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Versions: (draft-asaeda-mboned-mtrace-v2) 00
01 02 03 04 05 06 07 08 09 10 11 12
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MBONED Working Group H. Asaeda
Internet-Draft Keio University
Intended status: Standards Track T. Jinmei
Expires: January 14, 2010 ISC
W. Fenner
Arastra, Inc.
S. Casner
Packet Design, Inc.
July 13, 2009
Mtrace Version 2: Traceroute Facility for IP Multicast
draft-ietf-mboned-mtrace-v2-04
Status of this Memo
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Copyright Notice
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Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Abstract
This document describes the IP multicast traceroute facility. Unlike
unicast traceroute, multicast traceroute requires special
implementations on the part of routers. This specification describes
the required functionality in multicast routers, as well as how
management applications can use the router functionality.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 9
4.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 9
5. Mtrace2 Query Header . . . . . . . . . . . . . . . . . . . . . 10
5.1. # hops: 8 bits . . . . . . . . . . . . . . . . . . . . . . 10
5.2. Multicast Address . . . . . . . . . . . . . . . . . . . . 10
5.3. Source Address . . . . . . . . . . . . . . . . . . . . . . 11
5.4. Destination Address . . . . . . . . . . . . . . . . . . . 11
5.5. Query ID: 16 bits . . . . . . . . . . . . . . . . . . . . 11
5.6. Client Port # . . . . . . . . . . . . . . . . . . . . . . 11
6. IPv4 Mtrace2 Standard Response Block . . . . . . . . . . . . . 12
6.1. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 12
6.2. Incoming Interface Address: 32 bits . . . . . . . . . . . 13
6.3. Outgoing Interface Address: 32 bits . . . . . . . . . . . 13
6.4. Previous-Hop Router Address: 32 bits . . . . . . . . . . . 13
6.5. Input packet count on incoming interface: 64 bits . . . . 13
6.6. Output packet count on incoming interface: 64 bits . . . . 13
6.7. Total number of packets for this source-group pair: 64
bits . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.8. Rtg Protocol: 8 bits . . . . . . . . . . . . . . . . . . . 14
6.9. Fwd TTL: 8 bits . . . . . . . . . . . . . . . . . . . . . 14
6.10. MBZ: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . 14
6.11. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.12. Src Mask: 6 bits . . . . . . . . . . . . . . . . . . . . . 14
6.13. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 14
7. IPv6 Mtrace2 Standard Response Block . . . . . . . . . . . . . 17
7.1. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 17
7.2. Incoming Interface ID: 32 bits . . . . . . . . . . . . . . 17
7.3. Outgoing Interface ID: 32 bits . . . . . . . . . . . . . . 18
7.4. Local Address . . . . . . . . . . . . . . . . . . . . . . 18
7.5. Remote Address . . . . . . . . . . . . . . . . . . . . . . 18
7.6. Input packet count on incoming interface . . . . . . . . . 18
7.7. Output packet count on incoming interface . . . . . . . . 18
7.8. Total number of packets for this source-group pair . . . . 18
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7.9. Rtg Protocol: 8 bits . . . . . . . . . . . . . . . . . . . 19
7.10. MBZ: 7 bits . . . . . . . . . . . . . . . . . . . . . . . 19
7.11. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.12. Src Prefix Len: 8 bits . . . . . . . . . . . . . . . . . . 19
7.13. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 19
8. Mtrace2 Augmented Response Block . . . . . . . . . . . . . . . 20
9. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 21
9.1. Traceroute Query . . . . . . . . . . . . . . . . . . . . . 21
9.1.1. Packet Verification . . . . . . . . . . . . . . . . . 21
9.1.2. Normal Processing . . . . . . . . . . . . . . . . . . 21
9.2. Mtrace2 Request . . . . . . . . . . . . . . . . . . . . . 21
9.2.1. Packet Verification . . . . . . . . . . . . . . . . . 22
9.2.2. Normal Processing . . . . . . . . . . . . . . . . . . 22
9.3. Forwarding Mtrace2 Requests . . . . . . . . . . . . . . . 24
9.4. Sending Mtrace2 Responses . . . . . . . . . . . . . . . . 24
9.4.1. Destination Address . . . . . . . . . . . . . . . . . 24
9.4.2. Source Address . . . . . . . . . . . . . . . . . . . . 24
9.5. Proxying Mtrace2 Queries . . . . . . . . . . . . . . . . . 24
9.6. Hiding Information . . . . . . . . . . . . . . . . . . . . 25
10. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 26
10.1. Sending Mtrace2 Queries . . . . . . . . . . . . . . . . . 26
10.2. Determining the Path . . . . . . . . . . . . . . . . . . . 26
10.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 26
10.4. Last Hop Router . . . . . . . . . . . . . . . . . . . . . 26
10.5. First Hop Router . . . . . . . . . . . . . . . . . . . . . 27
10.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 27
10.7. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 27
10.7.1. Arriving at source . . . . . . . . . . . . . . . . . . 27
10.7.2. Fatal error . . . . . . . . . . . . . . . . . . . . . 27
10.7.3. No previous hop . . . . . . . . . . . . . . . . . . . 27
10.7.4. Traceroute shorter than requested . . . . . . . . . . 28
10.8. Continuing after an error . . . . . . . . . . . . . . . . 28
11. Protocol-Specific Considerations . . . . . . . . . . . . . . . 29
11.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 29
11.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 29
11.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 29
11.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 29
11.5. AMT . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
12. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 31
12.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 31
12.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 31
12.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 31
12.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 32
