While the IEEE 802.1D standard defines the learning and forwarding behavior of a bridge for unicast data, it does not provide a method for the bridge to learn the reachability of hosts that belong to a multicast group. As a result, forwarding of multicast data requires the data to be forwarded over all the ports other than the received port. This results in unnecessary wastage of network resources and bandwidth since there may not be valid receivers for the multicast data on some ports.
Internet Group Management Protocol (IGMP) as defined in RFCs 1112, 2236 and 3376, enables hosts on a subnet to dynamically enable their group membership with the edge router.
In the recent years networking devices - specifically layer 2 switches have been supporting the ability to derive layer 2 multicast group forwarding information by processing the layer 3 Internet Group Management Protocol (IGMP) packets. Thus layer 2 switches can use IGMP snooping to configure switch ports dynamically so that IP multicast traffic is forwarded only to those ports associated with IP multicast hosts. The IETF draft - draft-ietf-magma-snoop-12.txt, describes the recommendations for such IGMP snooping devices.
ATTEST IGS test cases verify whether IGMP PDUs and VLAN tagged IGMP PDUs are forwarded according to IGMP Forwarding rules. Tests also verify that the forwarding of multicast data takes place according to the routing information created based on snooped IGMP PDUs.
Together with other Layer-2 Switch Test Suites such as VLAN, MSTP, RSTP, STP, 802.1X and LACP, Net-O2 provides one of the most comprehensive solutions for conformance testing of Ethernet Switches. Layer-3 IP Multicast Test suites are also available.
