Configuring C-RPs on PIM-SM routers

An RP candidate advertises its availability, IP address, and the multicast group or range of groups it supports. The commands in this section are used to configure C-RP operation. The sequence of steps is as follows:

Specify the source IP VLAN.
Enable C-RP operation.
Option: enable or disable specific multicast address groups.


	NOTE: Before configuring BSR, RP, and SNMP trap operation for PIM-SM, it is necessary to enable PIM-SM on at least one VLAN on the router.

Specifying the source IP VLAN (optionally configuring multicast groups or range of groups)

Specifying the source IP VLAN ID automatically configures the C-RP to support all multicast groups (unless you include an individual group or range of groups in the command.) The recommended approach is to allow all multicast groups unless you have a reason to limit the permitted groups to a specific set.

Syntax:

[no] rp-candidate source-ip-vlan [vid] [group-prefix group-addr/mask]

[no] router pim rp-candidate source-ip-vlan [vid] [group-prefix group-addr/mask]

These commands configure C-RP operation in the following way:

Specify the VLAN interface from which the RP IP address will be selected for advertising the router as an RP candidate.

NOTE: Only one VLAN on the router can be configured for this purpose at any time.
Enable the router as an RP candidate.

Specify the multicast groups for which the router is a CRP. (Default: Disabled.)


	NOTE: When executed without specifying a multicast group or range of groups, the resulting RP candidate defaults to allow support for all multicast groups — 224.0.0.0, 240.0.0.0, or 224.0.0.0/4.

Additionally, the following commands may be required:

To later add to or change multicast groups, or to delete multicast groups, use the command rp-candidate group-prefix [group-addr | group-mask].
To disable C-RP operation without removing the current CRP configuration, use the command no rp-candidate.
The no form of these commands:
- Deletes the RP source IP VLAN configuration.
- Deletes the multicast group assignments configured on the router for this RP.
- Disables the router from being an RP candidate.

The <vid> command identifies the VLAN source of the IP address to advertise as the RP candidate address for the router.

The command group-prefix [group-addr/mask] specifies the multicast group(s) to advertise as supported by the RP candidate. Use this option when you want to enable the C-RP and simultaneously configure it to support a subset of multicast addresses or ranges of addresses instead of all possible multicast addresses.

A group prefix can specify all multicast groups (224.0.0.0 to 239.255.255.255), a range (subset) of groups, or a single group. A given address is defined by its nonzero octets and mask. The mask is applied from the high end (leftmost) bits of the address and must extend to the last nonzero bit in the lowest-order, nonzero octet. Any intervening zero or nonzero octet requires eight mask bits. Following are examples.

228.0.0.64/26:

Defines a multicast address range of 228.0.0.64 through 228.0.0.127. (The last six bits of the rightmost octet are wildcards.)

228.0.0.64/30:

Defines a multicast address range of 228.0.0.64 through 228.0.0.67. (The last two bits of the rightmost octet are wildcards.)

228.0.0.64/32:

Defines a single multicast address of 228.0.0.64. (There are no wildcards in this group prefix.)

228.0.0.64/25:

Creates an error condition caused by the mask failing to include the last (rightmost) nonzero bit in the lowest-order, nonzero octet. (That is, this mask supports an address of 228.0.0.128, but not 228.0.0.64.)


	NOTE: The larger the mask, the smaller the range of multicast addresses supported. A mask of 32 bits always specifies a single multicast address. For example 230.0.15.240/32 defines a single multicast address of 230.0.15.240.

Enabling or disabling C-RP operation

Use this command when the router is already configured with a source IP VLAN ID and you want to enable or disable C-RP operation on the router.

Syntax:

[no]rp-candidate

Enables C-RP operation on the router. Requires that the source IP VLAN is currently configured, but disabled.

The no form of the command disables the currently configured C-RP operation, but does not change the configured C-RP settings.

Adding or deleting a multicast group address

Use this command if you need to modify the multicast address group configuration for a C-RP on the router.

Syntax:

[no]rp-candidate group-prefix [ group-addr | group-mask ]

Adds a multicast group address to the current C-RP configuration. Requires that the source IP VLAN (See Specifying the source IP VLAN (optionally configuring multicast groups or range of groups)) is already configured. The no form of the command removes a multicast group address from the current C-RP configuration.

This command does not enable or disable RP candidate operation.

NOTE: An RP candidate supports up to four separate multicast address groups. If only one group-prefix address exists in the router PIM configuration, you cannot delete it unless you first add another group-prefix address.

Changing the C-RP hold-time

Hold-time is included in the advertisements the C-RP periodically sends to the domain's elected BSR, and updates the BSR on how long to wait after the last advertisement from the reporting RP before assuming that it has become unavailable.

Syntax:

rp-candidate hold-time [30-255]

Changes the hold time a C-RP includes in its advertisements to the BSR. Also, if C-RP is configured, but disabled, this command re-enables it.

(Default: 150 seconds; Range: 30–255 seconds.)

Changing a C-RP's election priority

This priority is significant when multiple C-RPs in a given domain are configured to support one or more of the same multicast groups.

Syntax:

rp-candidate priority [0-255]

Changes the current priority setting for a C-RP. Where multiple C-RPs are configured to support the same multicast group(s), the candidate having the highest priority is elected. Zero (0) is the highest priority, and 255 is the lowest priority.

(Default: 192)

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	NOTE: Only one VLAN on the router can be configured for this purpose at any time.


	NOTE: An RP candidate supports up to four separate multicast address groups. If only one group-prefix address exists in the router PIM configuration, you cannot delete it unless you first add another group-prefix address.