R3166-R3206-HP High-End Firewalls Network Management Configuration Guide-6PW101

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To do... Use the command... Remarks
Configure C-RP timeout time c-rp holdtime interval
Optional
150 seconds by default
NOTE:
For 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.
1. 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 needs to be made on all routers in the PIM-SM domain. The following are typical BSR
spoofing cases and the corresponding preventive measures:
• 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.
• 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. As 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.
The above-mentioned preventive measures can partially protect the security of BSRs in a network.
However, if a legal BSR is controlled by an attacker, the above-mentioned problem will still occur.
Follow these steps to configure a C-BSR:
To do... Use the command... Remarks
Enter system view system-view —
Enter public instance pim —