hsrp election

[sarahr202]

Hi everybody.

My book says (with regard to hrsp) the router with the highest priority assumes active role while the router with  the second highest priority assumes standby role.

If there is a tie, the router with highest ip address becomes active while the router with second highest ip becomes standby.

I Setup a lab to put the above concept to test. 

R1----------layer2sw-----------------R2

R1 199.199.199.1

R2 199.199.199.2

The priority is left to default setting i.e  100

First ,I turn on R1 and let it wins the election. Once R1 assumes " active " role, I turn on R2. R2 assumes as expected " standby" role.

The output below indicates that:

R2#show standby

FastEthernet0/0 - Group 1

  State is Standby

    1 state change, last state change 00:00:05

  Virtual IP address is 199.199.199.10

  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

    Next hello sent in 0.776 secs

  Preemption disabled

  Active router is 199.199.199.1, priority 100 (expires in 8.932 sec)

  Standby router is local

  Priority 100 (default 100)

  Group name is "hsrp-Fa0/0-1" (default)

Next I configure R2 with " standby 1 preempt", hoping R2 will eventualy  assume " active" role. But R2 did not do so. My understanding was R2 should have assumed " active role" having been configured with " standby 1 preempt" because it has the higher ip address 199.199.199.2 than the current  active router's 199.199.199.1

R2 remains " standy" inspite of being configured with "  standby 1 preempt".

The output below indicates that:

R2#show standby

FastEthernet0/0 - Group 1

  State is Standby

    1 state change, last state change 00:02:31

  Virtual IP address is 199.199.199.10

  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

    Next hello sent in 1.728 secs

  Preemption enabled

  Active router is 199.199.199.1, priority 100 (expires in 9.984 sec)

  Standby router is local

  Priority 100 (default 100)

  Group name is "hsrp-Fa0/0-1" (default)

my question is Why?

Is it because the concept of using ip address as a tie breaker when the priorities are equal only applies when the routers initializes for hrsp operation at the same time?

thanks and have a nice weekend.

[cflory · Accepted solution]

Yes, I believe you are correct, it is only for the election period.  After that, all things being equal, the standby router won't preempt unless it sees a lower priority from it's primary (either during a router down period, or a tracked interface - decrements value by 10).

If you need R2 to be primary, you could power on R2 first, and then R1.

HTH!

-Chris

[Kishore Chennupati · Accepted solution]

hi sarah,

Yes, what you see is normal operation of HSRP. Once a device comes up and assumes Active role and then you bring another device into the group and increase its priority , it will  takeover the Active role. This is ideal to avoid any unnecessary outages etc. if you like to make the other router Active then simply shut the interface and un shut it and it will become Active.No need to actually reboot the other router.

HTH

Kishore

[Peter Paluch · Accepted solution]

Hello Sarah,

Please allow me to join the two gentlemen who already covered this issue very nicely

Next I configure R2 with " standby 1 preempt", hoping R2 will eventualy   assume " active" role. But R2 did not do so. My understanding was R2  should have assumed " active role" having been configured with " standby  1 preempt" because it has the higher ip address 199.199.199.2 than the  current  active router's 199.199.199.1

If R2 had a higher priority than R1, it would certainly assume the Active role. However, if the current Active and Standby have the same priority even though the Standby has a higher IP address, it will not preempt the current Active router even if configured with preemption. This is quite directly stated in the FHRP Configuration Guide at

http://www.cisco.com/en/US/docs/ios-xml/ios/ipapp_fhrp/configuration/15-0m/fhp-hsrp.html#GUID-1B905648-DF2B-4B68-9821-594EA794A176

A standby router with equal priority but a higher IP address will not preempt the active router.

I believe that this is logical. You are using HSRP priorities to declare which router is the preferred gateway if multiple routers are running. However, if two routers have the same priority then from the viewpoint of your configuration, you are considering them to be equal. In that case, it does not make sense to introduce transient instability into your network by the Standby router assuming the Active role just because of its higher IP address (which can be considered in this context just a coincidence).

Best regards,

Peter

[Kishore Chennupati · Accepted solution]

Peter,

I just read my post again and saw that I wasn't really giving much explanation . I should have quoted some cisco links etc so that its provides more information. I should be more descriptive in my posts. but oh well..sometimes less is more. bahaha

Regards, Kishore