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Configuring a BSR
An IPv6 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 IPv6 PIM-SM domain.
Configuring a C-BSR
You should configure C-BSRs on routers in the backbone network. When you configure a router as a
C-BSR, be sure to specify the IPv6 address of 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 this IPv6 PIM-SM 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 the 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
keeps its own BSR address and continues to assume itself to be the BSR.
Configuring a legal range of BSR addresses enables filtering of bootstrap messages based on the
address range, thereby preventing a maliciously configured host from masquerading as a BSR. You must
make the same configuration on all routers in the IPv6 PIM-SM domain. The following describes the
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 to
discard unwanted messages.
•
If an attacker controls a router in the network or if the network contains an illegal router, 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 you configure a router as a C-BSR, the router automatically
floods the network with bootstrap messages. Because a bootstrap message has a hop limit 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.
These preventive measures can partially protect the security of BSRs in a network. However, if an attacker
controls a legal BSR, the problem still exists.
Because the BSR and the other devices exchange a large amount of information in the IPv6 PIM-SM
domain, provide a relatively large bandwidth between the C-BSRs and the other devices.
To complete basic BSR configuration:
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 by default.
