141
Configuring C-RP timers globally
To enable the BSR to distribute the RP-set information within the PIM-SM domain, C-RPs must
periodically send C-RP-Adv messages to the BSR. The BSR learns the RP-set information from the
received messages, and encapsulates its own IP address together with the RP-set information in its
bootstrap messages. The BSR then floods the bootstrap messages to all PIM routers in the network.
Each C-RP encapsulates a timeout value in its C-RP-Adv messages. After receiving a C-RP-Adv
message, the BSR obtains this timeout value and starts a C-RP timeout timer. If the BSR fails to hear
a subsequent C-RP-Adv message from the C-RP when this timer times out, the BSR assumes the
C-RP to have expired or become unreachable.
The C-RP timers must be configured on C-RP routers.
To configure C-RP timers globally:
Step
Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter public network PIM
view or VPN instance PIM
view.
pim
[
vpn-instance
vpn-instance-name
]
N/A
3.
Configure the C-RP-Adv
interval.
c-rp advertisement-interval
interval
Optional.
60 seconds by default.
4.
Configure C-RP timeout
timer.
c-rp holdtime
interval
Optional.
150 seconds by default.
For more information about the configuration of other timers in PIM-SM, see "
Configuring a BSR
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, the BSR is responsible for collecting and advertising
RP information in the PIM-SM domain.
Configuring a C-BSR
C-BSRs should be configured on routers in the backbone network. When configuring a router as a
C-BSR, you must specify a PIM-SM-enabled interface on the router. The BSR election process is
summarized as follows:
•
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.
•
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 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. The winner retains its own BSR address and continues to assume itself to be the
BSR.
To prevent a maliciously configured host from masquerading as a BSR, configure a legal range of
BSR addresses enables filtering of bootstrap messages based on the address range. The same
configuration must be made on all routers in the 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. A BSR is inside the network and
