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Configuring PIM Sparse-Dense Mode

Understanding PIM Sparse-Dense Mode

Sparse-dense mode, as the name implies, allows the interface to operate on a per-group basis in either sparse or dense mode. A group specified as dense is not mapped to an RP. Instead, data packets destined for that group are forwarded by means of PIM dense-mode rules. A group specified as sparse is mapped to an RP, and data packets are forwarded by means of PIM sparse-mode rules.

For information about PIM sparse-mode and PIM dense-mode rules, see Understanding PIM Sparse Mode and Understanding PIM Dense Mode.

See Also

Mixing PIM Sparse and Dense Modes

It is possible to mix PIM dense mode, PIM sparse mode, and PIM source-specific multicast (SSM) on the same network, the same routing device, and even the same interface. This is because modes are effectively tied to multicast groups, an IP multicast group address must be unique for a particular group's traffic, and scoping limits enforce the division between potential or actual overlaps.

Note:

PIM sparse mode was capable of forming shortest-path trees (SPTs) already. Changes to PIM sparse mode to support PIM SSM mainly involved defining behavior in the SSM address range, because shared-tree behavior is prohibited for groups in the SSM address range.

A multicast routing device employing sparse-dense mode is a good example of mixing PIM modes on the same network or routing device or interface. Dense modes are easy to support because of the flooding, but scaling issues make dense modes inappropriate for Internet use beyond very restricted uses.

Configuring PIM Sparse-Dense Mode Properties

Sparse-dense mode allows the interface to operate on a per-group basis in either sparse or dense mode. A group specified as “dense” is not mapped to an RP. Instead, data packets destined for that group are forwarded by means of PIM dense mode rules. A group specified as “sparse” is mapped to an RP, and data packets are forwarded by means of PIM sparse-mode rules. Sparse-dense mode is useful in networks implementing auto-RP for PIM sparse mode.

By default, PIM is disabled. When you enable PIM, it operates in sparse mode by default.

You can configure PIM sparse-dense mode globally or for a routing instance. This example shows how to configure PIM sparse-dense mode globally on all interfaces, specifying that the groups 224.0.1.39 and 224.0.1.40 are using dense mode.

To configure the router properties for PIM sparse-dense mode:

  1. Configure the dense-mode groups.
  2. Configure all interfaces on the routing device to use sparse-dense mode. When configuring all interfaces, exclude the fxp0.0 management interface by adding the disable statement for that interface.
  3. Monitor the operation of PIM sparse-dense mode by running the show pim interfaces, show pim join, show pim neighbors, and show pim statistics commands.

See Also

Related Documentation