draft-ietf-idmr-traceroute-ipm-06.txt   draft-ietf-idmr-traceroute-ipm-07.txt 
Internet Engineering Task Force Inter-Domain Multicast Routing Working Group Internet Engineering Task Force Inter-Domain Multicast Routing Working Group
INTERNET-DRAFT W. Fenner INTERNET-DRAFT W. Fenner
draft-ietf-idmr-traceroute-ipm-06.txt AT&T Research draft-ietf-idmr-traceroute-ipm-07.txt AT&T Research
S. Casner S. Casner
Cisco Systems Cisco Systems
March 10, 2000 July 14, 2000
Expires August 2000 Expires January 2001
A "traceroute" facility for IP Multicast. A "traceroute" facility for IP Multicast.
Status of this Memo Status of this Memo
This document is an Internet Draft and is in full conformance with all This document is an Internet Draft and is in full conformance with all
provisions of Section 10 of RFC2026. Internet Drafts are working docu- provisions of Section 10 of RFC2026. Internet Drafts are working docu-
ments of the Internet Engineering Task Force (IETF), its areas, and its ments of the Internet Engineering Task Force (IETF), its areas, and its
working groups. Note that other groups may also distribute working doc- working groups. Note that other groups may also distribute working doc-
uments as Internet-Drafts. uments as Internet-Drafts.
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5.3. Outgoing Interface Address 5.3. Outgoing Interface Address
This field specifies the address of the interface on which packets This field specifies the address of the interface on which packets
from this source and group flow to the specified destination, or 0 from this source and group flow to the specified destination, or 0
if unknown. if unknown.
5.4. Previous-Hop Router Address 5.4. Previous-Hop Router Address
This field specifies the router from which this router expects This field specifies the router from which this router expects
packets from this source. This may be a multicast group if the packets from this source. This may be a multicast group (e.g.
previous hop is not known because of the workings of the multicast ALL-[protocol]-ROUTERS.MCAST.NET) if the previous hop is not known
routing protocol. However, it should be 0 if the incoming inter- because of the workings of the multicast routing protocol. How-
face address is unknown. ever, it should be 0 if the incoming interface address is unknown.
5.5. Packet counts 5.5. Packet counts
Note that these packet counts SHOULD be as up to date as possible. Note that these packet counts SHOULD be as up to date as possible.
If packet counts are not being maintained on the processor that If packet counts are not being maintained on the processor that
handles the traceroute request in a multi-processor router archi- handles the traceroute request in a multi-processor router archi-
tecture, the packet SHOULD be delayed while the counters are gath- tecture, the packet SHOULD be delayed while the counters are gath-
ered from the remote processor(s). If this occurs, the Query ered from the remote processor(s). If this occurs, the Query
Arrival Time should be updated to reflect the time at which the Arrival Time should be updated to reflect the time at which the
packet counts were learned. packet counts were learned.
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bit is set and the Src Mask field is 63, indicating no source-spe- bit is set and the Src Mask field is 63, indicating no source-spe-
cific state, the count is for all sources sending to this group. cific state, the count is for all sources sending to this group.
This counter should have the same value as ipMRoutePkts from the This counter should have the same value as ipMRoutePkts from the
IPMROUTE-STD-MIB for this forwarding entry. IPMROUTE-STD-MIB for this forwarding entry.
5.9. Rtg Protocol: 8 bits 5.9. Rtg Protocol: 8 bits
This field describes the routing protocol in use between this This field describes the routing protocol in use between this
router and the previous-hop router. Specified values include: router and the previous-hop router. Specified values include:
l l. 1 DVMRP 2 MOSPF 3 PIM 4 CBT 5 PIM using spe- 1 DVMRP
cial routing table 6 PIM using a static route 7 DVMRP using a 2 MOSPF
static route 8 PIM using MBGP (aka BGP4+) route 9 CBT using 3 PIM
special routing table 10 CBT using a static route 11 PIM using 4 CBT
state created by Assert processing 5 PIM using special routing table
6 PIM using a static route
7 DVMRP using a static route
8 PIM using MBGP (aka BGP4+) route
9 CBT using special routing table
10 CBT using a static route
11 PIM using state created by Assert processing
5.10. FwdTTL: 8 bits 5.10. FwdTTL: 8 bits
This field contains the TTL that a packet is required to have This field contains the TTL that a packet is required to have
before it will be forwarded over the outgoing interface. before it will be forwarded over the outgoing interface.
