User manual

Chapter 4 Avaya P460 Layer 2 Features
IP Multicast Filtering Configuration
Overview
IP Multicast is a method of sending a single copy of an IP packet to multiple
destinations. Different applications including video streaming and video
conferencing can use IP multicast.
The Multicast packet is forwarded from the sender to the recipients, duplicated only
when needed by routers along the way. The packet is 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 can be added to the layer 2 switches. This is described
in the 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
usually based on IGMP snooping.
The Avaya P460 includes multicast filtering support. The P460 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. Using the learned information, IP multicast packets are
forwarded only to ports connecting members of that multicast group.
The multicast filtering function in the P460 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. 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 is 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
is 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 P460 switch reset that the
filtering information is learned by the switch but not configured on the ports.
34 Avaya P460 Configuration Guide