12.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 32
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
13.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 33
13.2. UDP Destination Port and IPv6 Address . . . . . . . . . . 33
14. Security Considerations . . . . . . . . . . . . . . . . . . . 34
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14.1. Topology Discovery . . . . . . . . . . . . . . . . . . . . 34
14.2. Traffic Rates . . . . . . . . . . . . . . . . . . . . . . 34
14.3. Limiting Query/Request Rates . . . . . . . . . . . . . . . 34
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 35
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
16.1. Normative References . . . . . . . . . . . . . . . . . . . 36
16.2. Informative References . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38
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1. Introduction
The unicast "traceroute" program allows the tracing of a path from
one machine to another. The key mechanism for unicast traceroute is
the ICMP TTL exceeded message, which is specifically precluded as a
response to multicast packets. On the other hand, the multicast
traceroute facility allows the tracing of an IP multicast routing
paths. In this document, we specify the multicast "traceroute"
facility to be implemented in multicast routers and accessed by
diagnostic programs. The multicast traceroute described in this
document named as mtrace version 2 or mtrace2 provides additional
information about packet rates and losses that the unicast traceroute
cannot, and generally requires fewer packets to be sent.
o. To be able to trace the path that a packet would take from some
source to some destination.
o. To be able to isolate packet loss problems (e.g., congestion).
o. To be able to isolate configuration problems (e.g., TTL
threshold).
o. To minimize packets sent (e.g. no flooding, no implosion).
This document supports both IPv4 and IPv6 multicast traceroute
facility. The protocol design, concept, and program behavior are
same between IPv4 and IPv6 mtrace2. While the original IPv4
multicast traceroute, mtrace, the query and response messages are
implemented as IGMP messages [12], all mtrace2 messages are carried
on UDP. The packet formats of IPv4 and IPv6 mtrace2 are different
because of the different address families, but the syntax is similar.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT","SHOULD", "SHOULD NOT", "RECOMMENDED","MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119 [1].
Since multicast traceroutes 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 traffic is expected from the specified source
and group.
Outgoing interface:
The interface on which traffic is forwarded from the specified source
and group toward the destination. It is the interface on which the
multicast traceroute Request was received.
Previous-hop router:
The router that is on the link attached to the Incoming Interface and
is responsible for forwarding traffic for the specified source and
group.
Group state:
It is the state in which a shared-tree protocol (e.g., PIM-SM [8])
running on a router chooses the previous-hop router toward the core
router or Rendezvous Point (RP) as its parent router. In this state,
source-specific state is not available for the corresponding
multicast address on the router.
Source-specific state:
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.
ALL-[protocol]-ROUTERS.MCAST.NET:
It is a dedicated multicast address for a multicast router to
communicate with other routers that are working with the same routing
protocol. For instance,the address of ALL-PIM-ROUTERS.MCAST.NET is
'224.0.0.13' for IPv4 and 'ff02::d' for IPv6.
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3. Overview
Given a multicast distribution tree, tracing from a source to a
multicast destination is hard, since you don't know down which branch
of the multicast tree the destination lies. This means that you have
to flood the whole tree to find the path from one source to one
destination. However, walking up the tree from destination to source
is easy, as most existing multicast routing protocols know the
previous hop for each source. Tracing from destination to source can
involve only routers on the direct path.
The party requesting the traceroute sends a traceroute Query packet
to the last-hop multicast router for the given destination. The
last-hop router turns the Query into a Request packet by adding a
response data block containing its interface addresses and packet
statistics, and then forwards the Request packet via unicast to the
router that it believes is the proper previous hop for the given
source and group. Each hop adds its response data to the end of the
Request packet, then unicast forwards it to the previous hop. The
first hop router (the router that believes that packets from the
source originate on one of its directly connected networks) changes
the packet type to indicate a Response packet and sends the completed
response to the response destination address. The response may be
returned before reaching the first hop router if a fatal error
condition such as "no route" is encountered along the path.
Multicast traceroute uses any information available to it in the
router to attempt to determine a previous hop to forward the trace
towards. Multicast routing protocols vary in the type and amount of
state they keep; multicast traceroute endeavors to work with all of
them by using whatever is available. For example, if a PIM-SM router
is on the (*,G) tree, it chooses the parent towards the RP as the
previous hop. In these cases, no source/group-specific state is
available, but the path may still be traced.
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4. Packet Formats
Mtrace2 message is encoded in TLV format. If an implementation
receives a TLV whose length exceeds the TLV length specified in the
Length field, the TLV SHOULD be accepted but any additional data
SHOULD be ignored.
