4000 Router Series IP Multicast Configuration Guide

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does not receive any advertisement message when the timer expires, it regards the C-RP failed or

unreachable.

To guard against C-RP spoofing, you must configure a legal C-RP address range and the multicast group

range to which the C-RP is designated. In addition, because every C-BSR might become the BSR, you

must configure the same filtering policy on all C-BSRs in the PIM-SM domain.

To configure a C-RP:

Ste

Command

Remarks

1. Enter system view.

system-view

N/A

2. Enter PIM view.

pim [ vpn-instance vpn-instance-name ]

N/A

3. Configure a C-RP.

c-rp ip-address [ advertisement-interval

adv-interval | group-policy acl-number

| holdtime hold-time | priority priority ]

By default, no C-RP is

configured.

4. (Optional.) Configure a legal

C-RP address range and the

multicast group range to

which the C-RP is designated.

crp-policy acl-number

By default, no restrictions are

defined.

Configuring a BSR

You must configure a BSR if C-RPs are configured to dynamically select the RP. In a network with a static

RP, this configuration task is unnecessary.

A PIM-SM domain can have only one BSR, but must have at least one C-BSR. Any router can be

configured as a C-BSR. Elected from C-BSRs, the BSR is responsible for collecting and advertising RP

information in the PIM-SM domain.

Configuring a C-BSR

C-BSRs should be configured on routers on the backbone network. The BSR election process is

summarized as follows:

• Initially, each C-BSR regards itself as the BSR of the PIM-SM domain and sends BSMs to other

routers in the domain.

• When a C-BSR receives the BSM from another C-BSR, it compares its own priority with the priority

carried in the message. The C-BSR with a higher priority wins the BSR election. If a tie exists in the

priority, the C-BSR with a higher IP address wins. The loser uses the winner's BSR address to replace

its own BSR address and no longer regards itself as the BSR, and the winner retains its own BSR

address and continues to regard itself as the BSR.

In a PIM-SM domain, the BSR collects C-RP information from the received advertisement messages from

the C-RPs, encapsulates the C-RP information in the RP-set information, and distributes the RP-set

information to all routers in the PIM-SM domain. All routers use the same hash algorithm to get an RP for

a specific multicast group.

Configuring a legal BSR address range enables filtering of BSMs based on the address range, thereby

preventing a maliciously configured host from masquerading as a BSR. The same configuration must be

made on all routers in the PIM-SM domain. The following describes the typical BSR spoofing cases and

the corresponding preventive measures: