Page 358

318

Chapter 8

Hot Standby Routing Protocol (HSRP)

HSRP Tracking

The next problem addressed by HSRP is the failing of other interfaces
besides the one running HSRP. In the example shown in Figure 8.3, for
instance, if Router B's WAN connection should fail, you would want Router
A to become the active router. You can accomplish this by HSRP tracking.

You can configure Router B so that if the WAN interface fails, Router B

will reduce its priority by a set amount. The default amount is 10. Take a
look at this sample to see how it is done:

RouterB#conf t

RouterB(config)#int ethernet 0

RouterB(config-if)#standby 1 track serial 0 50

RouterB(config-if)#exit

RouterB(config)#int serial 0

RouterB(config-if)#shutdown

%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0,
changed state to down

SB1: Ethernet0 Priority was 110 now 60, configured as 110

SB1:Ethernet0 Hello out 10.1.0.2 Active pri 60 hel 3 hol
10 ip 10.1.0.200

SB1:Ethernet0 Coup in 10.1.0.1 Standby pri 100 hel 3 hol
10 ip 10.1.0.200

18:01:37: %STANDBY-6-STATECHANGE: Standby: 1: Ethernet0
state Active -> Speak

SB1:Ethernet0 Resign out 10.1.0.2 Speak pri 60 hel 3 hol
10 ip 10.1.0.200

SB1:Ethernet0 Hello out 10.1.0.2 Speak pri 60 hel 3 hol 10
ip 10.1.0.200

SB1:Ethernet0 Hello in 10.1.0.1 Active pri 100 hel 3 hol
10 ip 10.1.0.200

Let's consider what happened in the preceding sample. Router B was con-

figured to track interface serial 0. If interface serial 0 goes down, then Router B
should reduce the standby priority by 50. When serial 0 is shut down, the pri-
ority drops from 110 to 60. Router A, which must be configured to Preempt,
becomes the active router (a coup) because it has a priority of 100. As you
can see in the following output, Router B is now the standby router:

RouterB#show standby

Ethernet0 - Group 1

Local state is Standby, priority 60, may preempt

www.sybex.com