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Multicast Filtering
RS400 195 ROS™ v3.5
8 Multicast Filtering
ROS™ accomplishes Multicast Filtering through the following ways:
1. Static Multicast Groups
2. Use of the Internet Group Management Protocol (IGMP) snooping.
ROS™ Multicast Filtering provides you with the following features:
• Support for up to 256 Multicast Groups (either static or dynamic).
• Ability to prioritize a Static Multicast Group via Class-of-Service
• Industry standard support of IGMP (RFC 1112, RFC 2236) versions 1 and 2 in active and
passive roles.
Note: ROS
™
IGMP Snooping supports multicast routers using IGMP version 2 and hosts using either IGMP
version 1 or 2.
• Ability to enable or disable IGMP on a per VLAN basis.
• Multicast Routers may be statically configured or dynamically recognized by IGMP.
• “Routerless” IGMP operation.
8.1 IGMP
IGMP is used by IP hosts to report their host group memberships to multicast routers. As hosts
join and leave specific multicast groups, streams of traffic are directed to or withheld from that
host.
The IGMP protocol operates between multicast routers and IP hosts. When an unmanaged
switch is placed between multicast routers and their hosts, the multicast streams will be
distributed to all ports. This may introduce significant traffic onto ports that do not require it and
receive no benefit from it.
RuggedCom products with IGMP Snooping enabled will act upon IGMP messages sent from the
router and the host, restricting traffic streams to the appropriate LAN segments.
8.1.1 Router and Host IGMP Operation
The following figure provides a simple example of IGMP use. One “producer” IP host (P1) is
generating two IP multicast streams, M1 and M2. There are four potential “consumers” of these
streams, C1 through C4.
The multicast router discovers which host wishes to subscribe to which stream by sending
general membership queries to each of the segments.