H3C Technologies H3C S10500 Series Switches - Manual (Page 404)

389
• 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:
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
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.
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.
Follow these steps to configure a C-BSR:
To do… Use the command… Remarks
Enter system view system-view —
Enter IPv6 PIM view pim ipv6 —
Configure an interface as a
C-BSR c-bsr ipv6-address
[ hash-length [ priority ] ] Required
No C-BSRs are configured by default.
Configure a legal BSR
address range
bsr-policy acl6-number
Optional
No restrictions on BSR address range by default
NOTE:
Because a large amount of information will be 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.
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.