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33-15
Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 33 Configuring IP Multicast
Configuring IP Multicast Routing
encapsulated and sent toward the RP. When no RP is known, the packet is flooded in a dense-mode
fashion. If the multicast traffic from a specific source is sufficient, the receiver’s first-hop router can send
join messages toward the source to build a source-based distribution tree.
There is no default mode setting. By default, multicast routing is disabled on an interface.
Enabling Dense Mode
To configure PIM on an interface to be in dense mode, enter this command:
For an example of how to configure a PIM interface in dense mode, see the “PIM Dense Mode Example”
section.
Enabling Sparse Mode
To configure PIM on an interface to be in sparse mode, enter this command:
For an example of how to configure a PIM interface in sparse mode, see the “PIM Sparse Mode
Example” section.
Enabling Sparse-Dense Mode
When you enter either the ip pim sparse-mode or ip pim dense-mode command, sparseness or
denseness is applied to the interface as a whole. However, some environments might require PIM to run
in a single region in sparse mode for some groups and in dense mode for other groups.
An alternative to enabling only dense mode or only sparse mode is to enable sparse-dense mode. The
interface is treated as dense mode if the group is in dense mode; the interface is treated in sparse mode
if the group is in sparse mode. If you want to treat the group as a sparse group, and the interface is in
sparse-dense mode, you must have an RP.
If you configure sparse-dense mode, the idea of sparseness or denseness is applied to the group on the
switch, and the network manager should apply the same concept throughout the network.
Another benefit of sparse-dense mode is that Auto-RP information can be distributed in a dense-mode
manner; yet, multicast groups for user groups can be used in a sparse-mode manner. You do not need to
configure a default RP at the leaf routers.
When an interface is treated in dense mode, it is populated in a multicast routing table’s outgoing
interface list when either of the following is true:
• When members or DVMRP neighbors exist on the interface
• When PIM neighbors exist and the group has not been pruned
Command Purpose
Switch(config-if)# ip pim dense-mode
Enables dense-mode PIM on the interface.
Command Purpose
Switch(config-if)# ip pim
sparse-mode
Enables sparse-mode PIM on the interface.