4.1. 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)
Length (16 bits)
Value (variable length)
4.2. Defined TLVs
The following TLV Types are defined:
Code Type
====== ======================================
1 Mtrace2 Query
2 Mtrace2 Response
3 Mtrace2 Standard Response Block
4 Mtrace2 Augmented Response Block
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
completed and sent as a response from the first hop router to the
querier. Two codes are required so that multicast routers will not
attempt to process a completed response in those cases where the
initial query was issued from a router.
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5. Mtrace2 Query Header
The mtrace2 message is carried as a UDP packet. The UDP source port
is uniquely selected by the local host operating system. The UDP
destination port is the IANA reserved mtrace2 port number (see
Section 13). The UDP checksum MUST be valid in mtrace2 messages.
The mtrace2 message includes the common mtrace2 Query header as
follows. The header is only filled in by the originator of the
mtrace2 Query; intermediate routers MUST NOT modify any of the
fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| # hops |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Multicast Address |
| |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| |
| Source Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Destination Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query ID | Client Port # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
5.1. # hops: 8 bits
This field specifies the maximum number of hops that the requester
wants to trace. If there is some error condition in the middle of
the path that keeps the mtrace2 request from reaching the first-hop
router, this field can be used to perform an expanding-ring search to
trace the path to just before the problem.
5.2. Multicast Address
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
IPv4 or with the unspecified address (::) in case of IPv6 if no
group-specific information is desired. Note that non-group-specific
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mtrace2 MUST specify source address.
5.3. Source Address
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
filled with "all 1" in case of IPv4 or with the unspecified address
(::) in case of IPv6 if no source-specific information is desired.
Note that non-source-specific traceroutes may not be possible with
certain multicast routing protocols.
5.4. Destination Address
This field specifies the 32 bits length IPv4 or 128 bits length IPv6
address of the multicast receiver for the path being traced. The
trace starts at this destination and proceeds toward the traffic
source.
5.5. Query ID: 16 bits
This field is used as a unique identifier for this traceroute request
so that duplicate or delayed responses may be detected and to
minimize collisions when a multicast response address is used.
5.6. Client Port #
Mtrace2 response is sent back to the address specified in a
Destination 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.
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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 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Incoming Interface Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outgoing Interface Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Previous-Hop Router Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Input packet count on incoming interface .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Output packet count on outgoing interface .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Total number of packets for this source-group pair .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |M| | | |
| Rtg Protocol | Fwd TTL |B|S| Src Mask |Forwarding Code|
| | |Z| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.1. Query Arrival Time: 32 bits
The Query Arrival Time is a 32-bit NTP timestamp specifying the
arrival time of the traceroute request packet at this router. The
32-bit form of an NTP timestamp consists of the middle 32 bits of the
full 64-bit form; that is, the low 16 bits of the integer part and
the high 16 bits of the fractional part.
The following formula converts from a UNIX timeval to a 32-bit NTP
timestamp:
query_arrival_time
= (tv.tv_sec + 32384) << 16 + ((tv.tv_usec << 10) / 15625)
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The constant 32384 is the number of seconds from Jan 1, 1900 to Jan
1, 1970 truncated to 16 bits. ((tv.tv_usec << 10) / 15625) is a
reduction of ((tv.tv_usec / 100000000) << 16).
6.2. Incoming Interface Address: 32 bits
This field specifies the address of the interface on which packets
from this source and group are expected to arrive, or 0 if unknown.
6.3. Outgoing Interface Address: 32 bits
This field specifies the address of the interface on which packets
from this source and group flow to the specified destination, or 0 if
unknown.
6.4. Previous-Hop Router Address: 32 bits
This field specifies the router from which this router expects
packets from this source. This may be a multicast group (e.g. ALL-
[protocol]-ROUTERS.MCAST.NET) if the previous hop is not known
because of the workings of the multicast routing protocol. However,
it should be 0 if the incoming interface address is unknown.
6.5. Input packet count on incoming interface: 64 bits
This field contains the number of multicast packets received for all
groups and sources on the incoming interface, or "all 1" if no count
can be reported. This counter may have the same value as
ifHCInMulticastPkts from the IF-MIB [14] for this interface.
6.6. Output packet count on incoming interface: 64 bits
This field contains the number of multicast packets that have been
transmitted or queued for transmission for all groups and sources on
the outgoing interface, or "all 1" if no count can be reported. This
counter may have the same value as ifHCOutMulticastPkts from the IF-
MIB for this interface.
6.7. Total number of packets for this source-group pair: 64 bits
This field counts the number of packets from the specified source
forwarded by this router to the specified group, or "all 1" if no
count can be reported. If the S bit is set, the count is for the
source network, as specified by the Src Mask field. If the S bit is
set and the Src Mask field is 63, indicating no source-specific
state, the count is for all sources sending to this group. This
counter should have the same value as ipMcastRoutePkts from the
IPMROUTE-STD-MIB [15] for this forwarding entry.
