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Configuring IP Multicast Routing
Enabling PIM on an Interface
IPC-404
Cisco IOS IP Configuration Guide
See the “PIM Dense Mode Example” section later in this chapter for an example of how to configure a
PIM interface in dense mode.
Enabling Sparse Mode
To configure PIM on an interface to be in sparse mode, use the following command in interface
configuration mode:
See the “PIM Sparse Mode Example” section later in this chapter for an example of how to configure a
PIM interface in sparse mode.
Enabling Sparse-Dense Mode
If you configure either the ip pim sparse-mode or ip pim dense-mode interface configuration
command, then 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. In this
case, 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. You must have an RP if the interface is in sparse-dense mode, and
you want to treat the group as a sparse group.
If you configure sparse-dense mode, the idea of sparseness or denseness is applied to the group on the
router, 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. Thus, there is no
need to configure a default RP at the leaf routers.
When an interface is treated in dense mode, it is populated in the outgoing interface list of a multicast
routing table when either of the following conditions is true:
• Members or DVMRP neighbors are on the interface.
• There are PIM neighbors and the group has not been pruned.
When an interface is treated in sparse mode, it is populated in the outgoing interface list of a multicast
routing table when either of the following conditions is true:
• Members or DVMRP neighbors are on the interface.
• An explicit join message has been received by a PIM neighbor on the interface.
To enable PIM to operate in the same mode as the group, use the following command in interface
configuration mode:
Command Purpose
Router(config-if)# ip pim dense-mode
Enables PIM dense mode on the interface.
Command Purpose
Router(config-if)# ip pim sparse-mode
Enables PIM sparse mode on the interface.