 can be used to discover any actively-used topology. If your
network topology is a secret, mtrace2 may be restricted at the border network topology is a secret, mtrace2 may be restricted at the border
of your domain, using the ADMIN_PROHIB forwarding code. of your domain, using the ADMIN_PROHIB forwarding code.
13.2. Traffic Rates 14.2. Traffic Rates
Mtrace2 can be used to discover what sources are sending to what Mtrace2 can be used to discover what sources are sending to what
groups and at what rates. If this information is a secret, mtrace2 groups and at what rates. If this information is a secret, mtrace2
may be restricted at the border of your domain, using the may be restricted at the border of your domain, using the
ADMIN_PROHIB forwarding code. ADMIN_PROHIB forwarding code.
13.3. Unicast Replies 14.3. Unicast Replies
The "Response address" field may be used to send a single packet (the The "Response address" field may be used to send a single packet (the
traceroute Reply packet) to an arbitrary unicast address. It is mtrace2 Reply packet) to an arbitrary unicast address. It is
possible to use this facility as a packet amplifier, as a small possible to use this facility as a packet amplifier, as a small
multicast traceroute Query may turn into a large Reply packet. multicast traceroute Query may turn into a large Reply packet.
14. Acknowledgements 15. Acknowledgements
This specification started largely as a transcription of Van This specification started largely as a transcription of Van
Jacobson's slides from the 30th IETF, and the implementation in Jacobson's slides from the 30th IETF, and the implementation in
mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve
Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original
multicast traceroute client, mtrace (version 1), has been implemented multicast traceroute client, mtrace (version 1), has been implemented
by Ajit Thyagarajan, Steve Casner and Bill Fenner. by Ajit Thyagarajan, Steve Casner and Bill Fenner.
The idea of unicasting a multicast traceroute Query to the The idea of unicasting a multicast traceroute Query to the
destination of the trace with Router Alert set is due to Tony destination of the trace with Router Alert set is due to Tony
Ballardie. The idea of the "S" bit to allow statistics for a source Ballardie. The idea of the "S" bit to allow statistics for a source
subnet is due to Tom Pusateri. subnet is due to Tom Pusateri.
For the mtrace version 2 specification, extensive comments were For the mtrace version 2 specification, extensive comments were
received from Yiqun Cai, Liu Hui, Bharat Joshi, Shinsuke Suzuki, and received from Yiqun Cai, Liu Hui, Bharat Joshi, Shinsuke Suzuki,
Cao Wei. Achmad Husni Thamrin, and Cao Wei.
15. References 16. References
15.1. Normative References 16.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to indicate requirement [1] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", RFC 2119, March 1997. levels", RFC 2119, March 1997.
[2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998. Specification", RFC 2460, December 1998.
[3] Hinden, R. and S. Deering, "IP Version 6 Addressing [3] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998. Architecture", RFC 2373, July 1998.
[4] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. [4] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version 3", Thyagarajan, "Internet Group Management Protocol, Version 3",
RFC 3376, October 2002. RFC 3376, October 2002.
[5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA [5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 2434, October 1998. Considerations Section in RFCs", RFC 2434, October 1998.
15.2. Informative References [6] Braden, B., Borman, D., and C. Partridge, "Computing the
[6] Draves, R. and D. Thaler, "Default Router Preferences and More-
Specific Routes", RFC 4191, November 2005.
[7] Braden, B., Borman, D., and C. Partridge, "Computing the
Internet Checksum", RFC 1071, September 1988. Internet Checksum", RFC 1071, September 1988.
[8] Katz, D., "IP Router Alert Option", RFC 2113, February 1997. [7] Katz, D., "IP Router Alert Option", RFC 2113, February 1997.
[9] Partridge, C. and A. Jackson, "IPv6 Router Alert Option", [8] Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
RFC 2711, October 1999. RFC 2711, October 1999.
[10] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", [9] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
RFC 2863, June 2000.
[11] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB",
draft-ietf-mboned-ip-mcast-mib-05.txt (work in progress),
March 2007.
[12] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM): "Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006. Protocol Specification (Revised)", RFC 4601, August 2006.
[13] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, [10] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-PIM)", "Bidirectional Protocol Independent Multicast (BIDIR-PIM)",
RFC 5015, October 2007. RFC 5015, October 2007.
[14] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet [11] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet
Group Management Protocol (IGMP) / Multicast Listener Discovery Group Management Protocol (IGMP) / Multicast Listener Discovery
(MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")",
RFC 4605, August 2006. RFC 4605, August 2006.
[15] Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T. [12] Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T.
Pusateri, "Automatic IP Multicast Without Explicit Tunnels Pusateri, "Automatic IP Multicast Without Explicit Tunnels
(AMT)", draft-ietf-mboned-auto-multicast-08.txt (work in (AMT)", draft-ietf-mboned-auto-multicast-08.txt (work in
progress), October 2007. progress), October 2007.
16.2. Informative References
[13] Draves, R. and D. Thaler, "Default Router Preferences and More-
Specific Routes", RFC 4191, November 2005.
[14] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB",
RFC 2863, June 2000.
[15] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB",
RFC 5132, December 2007.
Authors' Addresses Authors' Addresses
Hitoshi Asaeda Hitoshi Asaeda
Keio University Keio University
Graduate School of Media and Governance Graduate School of Media and Governance
Fujisawa, Kanagawa 252-8520 Fujisawa, Kanagawa 252-8520
Japan Japan
Email: asaeda@wide.ad.jp Email: asaeda@wide.ad.jp
URI: http://www.sfc.wide.ad.jp/~asaeda/
Tatuya Jinmei Tatuya Jinmei
Internet Systems Consortium Internet Systems Consortium
Redwood City, CA 94063 Redwood City, CA 94063
US US
Email: Jinmei_Tatuya@isc.org Email: Jinmei_Tatuya@isc.org
William C. Fenner William C. Fenner
Arastra, Inc. Arastra, Inc.
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