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6.8. Rtg Protocol: 8 bits
This field describes the routing protocol in use between this router
and the previous-hop router. Specified values include:
0 Unknown
1 PIM
2 PIM using special routing table
3 PIM using a static route
4 PIM using MBGP route
5 PIM using state created by Assert processing
6 Bi-directional PIM
7 IGMP/MLD proxy
8 AMT relay
9 AMT gateway
10 AMT gateway with IGMP/MLD proxy
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
This field contains the TTL that a packet is required to have before
it will be forwarded over the outgoing interface.
6.10. MBZ: 1 bit
Must be zeroed on transmission and ignored on reception.
6.11. S: 1 bit
This S bit indicates that the packet count for the source-group pair
is for the source network, as determined by masking the source
address with the Src Mask field.
6.12. Src Mask: 6 bits
This field contains the number of 1's in the netmask this router has
for the source (i.e. a value of 24 means the netmask is 0xffffff00).
If the router is forwarding solely on group state, this field is set
to 63 (0x3f).
6.13. Forwarding Code: 8 bits
This field contains a forwarding information/error code. Section 9.2
explains how and when the forwarding code is filled. Defined values
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are as follows;
Value Name Description
----- -------------- -------------------------------------------
0x00 NO_ERROR No error
0x01 WRONG_IF Mtrace2 request arrived on an interface
to which this router would not forward for
this source, group, destination.
0x02 PRUNE_SENT This router has sent a prune upstream which
applies to the source and group in the
traceroute request.
0x03 PRUNE_RCVD This router has stopped forwarding for this
source and group in response to a request
from the next hop router.
0x04 SCOPED The group is subject to administrative
scoping at this hop.
0x05 NO_ROUTE This router has no route for the source or
group and no way to determine a potential
route.
0x06 WRONG_LAST_HOP This router is not the proper last-hop
router.
0x07 NOT_FORWARDING This router is not forwarding this source,
group out the outgoing interface for an
unspecified reason.
0x08 REACHED_RP Reached Rendezvous Point or Core
0x09 RPF_IF Mtrace2 request arrived on the expected
RPF interface for this source and group.
0x0A NO_MULTICAST Mtrace2 request arrived on an interface
which is not enabled for multicast.
0x0B INFO_HIDDEN One or more hops have been hidden from this
trace.
0x0C REACHED_GW Mtrace2 request arrived on a gateway (e.g.,
a NAT or firewall) that hides the
information between this router and the
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mtrace2 querier
0x81 NO_SPACE There was not enough room to insert another
response data block in the packet.
0x82 OLD_ROUTER The previous-hop router does not understand
mtrace2 requests.
0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited.
Note that if a router discovers there is not enough room in a packet
to insert its response, it puts the NO_SPACE error code in the
previous router's Forwarding Code field, overwriting any error the
previous router placed there. After the router sends the response to
the Destination Address in the header, the router continues the
mtrace2 query by sending an mtrace2 request containing the same
mtrace2 query header. Section 9.3 and Section 10.8 include the
details.
The 0x80 bit of the Forwarding Code is used to indicate a fatal
error. A fatal error is one where the router may know the previous
hop but cannot forward the message to it.
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7. IPv6 Mtrace2 Standard Response Block
Each intermediate IPv6 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 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Incoming Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outgoing Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
* Local Address *
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
* Remote Address *
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Input packet count on incoming interface .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Output packet count on outgoing interface .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Total number of packets for this source-group pair .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rtg Protocol | MBZ |S|Src Prefix Len |Forwarding Code|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7.1. Query Arrival Time: 32 bits
Same definition described in Section 6.1
7.2. Incoming Interface ID: 32 bits
This field specifies the interface ID on which packets from this
source and group are expected to arrive, or 0 if unknown. This ID
should be the value taken from InterfaceIndex of the IF-MIB [14] for
this interface. This field is carried in network byte order.
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7.3. Outgoing Interface ID: 32 bits
This field specifies the interface ID on which packets from this
source and group flow to the specified destination, or 0 if unknown.
This ID should be the value taken from InterfaceIndex of the IF-MIB
for this interface. This field is carried in network byte order.
7.4. Local Address
This field specifies a global IPv6 address that uniquely identifies
the router. A unique local unicast address [13] 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.
7.5. Remote Address
This field specifies the address of the previous-hop router, which,
in most cases, is a link-local unicast address for the queried source
and destination addresses.
Although a link-local address does not have enough information to
identify a node, it is possible to detect the previous-hop router
with the assistance of Incoming Interface ID and the current router
address (i.e., Local Address).
This may be a multicast group (e.g., ALL-[protocol]-
ROUTERS.MCAST.NET) if the previous hop is not known because of the
workings of the multicast routing protocol. However, it should be
the unspecified address (::) if the incoming interface address is
unknown.
7.6. Input packet count on incoming interface
Same definition described in Section 6.5
7.7. Output packet count on incoming interface
Same definition described in Section 6.6
7.8. Total number of packets for this source-group pair
This field counts the number of packets from the specified source
forwarded by this router to the specified group, or "all 1" if no
count can be reported. If the S bit is set, the count is for the
source network, as specified by the Src Prefix Len field. If the S
bit is set and the Src Prefix Len field is 255, indicating no source-
specific state, the count is for all sources sending to this group.