5.11. MBZ: 1 bit 5.11. MBZ: 1 bit
Must be zeroed on transmission and ignored on reception. Must be zeroed on transmission and ignored on reception.
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This field contains the number of 1's in the netmask this router 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 has for the source (i.e. a value of 24 means the netmask is
0xffffff00). If the router is forwarding solely on group state, 0xffffff00). If the router is forwarding solely on group state,
this field is set to 63 (0x3f). this field is set to 63 (0x3f).
5.14. Forwarding Code: 8 bits 5.14. Forwarding Code: 8 bits
This field contains a forwarding information/error code. Defined This field contains a forwarding information/error code. Defined
values include: values include:
expand; l l lw(3i) . Value Name Description _ Value Name Description
0x00 NO_ERROR No error 0x01 WRONG_IF T{ Traceroute request --------------------------------------------------------------------
arrived on an interface to which this router would not forward for 0x00 NO_ERROR No error
this source,group,destination. T} 0x02 PRUNE_SENT T{ This 0x01 WRONG_IF Traceroute request arrived on an interface to
router has sent a prune upstream which applies to the source and which this router would not forward for this
group in the traceroute request. T} 0x03 PRUNE_RCVD T{ This source,group,destination.
router has stopped forwarding for this source and group in response 0x02 PRUNE_SENT This router has sent a prune upstream which
to a request from the next hop router. T} 0x04 SCOPED T{ The applies to the source and group in the tracer-
group is subject to administrative scoping at this hop. T} oute request.
0x05 NO_ROUTE T{ This router has no route for the source or group 0x03 PRUNE_RCVD This router has stopped forwarding for this
and no way to determine a potential route. T} 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. 0x06 WRONG_LAST_HOP This router is not the proper last-hop router.
0x07 NOT_FORWARDING T{ This router is not forwarding this 0x07 NOT_FORWARDING This router is not forwarding this
source,group out the outgoing interface for an unspecified reason. source,group out the outgoing interface for an
T} 0x08 REACHED_RP Reached Rendez-vous Point or Core unspecified reason.
0x09 RPF_IF T{ Traceroute request arrived on the expected RPF 0x08 REACHED_RP Reached Rendez-vous Point or Core
interface for this source,group. T} 0x0A NO_MULTICAST T{ Tracer- 0x09 RPF_IF Traceroute request arrived on the expected RPF
oute request arrived on an interface which is not enabled for mul- interface for this source,group.
ticast. T} 0x0B INFO_HIDDEN T{ One or more hops have been hid- 0x0A NO_MULTICAST Traceroute request arrived on an interface
den from this trace. T} 0x81 NO_SPACE T{ There was not enough which is not enabled for multicast.
room to insert another response data block in the packet. T} 0x0B INFO_HIDDEN One or more hops have been hidden from this
0x82 OLD_ROUTER T{ The previous hop router does not understand trace.
traceroute requests. T} 0x83 ADMIN_PROHIB Traceroute is adminis- 0x81 NO_SPACE There was not enough room to insert another
tratively prohibited. response data block in the packet.
0x82 OLD_ROUTER The previous hop router does not understand
traceroute requests.
0x83 ADMIN_PROHIB Traceroute is administratively prohibited.
Note that if a router discovers there is not enough room in a 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 packet 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 previous router placed there. A multicast traceroute client, upon
receiving this error, MAY restart the trace at the last hop listed receiving this error, MAY restart the trace at the last hop listed
in the packet. in the packet.
