group. This means that IGMP traffic will be forwarded on a specific port only
if an IGMP host or multicast router is connected to the port.
Blocked Causes the switch to drop all IGMP transmissions received from a specific
port. Outgoing queries are not blocked on the port.
Forward Causes the switch to forward all IGMP and IP multicast transmissions through
the port.
This feature helps to conserve IP addresses by enabling IGMP to run on VLANs that do
not have an IP address. See “Operation with or without IP addressing” (page 15).
Operation with or
without IP
addressing
The switch performs this function for IGMP on VLANs having an IP address when there is
no other device in the VLAN acting as querier. See “Using the switch as querier” (page 23).
Querier capability
To configure high priority settings for traffic, see “Quality of Service: managing bandwidth more
effectively” in the Advanced Traffic Management Guide.
NOTE: Whenever IGMP is enabled, the switch generates an Event Log message indicating
whether querier functionality is enabled.
IP multicast traffic groups are identified by IP addresses in the range of 224.0.0.0 to
239.255.255.255. Also, incoming IGMP packets intended for reserved, or "well-known" multicast
addresses, automatically flood through all ports (except the port on which the packets entered the
switch.) For more on this topic, see “Well-known or reserved multicast addresses excluded from IP
multicast filtering” (page 24).
For more information about IGMP, see “How IGMP operates” (page 14).
Number of IP multicast addresses allowed
The number of IGMP filters (addresses) and static multicast filters available is 2,038. Additionally,
16 static multicast filters are allowed, If multiple VLANs are configured, then each filter is counted
once per VLAN in which it is used.
Configuring and displaying IGMP (CLI)
Viewing IGMP configuration for VLANs
Syntax:
show ip igmp [vlan <vid>]
Displays IGMP configuration for a specified VLAN or for all VLANs on the switch.
8 Multimedia Traffic Control with IP Multicast (IGMP)
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