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This counter should have the same value as ipMcastRoutePkts from the
IPMROUTE-STD-MIB for this forwarding entry.
7.9. Rtg Protocol: 8 bits
Same definition described in Section 6.8
7.10. MBZ: 7 bits
Must be zeroed on transmission and ignored on reception.
7.11. S: 1 bit
This S bit indicates that the packet count for the source-group pair
is for the source network, as determined by masking the source
address with the Src Prefix Len field.
7.12. Src Prefix Len: 8 bits
This field contains the prefix length this router has for the source.
If the router is forwarding solely on group state, this field is set
to 255 (0xff)
7.13. Forwarding Code: 8 bits
Same definition described in Section 6.13
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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
Destination 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 purposes, 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 seen in Section 4.1.
The following augmented response block type is defined:
Code Type
====== =================================================
0x01 # Mtrace2 Standard Response Blocks Returned
When the NO_SPACE error occurs, the router sends back the mtrace2
response with contained data (i.e., all appended response blocks),
and continues the mtrace2 query by sending an mtrace2 request as will
be described in Section 9.3. In this mtrace2 request, the router
appends the augmented response block with the code "0x01" and the
number of returned mtrace2 response blocks. Every router between
this router and the first-hop router can recognize the limit number
of hops by referring this number and the # hops in the header.
This document only defines the above augmented response block type
and does not define other augmented response block types. Specifing
how to deal with diagnosis information will be also described in
separate documents.
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9. Router Behavior
All of these actions are performed in addition to (NOT instead of)
forwarding the packet, if applicable. E.g. a multicast packet that
has TTL or the hop limit remaining MUST be forwarded normally, as
MUST a unicast packet that has TTL or the hop limit remaining and is
not addressed to this router.
9.1. Traceroute Query
An mtrace2 Query message is a traceroute message with no response
blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 mtrace2.
9.1.1. Packet Verification
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
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
Address and is the router that would forward traffic from the given
(S,G) onto that subnet.
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
depending if the Query was received via multicast or unicast. If the
Query was received via multicast, then it MUST be silently dropped.
If it was received via unicast, a forwarding code of WRONG_LAST_HOP
is noted and processing continues as in Section 9.2
Duplicate Query messages as identified by the tuple (IP Source, Query
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
Query message that was processed, and ignoring future messages with
the same IP Source and Query ID). Duplicate Request messages MUST
NOT be ignored in this manner.
9.1.2. Normal Processing
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
performs the steps listed in Section 9.2
9.2. Mtrace2 Request
An mtrace2 Request is a traceroute message with some number of
response blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6
mtrace2. Routers can tell the difference between Queries and
Requests by checking the length of the packet.
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9.2.1. Packet Verification
If the mtrace2 Request does not come from an adjacent host or router,
it MUST be silently ignored. If the mtrace2 Request is not addressed
to this router, or if the Request is addressed to a multicast group
which is not a link-scoped group (i.e. 224/24 for IPv4, FFx2::/16 [3]
for IPv6), it MUST be silently ignored. The router's neighbor
information, e.g. ARP database or PIM neighbor list, should be used
to determine whether the host or router is adjacent or not.
9.2.2. Normal Processing
When a router receives an mtrace2 Request, it performs the following
steps. Note that it is possible to have multiple situations covered
by the Forwarding Codes. The first one encountered is the one that
is reported, i.e. all "note forwarding code N" should be interpreted
as "if forwarding code is not already set, set forwarding code to N".
1. If there is room in the current buffer (or the router can
efficiently allocate more space to use), insert a new response
block into the packet and fill in the Query Arrival Time,
Outgoing Interface Address (for IPv4 mtrace2) or Outgoing
Interface ID (for IPv6 mtrace2), Output Packet Count, and Fwd
TTL (for IPv4 mtrace2). If there was no room, fill in the
response code "NO_SPACE" in the *previous* hop's response block,
and forward the packet to the address specified in the
Destination Address field and continue the trace as described in
Section 9.3.
2. Attempt to determine the forwarding information for the source
and group specified, using the same mechanisms as would be used
when a packet is received from the source destined for the
group. State need not be instantiated, it can be "phantom"
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
state, or if no source-specific information is desired (i.e.,
"all 1" for IPv4 or unspecified address (::) for IPv6), group
state should be used. If there is no group state or no group-
specific information is desired, potential source state (i.e.
the path that would be followed for a source-specific Join)
should be used. If this router is the Core or RP and no source-
specific state is available (e.g., this router has been
receiving PIM Register messages from the first-hop router), note
a code of REACHED_RP.
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3. If no forwarding information can be determined, the router notes
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
the requester as described in Section 9.3.
4. Fill in the Incoming Interface Address, Previous-Hop Router
Address, Input Packet Count, Total Number of Packets, Routing
Protocol, S, and Src Mask from the forwarding information that
was determined.
5. If mtrace2 is administratively prohibited or the previous hop
router does not understand mtrace2 requests, note the
appropriate forwarding code (ADMIN_PROHIB or OLD_ROUTER). If
mtrace2 is administratively prohibited and any of the fields as
filled in step 4 are considered private information, zero out
the applicable fields. Then the packet is forwarded to the
requester as described in Section 9.3.
