Avaya P332G-ML manual IP Multicast Filtering, Overview

Chapter 11 Avaya P330 Layer 2 Features

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.

Avaya P332G-ML User’s Guide 75