H3C Technologies H3C SecPath F1000-E - Manual (Page 116)

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To do... Use the command... Remarks
Enter system view system-view —
Enter public network PIM view pim —
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 PIM-SM, see Configuring PIM
Common Timers .
Configuring a BSR
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 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 summarized as
follows:
• Initially, every C-BSR assumes itself to be the BSR of this PIM-SM 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 there is
a tie 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, while 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 PIM-SM 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
entire network, all these routers will discard bootstrap messages from out of the legal address
range.