H3C Technologies H3C S10500 Series Switches - Manual (Page 177)

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Follow these steps to configure C-RP timers globally:
To do... Use the command... Remarks
Enter system view system-view —
Enter public network PIM view or
VPN instance PIM view pim [ vpn-instance
vpn-instance-name ]
—
Configure the C-RP-Adv interval c-rp advertisement-interval interval
Optional
60 seconds by default
Configure C-RP timeout time c-rp holdtime interval
Optional
150 seconds by default
NOTE:
For more information about the configuration of other timers in BIDIR-PIM, see “ Configuring PIM common
timers .”
Configuring a BSR
A BIDIR-PIM 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 collects and advertises RP information in the
BIDIR-PIM domain.
Configuring a C-BSR
C-BSRs must be configured on routers in the backbone network. When configuring a router as a C-BSR,
be sure to specify a PIM-SM-enabled interface on the router. The BSR election process is as follows:
• Initially, every C-BSR assumes itself to be the BSR of the BIDIR-PIM domain, and uses its interface IP
address as the BSR address to send bootstrap messages.
• When a C-BSR receives the bootstrap message of another C-BSR, it first compares its own priority
with the other C-BSR’s priority carried in message. The C-BSR with a higher priority wins. 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 assumes itself to be the BSR, and the winner
retains its own BSR address and continues assuming itself to be the BSR.
Configuring a legal range of BSR addresses enables filtering of bootstrap messages based on the
address range, thus to prevent a maliciously configured host from masquerading as a BSR. The same
configuration must be made on all routers in the BIDIR-PIM domain. The following are typical BSR
spoofing cases and the corresponding preventive measures:
1. Some maliciously configured hosts can forge bootstrap messages to fool routers and change RP
mappings. Such attacks often occur on border routers. Because a BSR is inside the network
whereas hosts are outside the network, you can protect a BSR against attacks from external hosts
by enabling the border routers to perform neighbor checks and RPF checks on bootstrap messages
and discard unwanted messages.
2. When a router in the network is controlled by an attacker or when an illegal router is present in the
network, the attacker can configure this router as a C-BSR and make it win BSR election to control
the right of advertising RP information in the network. After being configured as a C-BSR, a router
automatically floods the network with bootstrap messages. Because a bootstrap message has a
TTL value of 1, the whole network will not be affected as long as the neighbor router discards these
bootstrap messages. Therefore, with a legal BSR address range configured on all routers in the