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Configuring a C-BSR
C-BSRs must be configured on routers on the backbone network. When configuring a router as a
C-BSR, be sure to specify an IPv6 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 IPv6 BIDIR-PIM domain, and uses its
interface IPv6 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 IPv6 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 IPv6 BIDIR-PIM 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 an attacker controls a router on the network, the attacker can configure the router as a
C-BSR to win the BSR election. Through this router, the attacker controls the advertising of RP
information. For security purposes, you can configure a legal BSR address range on all routers
on the network. Therefore, all routers can discard BSMs that are out of the legal address range.
The preventive measures can partially protect the security of BSRs in a network. However, if a legal
BSR is controlled by an attacker, the preceding problem will still occur.
Because a large amount of information is exchanged between a BSR and the other devices in the
IPv6 BIDIR-PIM domain, a relatively large bandwidth should be provided between the C-BSRs and
the other devices in the IPv6 BIDIR-PIM domain.
To configure a C-BSR:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter IPv6 PIM view.
pim ipv6
N/A
3.
Configure an interface as a
C-BSR.
c-bsr
ipv6-address
[
hash-length
[
priority
] ]
No C-BSRs are configured by
default.
4.
Configure a legal BSR
address range.
bsr-policy
acl6-number
Optional.
No restrictions on BSR address
range by default.
Configuring an IPv6 BIDIR-PIM domain border
As the administrative core of an IPv6 BIDIR-PIM domain, the BSR sends the collected RP-Set
information in the form of bootstrap messages to all routers in the IPv6 BIDIR-PIM domain.
An IPv6 BIDIR-PIM domain border is a bootstrap message boundary. Each BSR has its specific
service scope. A number of IPv6 BIDIR-PIM domain border interfaces partition a network into
different IPv6 BIDIR-PIM domains. Bootstrap messages cannot cross a domain border in either
direction.
Perform the following configuration on routers that you want to configure as the IPv6 BIDIR-PIM
domain border.
