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Investigating Multicast Routes
You can use the mtrace command to trace the path that multicast packets take from a source
to a destination through a multicast group address. This command is
similar to the traceroute command for investigating
unicast routes.
mtrace
- Use to trace the path that multicast packets take to
a destination.
- Specify the unicast IP address of the source for the packets.
- To direct the packets to a particular destination, specify
the unicast address for that destination. If you do not specify a
destination, the router traces the route from the device on which
you issue the command.
- To direct the packets through a particular multicast group
address, specify that multicast group address. If you do not specify
a multicast group address, the router traces the route through the
MBone audio multicast group.
- To send the trace to a particular device, specify the
IP address of that device. If you do not specify a response address,
the router sends the trace to an IP address on the router.
- To investigate a problem at a particular point in the
route, specify the maximum number of hops for the trace. The default
number of hops is 64.
- The trace starts at the destination and works back to
the source.
- Field descriptions
- Tracing multicast route from a.a.a.a to b.b.b.b for group c.c.c.c using response address d.d.d.d—A description
of the trace is as follows:
-
a.a.a.a—IP address of the
source
-
b.b.b.b—IP address of the
destination
-
c.c.c.c—IP address of the
multicast group
-
d.d.d.d—IP address of the
router to which the router sends the trace
- Received mtrace response packet of length n—Length of the response packet, in bytes
- Each line of the trace has the following format: hops. ip-address Protocol: protocol FwdingCode:forwarding
code
-
hops—Number of hops from the
destination to this intermediate router
-
ip-address—IP address of the
intermediate router
-
protocol—Multicast protocol
running on the intermediate router. A value of 12 indicates IGMP;
other values comply with A “ traceroute” Facility for IP Multicast – draft-ietf-idmr-traceroute-ipm-07.txt.
-
FwdingCode—Forwarding information
or error associated with this hop. For example, RPF iif indicates
that the request arrived on the expected RPF interface for this source
group. For more information about the forwarding information or error
codes, see A “ traceroute” Facility for IP Multicast – draft-ietf-idmr-traceroute-ipm-07.txt.
- Example
- host1#mtrace 100.4.4.4 40.1.1.1 232.1.1.1
- Tracing multicast route from 100.4.4.4 to 40.1.1.1 for
group 232.1.1.1 using response address 10.6.129.56
- (Press ^c to stop.)
- Received mtrace response packet of length 88
- 1. 40.1.1.1 Protocol: PIM(3) FwdingCode: RPF iif(9)
- 2. 21.2.2.2 Protocol: PIM(3) FwdingCode: Reached RP(8)
- There is no no version.
- See mtrace.
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