6. If the reception interface is not enabled for multicast, note
forwarding code NO_MULTICAST. If the reception interface is the
interface from which the router would expect data to arrive from
the source, note forwarding code RPF_IF. Otherwise, if the
reception interface is not one to which the router would forward
data from the source to the group, a forwarding code of WRONG_IF
is noted.
7. If the group is subject to administrative scoping on either the
Outgoing or Incoming interfaces, a forwarding code of SCOPED is
noted.
8. If this router is the Rendezvous Point or Core for the group, a
forwarding code of REACHED_RP is noted.
9. If this router has sent a prune upstream which applies to the
source and group in the mtrace2 Request, it notes forwarding
code PRUNE_SENT. If the router has stopped forwarding
downstream in response to a prune sent by the next hop router,
it notes forwarding code PRUNE_RCVD. If the router should
normally forward traffic for this source and group downstream
but is not, it notes forwarding code NOT_FORWARDING.
10. If this router is a gateway (e.g., a NAT or firewall) that hides
the information between this router and the mtrace2 querier, it
notes forwarding code REACHED_GW.
11. The packet is then sent on to the previous hop or the
Destination Address as described in Section 9.3.
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9.3. Forwarding Mtrace2 Requests
If the Previous-hop router is known for this request and the number
of response blocks is less than the number requested (i.e., the "#
hops" field in mtrace2 header), the packet is sent to that router.
If the Incoming Interface is known but the Previous-hop router is not
known, the packet is sent to an appropriate multicast address on the
Incoming Interface. The appropriate multicast address may depend on
the routing protocol in use, MUST be a link-scoped group (i.e. 224/24
for IPv4, FF02::/16 for IPv6), MUST NOT be ALL-SYSTEMS.MCAST.NET
(224.0.0.1) for IPv4 and All Nodes Address (FF02::1) for IPv6, and
MAY be ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers
Address (FF02::2) for IPv6 if the routing protocol in use does not
define a more appropriate group. Otherwise, it is sent to the
Destination Address in the header.
When the REACHED_GW code is noted, the router sends back the mtrace2
response as in Section 9.4. In addition to that, it must continue
the mtrace2 query by proxying the original querier as in Section 9.5.
When the NO_SPACE error occurs, the router sends back the mtrace2
response with contained data and the NO_SPACE error code as in
Section 9.4, and continues the mtrace2 query by sending an mtrace2
request containing the same mtrace2 query header and its standard and
augmented response blocks. The corresponding augmented response
block type is "# Mtrace2 Response Blocks Returned" described in
Section 8.
9.4. Sending Mtrace2 Responses
9.4.1. Destination Address
An mtrace2 Response must be sent to the address specified in the
Destination Address field in the mtrace2 query header.
9.4.2. Source Address
An mtrace2 Response must be sent with the address of the router's
reception interface.
9.5. Proxying Mtrace2 Queries
When a gateway (e.g., a NAT or firewall) that needs to block unicast
packets to the mtrace2 querier or hide information between the
gateway and the mtrace2 querier receives mtrace2 query from an
adjacent host or mtrace2 request from an adjacent router, it sends
back the mtrace2 response with contained data and the REACHED_GW code
to the address specified in the Destination Address field in the
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mtrace2 query header.
At the same time, the gateway prepares a new mtrace2 query message.
The gateway uses the original mtrace2 query header as the base for
the new mtrace2 query; it sets the Destination Address to its
Incoming Interface address and the Client Port # to its own port
(which may be the same as the mtrace2 port as the gateway is
listening on that port), and decreases # hops according to the number
of standard response blocks in the returned mtrace2 response from the
gateway. The mtrace2 query message is sent to the previous-hop
router or to an appropriate multicast address on the Incoming
Interface.
When the gateway receives the mtrace2 response from the first-hop
router or any intermediate router, it MUST forward the mtrace2
response back to the mtrace2 querier with the original mtrace2 query
header.
9.6. Hiding Information
Information about a domain's topology and connectivity may be hidden
from multicast traceroute requests. The INFO_HIDDEN forwarding code
may be used to note that, for example, the incoming interface address
and packet count are for the entrance to the domain and the outgoing
interface address and packet count are the exit from the domain. The
source-group packet count may be from either router or not specified
(all 1).
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10. Client Behavior
10.1. Sending Mtrace2 Queries
When the destination of the mtrace2 is the machine running the
client, the mtrace2 Query packet can be sent to the ALL-
ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers Address
(FF02::2) for IPv6. This will ensure that the packet is received by
the last-hop router on the subnet. Otherwise, if the proper last-hop
router is known for the mtrace2 destination, the Query could be
unicasted to that router.
See also Section 10.4 on determining the last-hop router.
10.2. Determining the Path
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
this attempt fails, one strategy is to perform a linear search (as
the traditional unicast traceroute program does); set the "# hops"
field to 1 and try to get a response, then 2, and so on. If no
response is received at a certain hop, the hop count can continue
past the non-responding hop, in the hopes that further hops may
respond. These attempts should continue until a user-defined timeout
has occurred.
