HSRP Priority

[navneet_78]

I have seen in many routers the Priority in Active Routers being 115 and 100 in the Standby one. Is there any reason for having diff priority values? Also Suppose A device has 110 as priority and B has default 100. If i want to make B active should i make B as 115 or make A as 95, as both will work.

[ankurbhasin]

Hi Navneet,

Priority is HSRP confiuration is used to decide which router should be active and which router should be standby. Bydefault the HSRP priority is 100 for all the cisco routers and layer switches.

If you want to make some router as active you have to configure priority more than 100 like 110 or 115 and the maximum is 255.

Also there is a other way round if you just reduce the priority of box which you want to be standby to 90 for suppose the other box will have the default priority of 100 will be active.

So priority decide which router should be active and standby.Even if you do not assign any priority value and left the value be default 100 for both the routers the active and standby routers are decided by ip addresses.

As per the question even if you make A as 95 your B will become active cause it has a default of 100 and vice versa. BUt I will always recommend you to change the priority other then default value which is 100 cause sometime cisco IOS behave wierd on default values.

Hope that helps - pls rate the post if it does.

Ankur

[pkhatri]

Hi Navneet,

The HSRP priority value difference is quite important when you are using interface tracking. When you are tracking interfaces, the HSRP priority of a router will be reduced if a tracked interface goes down. Therefore, the difference in priority between the active and standby has to be carefully chosen ....

An example:

- A is a router with priority 110 and B with priority 105

- A has a tracked interface with the default decrement priority of 10

- when this tracked interface goes down, A's HSRP priority will become 100 and B will become active.

- if A's priority had been 120, this would have been reduced to 110 and A would have remained active

This feature is useful when you have multiple tracked interfaces so you can allow for multiple interfaces to go down before switching to the standby.

Hope that helps - pls rate the post if it does.

Paresh

[navneet_78]

Thanx for the response.

So you mean let the standby router always have the priority of 100 and active be 105. Because I have seen people jus changing the priority of the active to be less than the standby for failover to happen.

[thisisshanky]

I would change the priority on one box rather than two. So you always have a base reference priority of 100 on the standby box and just change the active box'es priority to 110 (say). As far as interface tracking feature goes, you can always set your track decrement priority to say 15 (which drops the active priority to 95, mean while keeping the standby still at 100).

HTH

[pkhatri]

Hi Navneet,

It does not really matter which way you do this. Just make sure that you don't reduce the priority to something that will result in a negative value when the priority decrement is applied.

Hope that helps - pls rate the post if it does.

Paresh