Chapter 11: Troubleshooting IPv4 and IPv6
multicast routing
This section describes commands that you use to troubleshoot multicast routing.
Troubleshooting multicast routing
Begin
troubleshooting multicast routing issues by verifying that the IP interfaces in the system
are "up". Use the following commands to check the status of IP interfaces: show ip
interfaces format brief (IPv4) show ipv6 interfaces format brief (IPv6)
If you use PIM as the multicast routing protocol, it relies on the routes learned through the
unicast routing protocols for building the multicast delivery trees. Troubleshooting for multicast
routing with PIM, therefore, should start with the verification of unicast reachability. For more
information, see
Troubleshooting unicast routing on page 125
.
The multicast route tracing feature is also useful in tracing the multicast distribution tree for
specific groups and sources in the network. The multicast traceroute tool (mtrace) is similar to
the traceroute tool for unicast traffic. Use mtrace to trace IPv4 multicast traffic flow routes.
Unlike unicast route tracing, multicast route tracing basically prints a path from the receiver to
the source. Issue the following multicast traceroute command from the root of the CLI: mtrace
<source> [<destination>] [<group>] [<ttl>]
Table 65: Variable definitions
Variable Value
<source> IP address of a multicast-capable source.
You must enter information for this
parameter.
[<destination>] Address of the unicast destination. This
parameter is optional. If omitted, the
multicast
traceroute starts from the system at
which you enter the command.
[<group>] Multicast address of the group to be traced.
This parameter is optional.
[<ttl>] Time-to-live (TTL) threshold for a multicast
trace
request. The range of values is 1 to 255
router hops. This parameter is optional. The
default value is 255.
Troubleshooting August 2013 153
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