HP 6125G HP 6125G & 6125G/XG Blade Switches IP Multicast Configuration - Page 317

4. 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 assuming itself to be the BSR. • BSR legal address against BSR spoofing 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. Typical BSR spoofing cases and the corresponding preventive measures are as follows: • 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 will still occur. IMPORTANT: Because a large amount of information needs to be exchanged between a BSR and the other devices in the IPv6 PIM-SM domain, a relatively large bandwidth should be provided between the C-BSR and the other devices in the IPv6 PIM-SM domain. To configure a C-BSR: Step 1. Enter system view. 2. Enter IPv6 PIM view. 3. Configure an interface as a C-BSR. 4. Configure a legal BSR address range. Command system-view pim ipv6 c-bsr ipv6-address [ hash-length [ priority ] ] bsr-policy acl6-number Remarks N/A N/A No C-BSRs are configured by default. Optional. No restrictions by default. Configuring an IPv6 PIM domain border As the administrative core of an IPv6 PIM-SM domain, the BSR sends the collected RP-set information in the form of bootstrap messages to all routers in the IPv6 PIM-SM domain. An IPv6 PIM domain border is a bootstrap message boundary. Each BSR has its specific service scope. IPv6 PIM domain border interfaces partition a network into different IPv6 PIM-SM domains. Bootstrap messages cannot cross a domain border in either direction. 306