Operation Manual – Multicast Protocol
H3C S3610&S5510 Series Ethernet Switches
Chapter 6 PIM Configuration
6-21
6.3.4 Configuring a BSR
Note:
The BSR is dynamically elected from a number of C-BSRs. Because it is unpredictable
which router will finally win a BSR election, the commands introduced in this section
must be configured on all C-BSRs.
About the Hash mask length and C-BSR priority for RP selection calculation:
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You can configure these parameters at three levels: global configuration level,
global scope level, and BSR admin-scope level.
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By default, the global scope parameters and BSR admin-scope parameters are
those configured at the global configuration level.
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Parameters configured at the global scope level or BSR admin-scope level have
higher priority than those configured at the global configuration level.
I. Performing basic C-BSR configuration
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, a BSR is responsible for
collecting and advertising RP information in the PIM-SM.
C-BSRs should be configured on routers in the backbone network. When configuring a
router as a C-BSR, make sure that router is PIM-SM enabled. The BSR election
process is as follows:
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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.
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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 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
keeps its own BSR address and continues assuming itself to be the BSR.
Configuring a legal range of BSR addresses enables filtering of BSR messages based
on the address range, thus to prevent malicious hosts from initiating attacks by
disguising themselves as legitimate BSRs. To protect legitimate BSRs from being
maliciously replaced, preventive measures are taken specific to the following two
situations:
1)
Some malicious hosts intend to fool routers by forging BSR messages and change
the RP mapping relationship. 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 border routers to
