Read HSRP state through a failover, a preemption and a split group

Steps

1. Drag each device from the Topology onto the workspace and set its display name (click the device, Config tab, Display Name) to the name in the Devices table. Cable the ports the Links table lists: Packet Tracer's automatic connection type picks the right cable, or use a copper cross-over between two routers or between a router and a PC or server. If a router asks whether to enter the initial configuration dialog, answer no. Name S1 at its prompt (hostname S1); it needs nothing else yet.
2. Configure R1 as the intended active router: priority 110, with preemption.

Router> enable
Router# configure terminal
Router(config)# hostname R1
R1(config)# interface g0/0/1
R1(config-if)# ip address 192.168.10.2 255.255.255.0
R1(config-if)# standby version 2
R1(config-if)# standby 10 ip 192.168.10.1
R1(config-if)# standby 10 priority 110
R1(config-if)# standby 10 preempt
R1(config-if)# no shutdown
R1(config-if)# end

3. Configure R2 with the default priority of 100 and no preemption:

Router> enable
Router# configure terminal
Router(config)# hostname R2
R2(config)# interface g0/0/1
R2(config-if)# ip address 192.168.10.3 255.255.255.0
R2(config-if)# standby version 2
R2(config-if)# standby 10 ip 192.168.10.1
R2(config-if)# no shutdown
R2(config-if)# end

Watch the console: each router logs its HSRP state changes as it moves toward Standby or Active. Whichever came up first, R1 ends Active, because it outranks R2 and preempts. 4. Give PC1 its address with the virtual IP as its gateway (Desktop > IP Configuration). Work out the virtual MAC first: HSRP version 2 is 0000.0c9f.fXXX, and group 10 is 00a in hex. Then check:

C:\> ping 192.168.10.1
C:\> arp -a

The ARP entry for 192.168.10.1 should be 0000.0c9f.f00a, not either router's own MAC. 5. Read both routers and predict each column before you look:

R1# show standby brief
R2# show standby brief
R1# show standby

R1: State Active, Active local, Standby 192.168.10.3, and a P for preempt. R2: State Standby, Active 192.168.10.2, Standby local, no P. The detailed output on R1 shows Group 10 (version 2), the virtual MAC and Hello time 3 sec, hold time 10 sec. 6. Fail the active router's LAN interface and read the result:

R1# configure terminal
R1(config)# interface g0/0/1
R1(config-if)# shutdown
R1(config-if)# do show standby brief
R2# show standby brief
C:\> ping 192.168.10.1
C:\> arp -a

R1 shows Init: the group is configured but the interface is down. R2 is Active with the standby unknown. PC1 still reaches 192.168.10.1, and its ARP entry is unchanged, because R2 took over the virtual MAC as well as the virtual IP. 7. Bring R1 back. With preemption it takes the active role back as soon as it is ready:

R1(config-if)# no shutdown
R1(config-if)# do show standby brief

8. Now see HSRP's default, no preemption. Remove it on R1 and repeat the failure:

R1(config-if)# no standby 10 preempt
R1(config-if)# shutdown
R1(config-if)# no shutdown
R1(config-if)# do show standby brief

R1 comes back as Standby at priority 110, and R2 stays Active at 100: a better priority does not take over without preemption. Put it back and watch R1 take over at once:

R1(config-if)# standby 10 preempt
R1(config-if)# end

9. Break and fix: split the group. Move R2's switch port into a different VLAN:

S1> enable
S1# configure terminal
S1(config)# vlan 20
S1(config-vlan)# exit
S1(config)# interface g0/2
S1(config-if)# switchport access vlan 20
S1(config-if)# end

After about 10 seconds, run show standby brief on both routers. Both say Active, each with the standby unknown: neither hears the other's hellos. Preemption has nothing to do with it. Look for the cause from the switch:

S1# show vlan brief

Gi0/2 is listed under VLAN 20 while Gi0/1 and Fa0/1 are in VLAN 1. Fix it, and R2 drops back to Standby once it hears R1's higher priority:

S1# configure terminal
S1(config)# interface g0/2
S1(config-if)# switchport access vlan 1
S1(config-if)# end