426
Configuring IGMP Snooping and MVR
Information About IGMP Snooping and MVR
You can configure an IGMP snooping querier to support IGMP snooping in subnets without multicast interfaces because
the multicast traffic does not need to be routed. For more information about the IGMP snooping querier, see Configuring
the IGMP Snooping Querier, page 437.
If a port spanning-tree, a port group, or a VLAN ID change occurs, the IGMP snooping-learned multicast groups from
this port on the VLAN are deleted.
When you enable IGMP Immediate Leave, the switch immediately removes a port when it detects an IGMP Version 2 leave
message on that port. You should only use the Immediate-Leave feature when there is a single receiver present on every
port in the VLAN.
IGMP Versions
The switch supports IGMP Version 1, IGMP Version 2, and IGMP Version 3. These versions are interoperable on the
switch. For example, if IGMP snooping is enabled on an IGMPv2 switch and the switch receives an IGMPv3 report from
a host, the switch can forward the IGMPv3 report to the multicast router.
Note: The switch supports IGMPv3 snooping based only on the destination multicast MAC address. It does not support
snooping based on the source MAC address or on proxy reports.
An IGMPv3 switch supports Basic IGMPv3 Snooping Support (BISS), which includes support for the snooping features
on IGMPv1 and IGMPv2 switches and for IGMPv3 membership report messages. BISS constrains the flooding of
multicast traffic when your network includes IGMPv3 hosts. It constrains traffic to approximately the same set of ports as
the IGMP snooping feature on IGMPv2 or IGMPv1 hosts.
Note: IGMPv3 join and leave messages are not supported on switches running IGMP filtering or MVR.
An IGMPv3 switch can receive messages from and forward messages to a device running the Source Specific Multicast
(SSM) feature.
Joining a Multicast Group
When a host connected to the switch wants to join an IP multicast group and it is an IGMP Version 2 client, it sends an
unsolicited IGMP join message, specifying the IP multicast group to join. Alternatively, when the switch receives a general
query from the router, it forwards the query to all ports in the VLAN. IGMP Version 1 or Version 2 hosts wanting to join
the multicast group respond by sending a join message to the switch. The switch CPU creates a multicast
forwarding-table entry for the group if it is not already present. The CPU also adds the interface where the join message
was received to the forwarding-table entry. The host associated with that interface receives multicast traffic for that
multicast group. See Figure 65 on page 427.
To Next Page
Loading...
Need help?
General
