You’ve got two Cisco routers, and two links to a remote site. How do you make your hosts use the backup when needed? One method is HSRP.
HSRP stands for Hot Standby Router Protocol, and what it does is create a virtual IP address (which hosts will use as the gateway address). This virtual address is free to move between configured routers as needed.
Some background for this config:
Local Subnet: 192.168.2.0/24
Desired gateway address: 192.168.2.1
Both routers and their hosts must be on the same layer 2 network.
On Router A:
ip address 192.168.2.2 255.255.255.0
standby 1 ip 192.168.2.1
standby 1 preempt
standby 1 priority 110
standby 1 authentication myrouter
standby 1 track serial 0/0
The priority number determines which router will normally have the virtual IP address, higher numbers win.
The track statement tells the router to give up the virtual address if the serial 0/0 interface goes down.
Router B:
ip address 192.168.2.3 255.255.255.0
standby 1 ip 192.168.2.1
standby 1 preempt
standby 1 priority 100
standby 1 authentication myrouter
standby 1 track serial 0/1
That’s all there is to it! Router A will host the virtual IP address, and if the router or it’s serial port goes down, Router B will assume control of the virtual address, and traffic will flow over it’s serial link.
