C
HAPTER
21
| Multicast Routing
Configuring PIM for IPv4
– 552 –
topology changes (sources joining or leaving a multicast group) before
the default three-minute state timeout expires.
This command is only effectively for interfaces of first hop, PIM-DM
routers that are directly connected to the sources of multicast groups.
Sparse-Mode Attributes
◆ DR Priority – Sets the priority advertised by a router when bidding to
become the Designated Router (DR). (Range: 0-4294967294;
Default: 1)
More than one PIM-SM router may be connected to an Ethernet or
other shared-media LAN. If multicast hosts are directly connected to
the LAN, then only one of these routers is elected as the DR, and acts
on behalf of these hosts, sending periodic Join/Prune messages toward
a group-specific RP for each group. A single DR is elected per interface
(LAN or otherwise) using a simple election process.
The router with the highest priority configured on an interface is elected
as the DR. If more than one router attached to this interface uses the
same priority, then the router with the highest IP address is elected to
serve as the DR.
If a router does not advertise a priority in its hello messages, it is
assumed to have the highest priority and is elected as the DR. If more
than one router is not advertising its priority, then the router with the
highest IP address is elected to serve as the DR.
◆ Join/Prune Interval – Sets the interval at which join/prune messages
are sent. (Range: 1-65535 seconds; Default: 60 seconds)
By default, the switch sends join/prune messages every 60 seconds to
inform other PIM-SM routers about clients who want to join or leave a
multicast group.
Use the same join/prune message interval on all PIM-SM routers in the
same PIM-SM domain, otherwise the routing protocol’s performance
will be adversely affected.
The multicast interface that first receives a multicast stream from a
particular source forwards this traffic only to those interfaces on the
router that have requests to join this group. When there are no longer
any requesting groups on that interface, the leaf node sends a prune
message upstream and enters a prune state for this multicast stream.
The protocol maintains both the current join state and the pending RPT
prune state for this (source, group) pair until the join/prune interval
timer expires.
WEB INTERFACE
To configure PIM interface settings:
1. Click Routing Protocol, PIM, Interface.
2. Modify any of the protocol parameters as required.
3. Click Apply.
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