400
Chapter 10
Configuring Multicast
This tells the router to become a member of the 224.2.127.254 multicast
group. Joining a group facilitates troubleshooting multicast connectivity
issues as well.
Troubleshooting IP Multicast Connectivity
Multicast can be a very difficult protocol to troubleshoot. There are, how-
ever, a few basic tools (mostly show commands) that can provide you with
enough information to verify that connectivity is active or whether other
steps, such as debugging, are needed to troubleshoot the problem.
If you do need to debug a multicast-enabled interface, you must first dis-
able the multicast fast switching on the interface. This is done so that the
debug messages can be logged. The command to disable fast switching is no
ip mroute-cache
. The normal unicast fast (or other forms of) switching
may be left enabled.
You are familiar with the troubleshooting tools for unicast connectivity,
Ping and traceroute. Well, these tools are also available for troubleshooting
multicast connectivity. There is one minor difference, though: multicast requires
a special version of traceroute, called mtrace or "multicast-traceroute."
Ping
Once a device on the network becomes a member of a group, it can be iden-
tified by its layer 3 multicast address as well as the layer 2 MAC address.
Because the device has an active address on its interface, it can respond to
ICMP request packets. Here is an example:
RouterA#ping
Protocol [ip]:
Target IP address: 224.2.143.55
Repeat count [1]: 5
Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 224.2.143.55, timeout is
2 seconds:
.!!!!
RouterA#
Copyright ©2000 SYBEX , Inc., Alameda, CA
www.sybex.com