See also Section 10.5 and Section 10.6 on receiving the results of a
trace.
10.3. Collecting Statistics
After a client has determined that it has traced the whole path or as
much as it can expect to (see Section 10.7), it might collect
statistics by waiting a short time and performing a second trace. If
the path is the same in the two traces, statistics can be displayed
as described in Section 12.3 and Section 12.4.
10.4. Last Hop Router
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
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
Routers Address (FF02::2) for IPv6. All routers except the correct
last hop router should ignore any mtrace2 request received via
multicast. Mtrace2 requests which are multicasted to the group being
traced must include the Router Alert option[6][7].
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Another alternative is to unicast to the trace destination. Mtrace2
requests which are unicasted to the trace destination must include
the Router Alert option, in order that the last-hop router is aware
of the packet.
10.5. First Hop Router
The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default
multicast group for IPv4 mtrace responses, in order to support mtrace
queriers that are not unicast reachable from the first hop router.
However, mtrace2 does not reserve any IPv4/IPv6 multicast addresses
for mtrace2 responses. Every mtrace2 response is sent to the unicast
address specified in the Destination Address field of the mtrace2
query header.
10.6. Broken Intermediate Router
A broken intermediate router might simply not understand mtrace2
packets, and drop them. The querier would then get no response at
all from its mtrace2 requests. It should then perform a hop-by-hop
search by setting the number of responses field until it gets a
response (both linear and binary search are options, but binary is
likely to be slower because a failure requires waiting for a
timeout).
10.7. Mtrace2 Termination
When performing an expanding hop-by-hop trace, it is necessary to
determine when to stop expanding.
10.7.1. Arriving at source
A trace can be determined to have arrived at the source if the
Incoming Interface of the last router in the trace is non-zero, but
the Previous Hop router is zero.
10.7.2. Fatal error
A trace has encountered a fatal error if the last Forwarding Error in
the trace has the 0x80 bit set.
10.7.3. No previous hop
A trace can not continue if the last Previous Hop in the trace is set
to 0.
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10.7.4. Traceroute shorter than requested
If the trace that is returned is shorter than requested (i.e. the
number of response blocks is smaller than the "# hops" field), the
trace encountered an error and could not continue.
10.8. Continuing after an error
When the NO_SPACE error occurs, as described in Section 9.3, the
multicast routers sends back the mtrace2 response to the address
specified in the Destination Address field in the mtrace2 query
header. In this case, the mtrace2 client may receive multiple
mtrace2 responses from different routers (along the path). After the
client receives multiple mtrace2 response messages, it integrates
(i.e. constructs) them as a single mtrace2 response message.
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
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
determine (via mrinfo or SNMP [13][15]) 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 a
previous-hop 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.
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11. Protocol-Specific Considerations
11.1. PIM-SM
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
source-specific join so there is no more state to trace. However,
the path that traffic would use if the RP did perform a source-
specific join can be traced by setting the trace destination to the
RP, the trace source to the traffic source, and the trace group to 0.
This trace Query may be unicasted to the RP.
11.2. Bi-Directional PIM
Bi-directional PIM [9] 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 sources to the RPA (Rendezvous Point Address) and from
the RPA to receivers without requiring source-specific state. In
contrast to PIM-SM, RP always has the state to trace.
A Designated Forwarder (DF) for a given RPA is in charge of
forwarding downstream traffic onto its link, and forwarding upstream
traffic from its link towards the RPL (Rendezvous Point Link) that
the RPA belongs to. Hence mtrace2 reports DF addresses or RPA along
the path.
11.3. PIM-DM
Routers running PIM Dense Mode do not know the path packets would
take unless traffic is flowing. Without some extra protocol
mechanism, this means that in an environment with multiple possible
paths with branch points on shared media, multicast traceroute can
only trace existing paths, not potential paths. When there are
multiple possible paths but the branch points are not on shared
media, the previous hop router is known, but the last hop router may
not know that it is the appropriate last hop.
When traffic is flowing, PIM Dense Mode routers know whether or not
they are the last-hop forwarder for the link (because they won or
lost an Assert battle) and know who the previous hop is (because it
won an Assert battle). Therefore, multicast traceroute is always
able to follow the proper path when traffic is flowing.
11.4. IGMP/MLD Proxy
When a mtrace2 Query packet reaches an incoming interface of IGMP/MLD
Proxy [10], it put a WRONG_IF (0x01) value in Forwarding Code of
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mtrace2 standard response block (as in Section 6.13) and sends the
mtrace2 response back to the Destination 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.
11.5. AMT
AMT [11] provides the multicast connectivity to the unicast-only
inter-network. To do this, multicast packets being sent to or from a
site are encapsulated in unicast packets. When a mtrace2 query
packet reaches an AMT pseudo-interface of an AMT gateway, the AMT
gateway encapsulats it to a particular AMT relay reachable across the
unicast-only infrastructure. Then the AMT relay decapsulates the
mtrace2 query packet and forwards the mtrace2 request to the
appropriate multicast router.
