CANOGA PERKINS 9175 Configuration Guide - Manual (Page 143)

CanogaOS Configuration Guide
24-1
24 Configuring IP Multicast-Routing
24.1 Multicast Overview
Multicast protocols allow a group or channel to be accessed over different networks by
multiple stations (clients) for the receipt and transmit of multicast data.
Distribution of stock quotes, video transmissions such as news services and remote
classrooms, and video conferencing are all examples of applications that use multicast
routing.
• Internet Group Management Protocol (IGMP) is used among hosts on a LAN and
the routers (and multilayer switches) on that LAN to track the multicast groups of
which hosts are members.
• Protocol-Independent Multicast (PIM) protocol is used among routers and
multilayer switches to track which multicast packets to forward to each other and
to their directly connected LANs. PIM has two modes: Sparse-mode and
Dense-mode. Currently, we only support Sparse-mode
24.2 IGMP Configuration
To participate in IP multicasting, multicast hosts, routers, and multilayer switches must
have the IGMPoperating. This protocol defines the querier and host roles:
• A querier is a network device that sends query messages to discover which
network devices are members of a given multicast group.
• A host is a receiver that sends report messages (in response to query messages)
to inform a querier of a host membership.
A set of queriers and hosts that receive multicast data streams from the same source is
called a multicast group. Queriers and hosts use IGMP messages to join and leave
multicast groups.
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. How active a
multicast group is and what members it has can vary from group to group and from time
to time. A multicast group can be active for a long time, or it can be very short-lived.
Membership in a group can constantly change. A group that has members can have no
activity.
IGMP packets are sent using these IP multicast group addresses:
• IGMP general queries are destined to the address 224.0.0.1 (all systems on a
subnet).
• IGMP group-specific queries are destined to the group IP address for which the
switch is querying.
• IGMP group membership reports are destined to the group IP address for which
the switch is reporting.
• IGMP Version 2 (IGMPv2) leave messages are destined to the address 224.0.0.2
(all-multicast-routers on a subnet). In some old host IP stacks, leave messages