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
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Details of performing a multicast traceroute: Details of performing a multicast traceroute:
7.2. Last hop router 7.2. Last hop router
The traceroute querier may not know which is the last hop router, The traceroute querier may not know which is the last hop router,
or that router may be behind a firewall that blocks unicast packets or that router may be behind a firewall that blocks unicast packets
but passes multicast packets. In these cases, the traceroute but passes multicast packets. In these cases, the traceroute
request should be multicasted to the group being traced (since the request should be multicasted to the group being traced (since the
last hop router listens to that group). All routers except the last hop router listens to that group). All routers except the
correct last hop router should ignore any multicast traceroute correct last hop router should ignore any multicast traceroute
request received via multicast. Traceroute requests which are request received via multicast. Traceroute requests which are mul-
multicasted to the group being traced must include the Router Alert ticasted to the group being traced must include the Router Alert IP
IP option [Katz97]. option [Katz97].
Another alternative is to unicast to the trace destination. Another alternative is to unicast to the trace destination.
Traceroute requests which are unicasted to the trace destination Traceroute requests which are unicasted to the trace destination
must include the Router Alert IP option [Katz97], in order that the must include the Router Alert IP option [Katz97], in order that the
last-hop router is aware of the packet. last-hop router is aware of the packet.
If the traceroute querier is attached to the same router as the If the traceroute querier is attached to the same router as the
destination of the request, the traceroute request may be multicas- destination of the request, the traceroute request may be multicas-
ted to 224.0.0.2 (ALL-ROUTERS.MCAST.NET) if the last-hop router is ted to 224.0.0.2 (ALL-ROUTERS.MCAST.NET) if the last-hop router is
not known. not known.
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the trace by starting it at the last hop in the trace. It can do the trace by starting it at the last hop in the trace. It can do
this by unicasting to this router's outgoing interface address, this by unicasting to this router's outgoing interface address,
keeping all fields the same. If this results in a single hop and a keeping all fields the same. If this results in a single hop and a
"WRONG_IF" error, the client may try setting the trace destination "WRONG_IF" error, the client may try setting the trace destination
to the same outgoing interface address. to the same 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 router's address will be in the Previous Hop field of the last
entry in the last reply packet received. A client may be able to entry in the last reply packet received. A client may be able to
determine (via mrinfo[Pusa99] or SNMP[Thal99a,Thal99b]) a list of determine (via mrinfo[Pusa99] or SNMP[Thal99,Thal00]) a list of
neighbors of the non-responding router. If desired, each of those neighbors of the non-responding router. If desired, each of those
neighbors could be probed to determine the remainder of the path. neighbors could be probed to determine the remainder of the path.
Unfortunately, this heuristic may end up with multiple paths, since Unfortunately, this heuristic may end up with multiple paths, since
there is no way of knowing what the non-responding router's algo- there is no way of knowing what the non-responding router's algo-
rithm for choosing a previous-hop router is. However, if all paths rithm for choosing a previous-hop router is. However, if all paths
but one flow back towards the non-responding router, it is possible but one flow back towards the non-responding router, it is possible
to be sure that this is the correct path. to be sure that this is the correct path.
7.7. Multicast Traceroute and shared-tree routing protocols 7.7. Multicast Traceroute and shared-tree routing protocols
When using shared-tree routing protocols like PIM-SM and CBT, a When using shared-tree routing protocols like PIM-SM and CBT, a
more advanced client may use multicast traceroute to determine more advanced client may use multicast traceroute to determine
paths or potential paths. paths or potential paths.
7.7.1. PIM-SM 7.7.1. PIM-SM
When a multicast traceroute reaches a PIM-SM RP and the RP does not for- When a multicast traceroute reaches a PIM-SM RP and the RP does not
ward the trace on, it means that the RP has not performed a source- 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,
specific join so there is no more state to trace. However, the path the path that traffic would use if the RP did perform a source-spe-
that traffic would use if the RP did perform a source-specific join can cific join can be traced by setting the trace destination to the
be traced by setting the trace destination to the RP, the trace source RP, the trace source to the traffic source, and the trace group to
to the traffic source, and the trace group to 0. This trace Query may 0. This trace Query may be unicasted to the RP.
be unicasted to the RP.
