H3C Technologies H3C S10500 Series Switches - Manual (Page 166)

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by enabling the border routers to perform neighbor checks and RPF checks on bootstrap messages
and to discard unwanted messages.
2. When an attacker controls a router in the network 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 a router is configured as a C-BSR, it
automatically floods the network with bootstrap messages. Because a bootstrap message has a
TTL 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.
Follow these steps to configure a C-BSR:
To do… Use the command… Remarks
Enter system view system-view —
Enter public network PIM view or
VPN instance PIM view pim [ vpn-instance
vpn-instance-name ]
—
Configure an interface as a C-BSR
c-bsr interface-type
interface-number [ hash-length
[ priority ] ]
Required
No C-BSRs are configured by
default.
Configure a legal BSR address
range
bsr-policy acl-number
Optional
No restrictions on BSR address
range by default.
NOTE:
•
Because a large amount of information needs to be exchanged between a BSR and the other devices in
the PIM-SM domain, a relatively large bandwidth should be provided between the C-BSRs and the other
devices in the PIM-SM domain.
• For C-BSRs interconnected via a Generic Routing Encapsulation (GRE) tunnel, multicast static routes
need to be configured to ensure that the next hop to a C-BSR is a tunnel interface. For more information
about multicast static routes, see the chapter “Multicast routing and forwarding configuration.”
Configuring a PIM domain border
As the administrative core of a PIM-SM domain, the BSR sends the collected RP-set information in the form
of bootstrap messages to all routers in the PIM-SM domain.
A PIM domain border is a bootstrap message boundary. Each BSR has its specific service scope. A
number of PIM domain border interfaces partition a network into different PIM-SM domains. Bootstrap
messages cannot cross a domain border in either direction.
Perform the following configuration on routers that you want to configure as a PIM domain border.
Follow these steps to configure a PIM domain border:
To do… Use the command… Remarks
Enter system view system-view —
Enter interface view
interface interface-type
interface-number
—