MAC Addressing Multicasting
These are the multicasting limitations:
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OL-12577-03
If the number of multicast routes and Internet Group Management Protocol (IGMP) groups are more
than the maximum number specified by the show sdm prefer global configuration command, the
traffic received on unknown groups is flooded in the received VLAN even though the show ip igmp
snooping multicast-table privileged EXEC command output shows otherwise. The workaround is
to reduce the number of multicast routes and IGMP snooping groups to less than the maximum
supported value. (CSCdy09008)
IGMP filtering is applied to packets that are forwarded through hardware. It is not applied to packets
that are forwarded through software. Hence, with multicast routing enabled, the first few packets are
sent from a port even when IGMP filtering is set to deny those groups on that port. There is no
workaround. (CSCdy82818)
If an IGMP report packet has two multicast group records, the switch removes or adds interfaces
depending on the order of the records in the packet:
If the ALLOW_NEW_SOURCE record is before the BLOCK_OLD_SOURCE record, the
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switch removes the port from the group.
If the BLOCK_OLD_SOURCE record is before the ALLOW_NEW_SOURCE record, the
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switch adds the port to the group.
There is no workaround. (CSCec20128)
When IGMP snooping is disabled and you enter the switchport block multicast interface
configuration command, IP multicast traffic is not blocked.
The switchport block multicast interface configuration command is only applicable to non-IP
multicast traffic.
There is no workaround. (CSCee16865)
Incomplete multicast traffic can be seen under either of these conditions:
You disable IP multicast routing or re-enable it globally on an interface.
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A switch mroute table temporarily runs out of resources and recovers later.
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The workaround is to enter the clear ip mroute privileged EXEC command on the interface.
(CSCef42436)
After you configure a switch to join a multicast group by entering the ip igmp join-group
group-address interface configuration command, the switch does not receive join packets from the
client, and the switch port connected to the client is removed from the IGMP snooping forwarding
table.
Use one of these workarounds:
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Cancel membership in the multicast group by using the no ip igmp join-group group-address
interface configuration command on an SVI.
Disable IGMP snooping on the VLAN interface by using the no ip igmp snooping vlan vlan-id
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global configuration command. (CSCeh90425)
Release Notes for the Cisco Catalyst Blade Switch 3020 for HP, Cisco IOS Release 12.2(37)SE and Later
Limitations and Restrictions
9
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