Install guide

26 Software Reference
entry made for port 7 only. The IGMP group received on port 7 will not be
added to port 9.
The all-groups disabled ports can be viewed in the output of the show ip igmp
and show igmpsnooping commands.
IGMP Filtering
IGMP filtering lets you manage the distribution of multicast services on each
switch port by controlling which multicast groups the hosts attached to a
switch port can join.
IGMP filtering is applied to multicast streams forwarded by IGMP, IGMP
Snooping, or MVR.
IGMP filtering and throttling can be applied separately, or together, on the
same switch port. Filtering is applied first, and any multicast group
memberships passed by the filter are further subjected to the limits imposed by
throttling. For more information about IGMP throttling, see “IGMP Throttling”
on page 28.
Static associations of switch ports and multicast groups are not affected by
IGMP filtering.
When to use
IGMP filters
Use an IGMP filter to:
■ limit the multicast groups a downstream port can be a member of, by
applying a filter that matches IGMP report messages to the port
■ limit the impact of misbehaving devices by applying a filter that matches
inappropriate IGMP messages, for example, query messages on a
downstream port or leave messages on an upstream port
Filter format An IGMP filter consists of zero or more entries. An entry consists of:
■ A multicast address range to match against. Address ranges in multiple
entries can overlap.
■ An IGMP message type to match—query, report, or leave.
■ An action to take (include or exclude) when an IGMP message is received
that matches the multicast address range and message type.
Matching against a
filter
When an IGMP filter is applied to a switch port the following happens:
1. IGMP matches incoming IGMP messages from the switch port against each
entry in the filter applied to the port.
2. If the message type and group address in the IGMP message matches a filter
entry, IGMP takes the action specified by the filter entry:
• If the action is include, IGMP processes the IGMP message as normal.
• If the action is exclude, IGMP excludes the IGMP message from normal
IGMP processing and discards the packet.
Filter processing stops when a match is found.
3. If the IGMP message does not match any entry in the filter, but the filter
contains at least one entry that matches the message type, then IGMP
excludes the IGMP message from normal IGMP processing and discards the
packet.