7.7.2. CBT 7.7.2. CBT
When a multicast traceroute reaches a CBT Core, it must simply stop When a multicast traceroute reaches a CBT Core, it must simply stop
since CBT does not have source-specific state. However, a second trace since CBT does not have source-specific state. However, a second
can be performed, setting the trace destination to the traffic source, trace can be performed, setting the trace destination to the traf-
the trace group to the group being traced, and the trace source to the fic source, the trace group to the group being traced, and the
Core (or to 0, since CBT does not have source-specific state). This trace source to the Core (or to 0, since CBT does not have source-
trace Query may be unicasted to the Core. There are two possibilities specific state). This trace Query may be unicasted to the Core.
when combining the two traces: There are two possibilities when combining the two traces:
7.7.2.1. No overlap 7.7.2.1. No overlap
If there is no overlap between the two traces, the second trace can If there is no overlap between the two traces, the second trace can
be reversed and appended to the first trace. This composite trace be reversed and appended to the first trace. This composite trace
shows the full path from the source to the destination. shows the full path from the source to the destination.
7.7.2.2. Overlapping paths 7.7.2.2. Overlapping paths
If there is a portion of the path that is common to the ends of the If there is a portion of the path that is common to the ends of the
two traces, that portion is removed from both traces. Then, as in two traces, that portion is removed from both traces. Then, as in
the no overlap case, the second trace is reversed and appended to the no overlap case, the second trace is reversed and appended to
the first trace, and the composite trace again contains the full the first trace, and the composite trace again contains the full
path. path.
This algorithm works whether the source has joined the CBT tree or not. This algorithm works whether the source has joined the CBT tree or
not.
7.8. Protocol-specific considerations 7.8. Protocol-specific considerations
7.8.1. DVMRP 7.8.1. DVMRP
DVMRP's dominant router election and route exchange guarantees that DVMRP's dominant router election and route exchange guarantees that
DVMRP routers know whether or not they are the last-hop forwarder DVMRP routers know whether or not they are the last-hop forwarder
for the link and who the previous hop is. for the link and who the previous hop is.
7.8.2. PIM Dense Mode 7.8.2. PIM Dense Mode
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In releases up through 3.5/3.6, packets were not counted as input on an In releases up through 3.5/3.6, packets were not counted as input on an
interface if the reverse-path forwarding check decided that the packets interface if the reverse-path forwarding check decided that the packets
should be dropped. That causes the packets to appear as lost on the should be dropped. That causes the packets to appear as lost on the
link if they were output by the upstream hop. This situation can arise link if they were output by the upstream hop. This situation can arise
when two routers on the path for the group being traced are connected by when two routers on the path for the group being traced are connected by
a shared link, and the path for some other group does not flow between a shared link, and the path for some other group does not flow between
those two routers because the downstream router receives packets for the those two routers because the downstream router receives packets for the
other group on another interface, but the upstream router is the elected other group on another interface, but the upstream router is the elected
forwarder to other routers or hosts on the shared link. forwarder to other routers or hosts on the shared link.
The packet counts for source/group pairs are generally kept in router
forwarding caches. These cache entries may be occasionally garbage-col-
lected on routers, so a multicast traceroute client should be prepared
to see packet counts decrease. If a long-running traceroute is keeping
a "base" to compare against, it should use the post-reset trace as the
new "base", as previous values returned by this hop are no longer valid.
In addition, it may choose to discard the data for all other hops to
cover the same amount of time for all hops.
Some routers (notably the obsolete mrouted 3.3 and 3.4) can constantly
reset these packet counts. A client might want to detect routers that
are constantly resetting and simply fail to collect statistics for that
hop (instead of allowing it to cause all other data to be discarded).
Some routers send byte-swapped counter values. If the difference
between a pair of measurements is extremely large, a traceroute client
may want to see if the difference is more reasonable when byte-swapped.
Note that this heuristic may start misfiring when packet rates get high,
so implementations may want to only attempt this heuristic when the
packet rate is much different on one router than on surrounding routers.
Some implementations (e.g. UNIX mrouted 3.8 and before) return incorrect
time values; the difference between the time values for the same hop in
two traces may have no relationship with the amount of time that passed
between making the traces. Implementations should check that time val-
ues look valid before using them.
