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Chapter 11 Avaya P330 Layer 2 Features
Avaya P332GT-ML User’s Guide 75
IP Multicast Filtering
Overview
IP Multicast is a method of sending a single copy of an IP packet to multiple
destinations. It can be used by different applications including video streaming and
video conferencing.
The Multicast packet is forwarded from the sender to the recipients, duplicated only
when needed by routers along the way and sent in multiple directions such that it
reaches all the members of the Multicast group. Multicast addresses are a special
kind of IP addresses (class D), each identifying a multicast group. Stations join and
leave multicast groups using IGMP. This is a control-plane protocol through which
IP hosts register with their router to receive packets for certain multicast addresses.
IP multicast packets are transmitted on LANs in MAC multicast frames. Traditional
LAN switches flood these multicast packets like broadcast packets to all stations in
the VLAN. In order to avoid sending multicast packets where they are not required,
multicast filtering functions may be added to the layer 2 switches, as described in
IEEE standard 802.1D. Layer 2 switches capable of multicast filtering send the
multicast packets only to ports connecting members of that multicast group. This is
typically based on IGMP snooping.
The Avaya P330 supports multicast filtering. The P330 learns which switch ports
need to receive which multicast packets and configures the necessary information
into the switch's hardware tables. This learning is based on IGMP (version 1 or 2)
snooping.
The multicast filtering function in the P330 is transparent to the IP hosts and routers.
It does not affect the forwarding behavior apart from filtering multicast packets
from certain ports where they are not needed. To the ports that do get the multicast,
forwarding is performed in the same way as if there was no filtering, and the
multicast packet will not be sent to any ports that would not receive it if there was
no filtering.
The multicast filtering function operates per VLAN. A multicast packet arriving at
the device on a certain VLAN will be forwarded only to a subset of the ports of that
VLAN. If VLAN tagging mode is used on the output port, then the multicast packet
will be tagged with the same VLAN number with which it arrived. This is
interoperable with multicast routers that expect Layer 2 switching to be done
independently for each VLAN.
IP Multicast Filtering configuration is associated with the setting up of three timers:
•The Router Port Pruning timer ages out Router port information if IGMP
queries are not received within the configured time.
•The Client Port Pruning time is the time after the P330 switch reset that the
filtering information is learned by the switch but not configured on the ports.
•The Group Filtering Delay time is the time that the switch waits between
becoming aware of a Multicast group on a certain VLAN and starting to filter
traffic for this group.