Switch User Manual

46 An Introduction to IP Routing Protocols
— The stack will continue to run normally with the base unit controlling
Layer 3 and DRP functionality.
— If the non-operational non-base unit does not rejoin the stack, no
Layer 3 or DRP functionality will run on it.
IGMP snooping
The Nortel Ethernet Routing Switch 5500 Series can sense Internet Group
Management Protocol (IGMP) host membership reports from attached
stations and use this information to set up a dedicated path between the
requesting station and a local IP Multicast router. After the pathway is
established, the Nortel Ethernet Routing Switch 5500 Series switch blocks
the IP Multicast stream from exiting any other port that does not connect to
another host member, thus conserving bandwidth. The following section
describes how Nortel Ethernet Routing Switch 5500 Series switches provide
the same benefit as IP Multicast routers, but in the local area.
IGMP is used by IP Multicast routers to learn about the existence of host
group members on their directly attached subnets (see RFC 2236). The IP
Multicast routers get this information by broadcasting IGMP queries and
listening for IP hosts reporting their host group memberships. This process
is used to set up a client/server relationship between an IP Multicast source
that provides the data streams and the clients that want to receive the data.
By default, unknown multicast traffic is flooded to all ports in a VLAN. In
situations in which there is a multicast transmitter that is not doing IGMP
and there are no multicast receivers, the traffic transmitted by the transmitter
is flooded.
The CLI commands for IGMP allow the sending of all unknown multicast
traffic to IGMP static router ports only. This traffic will not be forwarded to
dynamically discovered m-router ports. If it is desirable to forward unknown
unicast traffic to certain ports only, those ports can be set as static m-router
ports.
• When disabled, the Nortel Ethernet Routing Switch 5500 Series switch
treats unknown multicast traffic as it does broadcast traffic (flood). This
is the default behavior.
•
User settings for the Unknown Multicast No Flood feature is stored in
NVRAM. In a stack, if settings on different units differ, the Base Unit
setting will take precedence. This feature can be enabled or disabled
at any time.
•
Nortel Networks recommends this feature be enabled when IGMP
snooping is enabled.
Nortel Ethernet Routing Switch 5500 Series
Configuration-IP Routing Protocols
NN47200-503 03.01 Standard
5.1 27 August 2007
Copyright © 2005-2007, Nortel Networks
.