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Multicast Traffic Management
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routing protocol, such as Protocol-Independent Multicast (PIM), routers
maintain forwarding tables that they use to forward multicast datagrams.
Packets delivered to members of the multicast group are identified by a
single multicast group address. Any host, regardless of whether it is a
member of a group, can send to a group. However, only the members of a
group receive the message. Membership in a multicast group is dynamic;
hosts can join and leave at any time. There is no restriction on the location or
number of members in a multicast group. A host can be a member of more
than one multicast group at a time.
IGMP Snooping
A traditional layer-2 switch is unable to determine which end stations on the
LAN are interested in which multicast groups. To avoid unnecessary
flooding, the switch may use IGMP Snooping. That means the switch listens
to IGMP messages to learn which ports want multicast traffic from which
multicast groups. The switch inserts the correct Ethernet multicast address
into the forwarding table for the ports where an end station has joined a
multicast group.
GMRP - GARP Multicast Registration Protocol
A limitation of IGMP Snooping is that all IP multicast traffic must be
examined to build the tables necessary to prune the multicasts. GMRP, an
IEEE standard, provides a mechanism for end stations to directly inform a
switch of its interest in a particular multicast group.
When it wants to join a group, an end station sends a GARP packet to the
GMRP multicast address, 01:80:00:00:20. Switches that support GMRP use
such GARP packets to notify routers of the presence of group members, and
to configure their forwarding tables to avoid unnecessary flooding.
K Note: GMRP operates at layer 2, while IGMP is an IP
protocol and operates at layer 3.
For more information about GMRP, see ANSI/IEEE Std. 802.1D -- 1998
Edition, which includes the 802.1p standard. See <http://www.ieee.org> for
more information.
IP Multicast Quality of Service - RSVP
The IntraCore 8000 also supports the industry standard Resource
Reservation Protocol (RSVP). RSVP allows an end station to reserve
resources across the net in an attempt to maintain quality of service from a
multicast provider. The IntraCore 8000 monitors RSVP messages so it can