PIM-SM Version 2 RP Selection

PIM-SM Version 2 RP Selection

One or more BSRs need to be configured in the domain using the global configuration command:

ip pim bsr-candidate interface-type interface-number hash-mask-length [priority]

interface-type interface-number

The address of the specified interface will be used to identify the BSR.

hash-mask-length

Length of the mask (32 bits maximum) that is ANDed with the group address before the hash function is called. All groups with the same seed correspond to the same RP. If the value is 24, then only the first 24 bits of the group address are used. Therefore, one RP can have multiple groups.

priority

Optional. Value from 0 to 255. The BSR candidate with the largest priority is preferred. If BSR candidates have the same priority, the one with the highest IP address is elected as the BSR.

This command causes the router to send Bootstrap messages to PIM neighbors. When a Bootstrap message is received, the priority and address of the message are compared to the previous message. If they are the same, then the message is forwarded. If the received message has a lower priority, or if the priority is the same but the IP address is lower, the message is discarded. Otherwise, the address and priority are cached and the message is forwarded.

After the bootstrap router(s) are configured, then the RP routers are configured using the global command:

ip pim rp-candidate interface-type interface-number [group-list access-list-number]

The address of the specified interface will be used to identify the candidate RP.

Optional. Standard IP access list used to determine the groups that the candidate RP advertises

To configure a candidate RP that will advertise any multicast group starting with 227, the following command can be used:

ip pim rp-candidate serial 1 group-list 51

access-list 51 permit 227.0.0.0 0.255.255.255

The PIM-SM domain can be divided into BSR subdomains with their own configured BSRs. If you do not want BSR messages to cross domains, use the interface configuration command

ip pim border

When this command is used, no Bootstrap messages can pass through the router in either direction, but other PIM messages can pass through the router.

By default, a router will accept all Join and Prune messages. A router can be configured to accept Joins or Prunes for specified groups for a specified RP. The command used to accomplish this filtering is the global command:

ip pim accept-rp {address | auto-rp} [access-list-number]

address

Address of the RP.

auto-rp

Messages are accepted only for RPs that are in the Auto-RP cache.

access-list-number

Optional. Defines the groups that are allowed.

This command causes the router to accept only Join and Prune messages destined for the specified RP. If an access list is used, then the group must also be allowed by the list. If the address in the command is an address on the receiving router, then the router is the RP and it will accept messages only for the groups specified. If the group is not allowed by the access list, then the router will respond immediately to Register messages with Register-Stop messages. For example, to configure a router to accept Join and Prune messages for the RP whose ID is 172.16.1.1 related to groups 225.0.0.0 through 225.255.255.255, use the command

ip pim accept-rp 172.16.1.1 8

access-list 8 permit 225.0.0.0 0.255.255.255

RP mapping agents can be configured to filter Auto-RP announcements using the global configuration command:

ip pim rp-announce-filter rp-list access-list-number group-list access-list-number

rp-list access-list-number

Standard access list of RP addresses from which Auto-RP announcements will be accepted.

group-list access-list-number

Standard access list of group addresses that will be accepted.

For example, to configure an RP mapping agent to accept Auto-RP announcements from the RP with address 172.16.1.1 for all multicast groups, use

ip pim rp-announce-filter rplist 12 group-list 13

access-list 12 permit 172.16.1.1

access-list 13 permit 224.0.0.0 15.255.255.255

The PIM version can be configured using the interface configuration command

ip pim version [1 | 2]

If an interface is configured for version 2 (the default) and a PIM version 1 neighbor is discovered on the interface, then the router automatically switches to PIM version 1. If the PIM version 1 neighbors somehow vanish, the router switches the interface back to PIM version 2.

Figure 7-34: Example network for static RP configuration. Only the leaf routers need to be configured with the address of the RP.

be adjusted using the interface command:

ip pim query-interval seconds

seconds

1—65535 seconds

The following command changes the PIM query interval to 60 seconds:

interface Serial 0

ip pim query-interval 60

PIM-SM SPT-Switchover is controlled by the global configuration command:

ip pim spt-threshold {kbps | infinity} [group-list access-list-number]

kbps

Traffic rate in kilobits per second.

infinity

The specified groups will use the shared-tree.

group-list access-list-number

Optional. Determines which groups to apply the threshold.

By default, a PIM-SM router sends periodic Join/Prune messages every 60 seconds. To alter this interval, use the global configuration command

ip pim message-interval seconds

seconds

Value in the range 1 to 65535

All PIM-SM-enabled routers should be configured with the same message interval time. A router will be pruned from a group if a Join message is not received in the message interval. The default value is three minutes.