HSRP Route Tracking

I have been accustomed to tracking the WAN interface to determine the HSRP priority. However, there are more ways to use tracking in HSRP and one of those is to track a certain prefix in the routing table. This works by checking a specific route configured in "track" if it is still in the routing table. If not, it will decrease the priority according the configured decrement.

R1 and R2 are in one site. R1 is the Active HSRP route while R2 is the standby. R1 and R2 should
not be OSPF neighbors. Traffic should go to R2 once a route to 3.3.3.3/32 is lost in R1.

This is not the best way to track this scenario but just for example sake. Excuse the IP addressing scheme as well because I find it easier to know which ip is from which router just by number in the last octet. (e.g. .1 is in R1, .2 is in R2 and .3 is in R3)

The pre-configuration of the routers is found below.

R1#
interface FastEthernet0/0
ip address 10.10.20.1 255.255.255.0
duplex half
standby 1 ip 10.10.20.10
standby 1 preempt
!
interface Serial1/0
ip address 10.10.13.1 255.255.255.0
serial restart-delay 0
no fair-queue
!
interface Serial1/1
no ip address
shutdown
serial restart-delay 0
!
interface Serial1/2
no ip address
shutdown
serial restart-delay 0
!
interface Serial1/3
no ip address
shutdown
serial restart-delay 0
!
router ospf 1
log-adjacency-changes
passive-interface FastEthernet0/0
network 10.10.13.0 0.0.0.255 area 0
network 10.10.20.0 0.0.0.255 area 0

R2#
interface FastEthernet0/0
ip address 10.10.20.2 255.255.255.0
duplex half
standby 1 ip 10.10.20.10
standby 1 priority 91
standby 1 preempt
!
interface Serial1/0
ip address 10.10.23.2 255.255.255.0
serial restart-delay 0
!
interface Serial1/1
no ip address
shutdown
serial restart-delay 0
!
interface Serial1/2
no ip address
shutdown
serial restart-delay 0
!
interface Serial1/3
no ip address
shutdown
serial restart-delay 0
!
router ospf 1
log-adjacency-changes
passive-interface FastEthernet0/0
network 10.10.20.0 0.0.0.255 area 0
network 10.10.23.0 0.0.0.255 area 0

R3#
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface FastEthernet0/0
no ip address
shutdown
duplex half
!
interface Serial1/0
ip address 10.10.13.3 255.255.255.0
serial restart-delay 0
!
interface Serial1/1
no ip address
shutdown
serial restart-delay 0
!
interface Serial1/2
ip address 10.10.23.3 255.255.255.0
serial restart-delay 0
!
interface Serial1/3
no ip address
shutdown
serial restart-delay 0
!
router ospf 1
log-adjacency-changes
network 3.3.3.3 0.0.0.0 area 0
network 10.10.13.0 0.0.0.255 area 0
network 10.10.23.0 0.0.0.255 area 0

Let's configure tracking and apply it on the HSRP group of 1.

R1(config)#track 1 ip route 3.3.3.3 255.255.255.255 reachability
R1(config-track)#int fa0/0
R1(config-if)#standby 1 track 1 decrement 11

Ok, lets see how a "show track" output looks like.

R1#sh track 1
Track 1
IP route 3.3.3.3 255.255.255.255 reachability
Reachability is Up (OSPF)
1 change, last change 00:01:22
First-hop interface is Serial1/0
Tracked by:
HSRP FastEthernet0/0 1

Notice that tracking knows what routing protocol the route is learned from. It also shows how long its up, which interface and what HSRP group is using. Pretty neat huh? :) Let's remove the announcement of 3.3.3.3/32 in R3 to simulate lost of entry in the routing table.

R3(config-router)#no network 3.3.3.3 0.0.0.0 area 0

Let's see how R1 reacts to that.

R1#
*Sep  4 16:57:37.679: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial1/0 from FULL to DOWN, Neighbor Down: Dead timer expired
*Sep  4 16:57:53.679: %HSRP-5-STATECHANGE: FastEthernet0/0 Grp 1 state Active -> Speak
*Sep  4 16:58:03.675: %HSRP-5-STATECHANGE: FastEthernet0/0 Grp 1 state Speak -> Standby
*Sep  4 16:58:08.747: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial1/0 from LOADING to FULL, Loading Done
*Sep  4 16:58:23.691: %HSRP-5-STATECHANGE: FastEthernet0/0 Grp 1 state Standby -> Active
*Sep  4 16:58:38.831: %HSRP-5-STATECHANGE: FastEthernet0/0 Grp 1 state Active -> Speak
*Sep  4 16:58:48.831: %HSRP-5-STATECHANGE: FastEthernet0/0 Grp 1 state Speak -> Standby

R1#sh standby br
            P indicates configured to preempt.
            |
Interface   Grp Prio P State    Active          Standby         Virtual IP
Fa0/0       1   89   P Standby  10.10.20.2      local           10.10.20.10

R1#sh track 1
Track 1
IP route 3.3.3.3 255.255.255.255 reachability
Reachability is Down (no route)
4 changes, last change 00:00:56
First-hop interface is unknown
Tracked by:
HSRP FastEthernet0/0 1

Ok, as we can see, once OSPF detected that the network isn't anymore reachable, HSRP reacted as well by decrementing the priority by 11 as per configured. The priority is now 89, 11 less than the default HSRP priority of 100. "show track" also indicated that there is no more route going to 3.3.3.3. I would just like to point out here that if the command "standby 1 preempt" was not configured in R2, it would not assume the Active state and R1 will still remain the Active HSRP router. Preempt feature will make HSRP renegotiate.

Let's advertise again the route and see the changes.

R3(config)#router ospf 1
R3(config-router)#network 3.3.3.3 0.0.0.0 area 0

R1#sh standby br
                  P indicates configured to preempt.
                  |
Interface   Grp Prio P State    Active          Standby         Virtual IP 
Fa0/0       1   100  P Active   local           10.10.20.2      10.10.20.10

As expected R1 will reassume the HSRP Active state because the route is now found in the routing table. :)