Cisco’s Hot Standby Routing Protocol (HSRP) provides Workstations with a backup router in case it’s default gateway goes down. HSRP creates a virtual router with a virtual MAC address and a Virtual IP address.
Many lectures suggest that Windows has this feature. While it is true that we can add multiple default gateways this feature is only used at boot up time. In other words the host will ARP for the first default gateway on the list if that ARP fails it will continue down the list.
What happens when the host has successfully found the default gateway and it subsequently dies?
The host will need to be re-booted!
HSRP solves this problem because it is dynamic if the primary router dies the secondary will take over and the host will never know the difference.
Let’s take a look at the following scenario.
version 11.3 no service password-encryption ! hostname Router_A ! enable secret 5 $1$.s1R$iaEqZxLnYJo2QlZi8UNaO0 enable password ! interface Ethernet0/0 ip address 10.0.0.1 255.0.0.0 no ip redirects standby 1 priority 110 standby 1 preempt standby 1 ip 10.0.0.3 ! interface Serial0/0 ip address 150.10.0.1 255.255.0.0 no ip mroute-cache ! interface TokenRing0/0 no ip address shutdown ring-speed 16 ! interface FastEthernet1/0 no ip address shutdown ! router igrp 100 network 10.0.0.0 network 150.10.0.0 ! ip classless no logging buffered ! ! line con 0 exec-timeout 0 0 line aux 0 line vty 0 4 login ! end
Configuration for Router_B
Current configuration: ! version 11.2 ! hostname Router_B ! ! ! interface Ethernet0 ip address 10.0.0.2 255.0.0.0 no ip redirects standby 1 preempt standby 1 ip 10.0.0.3 ! interface Ethernet1 no ip address shutdown ! interface Serial0 ip address 192.20.30.1 255.255.255.0 ! interface Serial1 no ip address shutdown ! router igrp 100 network 10.0.0.0 network 192.20.30.0 ! no ip classless5/27/98 ! ! line con 0 line aux 0 line vty 0 4 login ! end
Configuration for Workstation A
The following is the result of putting the e0/0 interface in “shut” mode.
Router_A(config)#int e0/0 Router_A(config-if)#shut Router_A(config-if)# %STANDBY-6-STATECHANGE: Standby: 1: Ethernet0/0 state Active -> Init %LINK-5-CHANGED: Interface Ethernet0/0,changed state to administratively down
The following is the result of putting the e0/0 interface in “no shut” mode.
Router_A(config-if)#no shut Router_A(config-if)# %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet0/0, changed state to up %LINK-3-UPDOWN: Interface Ethernet0/0, changed state to up %STANDBY-6-STATECHANGE: Standby: 1: Ethernet0/0 state Listen - Active
The following is the result of a successful ping from workstation A
Router_B#debug ip icmp ICMP packet debugging is on Router_B# ICMP: echo reply sent, src 10.0.0.3, dst 10.0.0.4 ICMP: echo reply sent, src 10.0.0.3, dst 10.0.0.4 ICMP: echo reply sent, src 10.0.0.3, dst 10.0.0.4