Configuring IP Multicast Routing
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interface, allowing the interface to listen for IGMP membership reports.
Here is an example of enabling IP PIM sparse mode multicast on an interface:
RouterA#conf t
Enter configuration commands, one per line. End with
CNTL/Z.
RouterA(config)#interface FastEthernet3/0
RouterA(config-if)#ip pim sparse-mode
RouterA(config-if)#^Z
RouterA#
Here is a look at the interface configuration after the execution shown
above:
!
interface FastEthernet3/0
ip address 172.16.21.4 255.255.255.0
no ip directed-broadcast
ip pim sparse-mode
!
IP PIM Sparse-Dense Mode
The name of this command gives an indication of the functionality it pro-
vides. Due to the increasing use of multicast and the variety of applications
available today, it is best to configure an interface to be able to use both
sparse mode and dense mode. With the previous commands, the interface
was assigned the operating mode, and the interface could not change
between modes depending on the need at the time.
PIM sparse-dense mode configuration now allows the interface to use
whichever forwarding method is needed by the application or multicast
group. The interface uses the multicast group notation to decide which mode
it needs to operate in. If the interface sees something with the notation (S, G),
it will operate in dense mode. If the interface sees notation similar to (*, G),
the interface will operate in sparse mode.
An added benefit of implementing sparse-dense mode on the interfaces is
the elimination of the need to hard-configure the RP at every leaf router. The
Auto-RP information is sent out across the network using dense mode
forwarding.
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