Why Is the Wrong HSRP Router Active? Priority, Preempt and Tracking

How HSRP really elects the Active router

• Priority decides - 0 to 255, default 100. Highest wins.
• Ties go to the highest IP address on the HSRP interface.
• Election only happens when there is no Active router. Whoever reaches Active first keeps the role while it is healthy.
• Preempt changes that rule. With standby <group> preempt, a router that hears a lower-priority Active router takes the role over. Preempt is off by default in HSRP.

Reading show standby brief

Real output from the engine the FigigExams scenarios run on. First, the problem - on R1, the router that should be Active:

R1#show standby brief
                     P indicates configured to preempt.
                     |
Interface   Grp  Pri  P State    Active          Standby         Virtual IP
Gi0/0       1    80   P Standby  192.168.50.3    local           192.168.50.1

R1 runs at priority 80 and sits in Standby; the Active router is 192.168.50.3 (R2). The P column says R1 is configured to preempt - it just has nothing to preempt with.

R2#show standby brief
                     P indicates configured to preempt.
                     |
Interface   Grp  Pri  P State    Active          Standby         Virtual IP
Gi0/0       1    90   P Active   local           192.168.50.2    192.168.50.1

R2 runs at 90 with preempt, so it wins and holds the role. Raise R1 above 90 - and keep preempt on it - and R1 takes over:

R1#show standby brief
                     P indicates configured to preempt.
                     |
Interface   Grp  Pri  P State    Active          Standby         Virtual IP
Gi0/0       1    110  P Active   local           192.168.50.3    192.168.50.1

For the details behind the brief view - timers, the virtual MAC, who the peers are - use show standby:

R1#show standby
GigabitEthernet0/0 - Group 1
  State is Active
  Virtual IP address is 192.168.50.1
  Active virtual MAC address is 0000.0c07.ac01
    Local virtual MAC address is 0000.0c07.ac01 (v1 default)
  Hello time 3 sec, hold time 10 sec
  Preemption enabled
  Active router is local
  Standby router is 192.168.50.3
  Priority 110 (configured 110)
  Group name is "hsrp-Gi0/0-1" (default)
  Last state change 0 minutes

The three reasons the wrong router is Active

The Init case looks like this - the group is configured, but the interface under it is down:

R1#show standby brief
                     P indicates configured to preempt.
                     |
Interface   Grp  Pri  P State    Active          Standby         Virtual IP
Gi0/0       1    110  P Init     unknown         unknown         192.168.50.1

Interface tracking: failing over when the uplink dies

HSRP only watches the LAN. If the Active router's WAN uplink fails, it stays Active and blackholes traffic unless you tell HSRP to care. Tracking lowers the priority when an object goes down:

R1(config)#track 1 interface GigabitEthernet0/1 line-protocol
R1(config-track)#exit
R1(config)#interface GigabitEthernet0/0
R1(config-if)#standby 1 priority 110
R1(config-if)#standby 1 preempt
R1(config-if)#standby 1 track 1 decrement 20

With the uplink down, R1 drops to 90. For R2 to take over, R2 needs a priority above 90 and preempt configured - tracking without preempt on the peer changes nothing.

HSRP vs VRRP

A two-minute HSRP checklist

1. show standby brief on both routers: who is Active, at what priority, with or without P.
2. Same group number and same virtual IP on both? A mismatch makes two separate groups.
3. Is the intended router's priority above the peer's - after any tracking decrement?
4. Does the intended router have preempt?
5. Any router in Init? Check the interface under the group.
6. Test from a host: ping the virtual IP, then tracert to confirm which router carries the traffic.

HSRP practice questions

Five questions in the ENCOR style, each with an explanation of why the other answers fail.