LevelOne GTL-2691 - Manual (Page 705)

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21
M
ULTICAST
R
OUTING
This chapter describes the following multicast routing topics:
◆ Enabling Multicast Routing Globally – Describes how to globally enable
multicast routing.
◆ Displaying the Multicast Routing Table – Describes how to display the
multicast routing table.
◆ Configuring PIM for IPv4 – Describes how to configure PIM-DM and
PIM-SM for IPv4.
◆ Configuring PIMv6 for IPv6 – Describes how to configure PIM-DM and
PIM-SM (Version 6) for IPv6.
O VERVIEW
This router can route multicast traffic to different subnetworks using
Protocol-Independent Multicasting - Dense Mode or Sparse Mode (PIM-DM
or PIM-SM) for IPv4, as well as PIM-DM for IPv6. PIM for IPv4 (also called
PIMv4 in this manual) relies on messages sent from IGMP-enabled Layer 2
switches and hosts to determine when hosts want to join or leave multicast
groups. PIM for IPv6 (also called PIMv6 in this manual) uses the Multicast
Listener Discovery (MLDv1) protocol which is the IPv6 equivalent to
IGMPv2. PIM-DM is designed for networks where the probability of
multicast group members is high, such as a local network. PIM-SM is
designed for networks where the probability of multicast group members is
low, such as the Internet.
Also, note that if PIM is not enabled on this router or another multicast
routing protocol is used on the network, the switch ports attached to a
multicast router can be manually configured to forward multicast traffic
(see "Specifying Static Interfaces for a Multicast Router" on page 519 ).
Configuring PIM-DM
PIM-DM floods multicast traffic downstream, and calculates the shortest-
path, source-rooted delivery tree between each source and destination
host group. Other multicast routing protocols, such as DVMRP, build their
own source-rooted multicast delivery tree (i.e., a separate routing table)
that allows it to prevent looping and determine the shortest path to the
source of the multicast traffic. PIM-DM also builds a source-rooted
multicast delivery tree for each multicast source, but uses information from
the router’s unicast routing table, instead of maintaining its own multicast
routing table, making it routing protocol independent.