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Troubleshooting IP Multicast Switching (IPMS) Troubleshooting a Device that Drops Out of an IP Multicast Stream
OmniSwitch Troubleshooting Guide September 2005 page 14-5
OmniSwitch Network Configuration Guide. Also, see the “IPMS Application Example” section as it gives
a good example of how and when to use several of the IPMS commands.
To find where a multicast stream begins in your network, you can use the show ip multicast forwarding
command. This is similar to the show ip multicast groups command, but notice that “Source IP” in this
command differs in that this states the entry point of the stream (server), whereas the show ip multicast
group command displays the source IP of the IGMP join message (client). The slot/port output also gives
you the “trail” to follow in tracking down the source of the multicast stream/server.
-> show ip multicast forwarding
Source Destination
Multicast Group Source IP Type VLAN Slot/Port Type VLAN Slot/Port
-------------------+-------------------+----+----+---------+----+----+---------
224.77.1.0 10.10.10.68 NATV 1 5/13 NATV 1 5/15
224.77.205.58 10.10.10.68 NATV 1 5/13 NATV 1 5/15
Is your switch set up so that there are policies preventing multicast traffic from entering or leaving a
particular VLAN? Use the show ip multicast policy-cache command to check:
-> show ip multicast policy-cache
Policy Group Address Src Address Vlan Port Disp Time
-------+----------------+----------------+------+------+------+------
MBR 224.0.0.9 10.10.10.50 1 5/23 ACPT 133
MBR 224.0.1.22 10.10.10.65 1 5/23 ACPT 132
MBR 224.0.1.24 10.10.10.5 1 5/23 ACPT 136
MBR 224.77.0.0 10.10.10.68 1 5/13 ACPT 138
MBR 224.77.1.0 10.10.10.64 1 5/15 ACPT 259
MBR 224.77.205.58 10.10.10.64 1 5/15 ACPT 258
MBR 239.255.255.250 10.10.10.50 1 5/23 ACPT 137
MBR 239.255.255.250 10.10.10.66 1 5/23 ACPT 258
MBR 239.255.255.254 10.10.10.70 1 5/23 ACPT 259
The “DISP” column should display ACPT for “Accept.”
IPMS follows the IGMP V2 specification, which means that the queriers are elected based on the switch/
router with the lowest IP address. During startup, all switches will be listed because they all send initial
IGMP queries. After the official querier is elected, the other switches will stop flooding IGMP queries of
their own. Eventually, only one querier in the network will remain, and will be the only one listed in the
show ip multicast queriers command for all switches in the VLAN. The querier periodically sends a
Membership Query message to the all-systems group (224.0.0.1). The hosts then respond with a host
membership report message to the group address for the stream(s) they want to receive. The querier
receives the message, and adds the group to its’ membership list.
-> show ip multicast queriers
Source IP VLAN Slot/Port Expire Type
--------------------+----+---------+------+-------
10.10.10.190 1 5/1 167 Dynamic
Type of “Dynamic” means that the IP address was learned via IGMP messages, so the address should be
alive and functioning; it is worth verifying that you can ping the addresses along your path, however.