Overview Of Ip Multicasting; Multicast Terms - Dell PowerConnect B-RX Configuration Manual

Configuring IP Multicast Protocols

Overview of IP multicasting

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.
BigIron RX supports two multicast routing protocols—Distance Vector Multicast Routing Protocol
(DVMRP) and Protocol-Independent Multicast (PIM) protocol along with the Internet Group
Membership Protocol (IGMP).
PIM and DVMRP are broadcast and pruning multicast protocols that deliver IP multicast datagrams.
The protocols employ reverse path lookup check and pruning to allow source-specific multicast
delivery trees to reach all group members. DVMRP and PIM build a different multicast tree for each
source and destination host group.
Both DVMRP and PIM can concurrently operate on different ports of a BigIron RX. Also, the CAM
can hold up to 1535 IPv4 multicast entries.
NOTE
Each of the multicast protocols uses IGMP. IGMP is automatically enabled on an interface when you
configure PIM or DVMRP on an interface and is disabled on the interface if you disable PIM or
DVMRP on the interface.
The following are commonly used terms in discussing multicast-capable routers. These terms are
used throughout this chapter.

Multicast terms

The following are commonly used terms in discussing multicast-capable routers. These terms are
used throughout this chapter.
Node: Refers to a router or the BigIron RX.
Root Node: The node that initiates the tree building process. It is also the router that sends the
multicast packets down the multicast delivery tree.
Upstream: Represents the direction from which a router receives multicast data packets. An
upstream router is a node that sends multicast packets.
Downstream: Represents the direction to which a router forwards multicast data packets. A
downstream router is a node that receives multicast packets from upstream transmissions.
Group Presence: Means that a multicast group has been learned from one of the directly
connected interfaces. Members of the multicast group are present on the router.
Intermediate Nodes: Routers that are in the path between source routers and leaf routers.
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