10. Acknowledgments 10. Acknowledgments
This specification started largely as a transcription of Van Jacobson's 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 slides from the 30th IETF, and the implementation in mrouted 3.3 by Ajit
Thyagarajan. Van's original slides credit Steve Casner, Steve Deering, Thyagarajan. Van's original slides credit Steve Casner, Steve Deering,
Dino Farinacci and Deb Agrawal. A multicast traceroute client, mtrace, Dino Farinacci and Deb Agrawal. A multicast traceroute client, mtrace,
has been implemented by Ajit Thyagarajan, Steve Casner and Bill Fenner. has been implemented by Ajit Thyagarajan, Steve Casner and Bill Fenner.
The idea of unicasting a multicast traceroute Query to the destination 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 trace with Router Alert set is due to Tony Ballardie. The idea
skipping to change at page 21, line 39 skipping to change at page 22, line 39
Brad88 Braden, B., D. Borman, C. Partridge, "Computing the Brad88 Braden, B., D. Borman, C. Partridge, "Computing the
Internet Checksum", RFC 1071, ISI, September 1988. Internet Checksum", RFC 1071, ISI, September 1988.
Brad97 Bradner, S., "Key words for use in RFCs to Indicate Brad97 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119/BCP 14, Harvard University, Requirement Levels", RFC 2119/BCP 14, Harvard University,
March 1997. March 1997.
Katz97 Katz, D., "IP Router Alert Option," RFC 2113, Cisco Sys- Katz97 Katz, D., "IP Router Alert Option," RFC 2113, Cisco Sys-
tems, February 1997. tems, February 1997.
Pusa99 Pusateri, T., "DVMRP Version 3", work in progress, June Pusa99 Pusateri, T., "DVMRP Version 3", work in progress,
1999. September 1999.
Thal99a Thaler, D., "PIM MIB", work in progress, June 1999. Thal00 Thaler, D., "PIM MIB", work in progress, July 2000.
Thal99b Thaler, D., "DVMRP MIB", work in progress, May 1998. Thal99 Thaler, D., "DVMRP MIB", work in progress, October 1999.
14. Authors' Addresses 14. Authors' Addresses
William C. Fenner William C. Fenner
AT&T Labs -- Research AT&T Labs -- Research
75 Willow Rd. 75 Willow Rd.
Menlo Park, CA 94025 Menlo Park, CA 94025
United States United States
Email: fenner@research.att.com Email: fenner@research.att.com
Stephen L. Casner Stephen L. Casner
Cisco Systems, Inc. Cisco Systems, Inc.
170 West Tasman Drive 170 West Tasman Drive
San Jose, CA 95134 San Jose, CA 95134
United States United States
Email: casner@cisco.com Email: casner@cisco.com
15. Changes from the last revision: 15. Change History
(To be removed before publication as RFC)
15.1. Changes from draft-ietf-idmr-traceroute-ipm-06.txt:
- Added implementation-specific notes as suggested by Dave Thaler:
- Forwarding cache entries going away while traffic is flowing,
causing reset counters.
- mrouted 3.3 and 3.4 constant resets
- byte-swapped counters
- bogus time due to missed ntohl() parenthesis in mrouted <= 3.8
- Add example of ALL-[protocol]-ROUTERS.MCAST.NET for the multicast-
on-prev-hop. (Maybe this isn't important any more; PIM used to be
allowed to not know the proper prev hop but that's not true any
more)
15.2. Changes from draft-ietf-idmr-traceroute-ipm-05.txt:
- Changes section added. - Changes section added.
- Updated abstract - Updated abstract
- Added mention of up-to-date packet counts, in particular allowing - Added mention of up-to-date packet counts, in particular allowing
the delay of an mtrace packet while the counts are fetched in a the delay of an mtrace packet while the counts are fetched in a
distributed architecture. distributed architecture.
- Added mention of ifInMulticastPkts, ifOutMulticastPkts, and ipM- - Added mention of ifInMulticastPkts, ifOutMulticastPkts, and ipM-
 End of changes. 

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