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12. Problem Diagnosis
12.1. Forwarding Inconsistencies
The forwarding error code can tell if a group is unexpectedly pruned
or administratively scoped.
12.2. TTL or Hop Limit Problems
By taking the maximum of hops (from source + forwarding TTL (or hop
limit) threshold) over all hops, it is possible to discover the TTL
or hop limit required for the source to reach the destination.
12.3. Packet Loss
By taking two traces, it is possible to find packet loss information
by comparing the difference in input packet counts to the difference
in output packet counts for the specified source-group address pair
at the previous hop. On a point-to-point link, any difference in
these numbers implies packet loss. Since the packet counts may be
changing as the mtrace2 query is propagating, there may be small
errors (off by 1 or 2 or more) in these statistics. However, these
errors will not accumulate if multiple traces are taken to expand the
measurement period. On a shared link, the count of input packets can
be larger than the number of output packets at the previous hop, due
to other routers or hosts on the link injecting packets. This
appears as "negative loss" which may mask real packet loss.
In addition to the counts of input and output packets for all
multicast traffic on the interfaces, the response data includes a
count of the packets forwarded by a node for the specified source-
group pair. Taking the difference in this count between two traces
and then comparing those differences between two hops gives a measure
of packet loss just for traffic from the specified source to the
specified receiver via the specified group. This measure is not
affected by shared links.
On a point-to-point link that is a multicast tunnel, packet loss is
usually due to congestion in unicast routers along the path of that
tunnel. On native multicast links, loss is more likely in the output
queue of one hop, perhaps due to priority dropping, or in the input
queue at the next hop. The counters in the response data do not
allow these cases to be distinguished. Differences in packet counts
between the incoming and outgoing interfaces on one node cannot
generally be used to measure queue overflow in the node.
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12.4. Link Utilization
Again, with two traces, you can divide the difference in the input or
output packet counts at some hop by the difference in time stamps
from the same hop to obtain the packet rate over the link. If the
average packet size is known, then the link utilization can also be
estimated to see whether packet loss may be due to the rate limit or
the physical capacity on a particular link being exceeded.
12.5. Time Delay
If the routers have synchronized clocks, it is possible to estimate
propagation and queuing delay from the differences between the
timestamps at successive hops. However, this delay includes control
processing overhead, so is not necessarily indicative of the delay
that data traffic would experience.
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13. IANA Considerations
The following new assignments can only be made via a Standards Action
as specified in [4].
13.1. Forwarding Codes
New Forwarding codes must only be created by an RFC that modifies
this document's Section 10, 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.
13.2. UDP Destination Port and IPv6 Address
The IANA should allocate UDP destination port for multicast
traceroute version 2 upon publication of the first RFC.
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14. Security Considerations
14.1. 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.
14.2. Traffic Rates
Mtrace2 can be used to discover what sources are sending to what
groups and at what rates. If this information is a secret, mtrace2
may be restricted at the border of your domain, using the
ADMIN_PROHIB forwarding code.
14.3. Limiting Query/Request Rates
Routers should limit mtrace2 queries and requests by ignoring the
received messages. Routers MAY randomly ignore the received messages
to minimize the processing overhead, i.e., to keep fairness in
processing queries.
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15. Acknowledgements
This specification started largely as a transcription of Van
Jacobson's slides from the 30th IETF, and the implementation in
mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve
Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original
multicast traceroute client, mtrace (version 1), has been implemented
by Ajit Thyagarajan, Steve Casner and Bill Fenner.
The idea of unicasting a multicast traceroute Query to the
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
subnet is due to Tom Pusateri.
For the mtrace version 2 specification, extensive comments were
received from Yiqun Cai, Liu Hui, Bharat Joshi, Shinsuke Suzuki,
Achmad Husni Thamrin, and Cao Wei.
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16. References
16.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", RFC 2119, March 1997.
[2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[3] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[4] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 2434, October 1998.
[5] Braden, B., Borman, D., and C. Partridge, "Computing the
Internet Checksum", RFC 1071, September 1988.
[6] Katz, D., "IP Router Alert Option", RFC 2113, February 1997.
[7] Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
RFC 2711, October 1999.
[8] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[9] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-PIM)",
RFC 5015, October 2007.
[10] 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] Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T.
Pusateri, "Automatic IP Multicast Without Explicit Tunnels
(AMT)", draft-ietf-mboned-auto-multicast-08.txt (work in
progress), October 2007.
16.2. Informative References
[12] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version 3",
RFC 3376, October 2002.
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[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.
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Authors' Addresses
Hitoshi Asaeda
Keio University
Graduate School of Media and Governance
Fujisawa, Kanagawa 252-8520
Japan
Email: asaeda@wide.ad.jp
URI: http://www.sfc.wide.ad.jp/~asaeda/
Tatuya Jinmei
Internet Systems Consortium
Redwood City, CA 94063
US
Email: Jinmei_Tatuya@isc.org
William C. Fenner
Arastra, Inc.
Menlo Park, CA 94025
US
Email: fenner@fenron.com
Stephen L. Casner
Packet Design, Inc.
Palo Alto, CA 94304
US
Email: casner@packetdesign.com
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