Chapter 16
| Multicast Filtering
Layer 2 IGMP (Snooping and Query)
– 478 –
Setting IGMP
Snooping Status
per Interface
Use the Multicast > IGMP Snooping > Interface (Configure VLAN) page to configure
IGMP snooping attributes for a VLAN. To configure snooping globally, refer to
“Configuring IGMP Snooping and Query Parameters” on page 470.
Command Usage
Multicast Router Discovery
There have been many mechanisms used in the past to identify multicast routers.
This has lead to interoperability issues between multicast routers and snooping
switches from different vendors. In response to this problem, the Multicast Router
Discovery (MRD) protocol has been developed for use by IGMP snooping and
multicast routing devices. MRD is used to discover which interfaces are attached to
multicast routers, allowing IGMP-enabled devices to determine where to send
multicast source and group membership messages. (MRD is specified in draft-ietf-
magma-mrdisc-07.)
Multicast source data and group membership reports must be received by all
multicast routers on a segment. Using the group membership protocol query
messages to discover multicast routers is insufficient due to query suppression.
MRD therefore provides a standardized way to identify multicast routers without
relying on any particular multicast routing protocol.
Note:
The default values recommended in the MRD draft are implemented in the
switch.
Multicast Router Discovery uses the following three message types to discover
multicast routers:
◆ Multicast Router Advertisement – Advertisements are sent by routers to
advertise that IP multicast forwarding is enabled. These messages are sent
unsolicited periodically on all router interfaces on which multicast forwarding
is enabled. They are sent upon the occurrence of these events:
■
Upon the expiration of a periodic (randomized) timer.
■
As a part of a router's start up procedure.
■
During the restart of a multicast forwarding interface.
■
On receipt of a Solicitation message.
◆ Multicast Router Solicitation – Devices send Solicitation messages in order to
solicit Advertisement messages from multicast routers. These messages are
used to discover multicast routers on a directly attached link. Solicitation
messages are also sent whenever a multicast forwarding interface is initialized
or re-initialized. Upon receiving a solicitation on an interface with IP multicast
forwarding and MRD enabled, a router will respond with an Advertisement.
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