Users Guide

934 Layer-2 Multicast Features
Snooping Switch Restrictions
MAC Address-Based Multicast Group
The L2 multicast forwarding table consists of the Multicast group MAC
address filtering entries. For IPv4 multicast groups, 16 IP multicast group
addresses map to the same multicast MAC address. For example, 224.1.1.1
and 225.1.1.1 map to the MAC address 01:00:5E:01:01:01, and IP addresses in
the range [224-239].3.3.3 map to 01:00:5E:03:03:03. As a result, if a host
requests 225.1.1.1, then it might receive the multicast traffic of group
226.1.1.1 as well.
Topologies Where the Multicast Source Is Not Directly Connected to the
Querier
If the multicast source is not directly connected to a multicast querier, the
multicast stream is forwarded to any router ports on the switch (within the
VLAN). Because multicast router queries are flooded to all ports in the
VLAN, intermediate IGMP snooping switches will receive the multicast
stream from the multicast source and forward it to the multicast router.
Using Static Multicast MAC Configuration
If configuring static multicast MAC group addresses on a port in a VLAN, it is
necessary to configure all ports in the VLAN over which it is desired that the
group traffic flow (both host and router) on all switches. IGMP snooping does
not dynamically add ports to a VLAN for a multicast group when a static
entry is configured for that group in the VLAN. This restriction applies to
both multicast router-connected ports and host-connected ports.
IGMP Snooping and GMRP
IGMP snooping and GMRP are not compatible. Only one of IGMP snooping
or GMRP should be configured to filter multicast groups for any VLAN.
Simultaneous operation of GMRP and IMGP snooping is not supported and
will lead to undesirable results, such as flooding in the VLAN due to the
inability to identify multicast router ports.