HSRP Configuration Advice

[bjenner]

I currently have two sites connected by a 100Mb ethernet link with a 2Mb serial backup. At either end I have a 2600 routers running eigrp although most routes are statically enter at either end and redistributed with eigrp.

I have recently acquired another 2 2600 routers and was thinking of adding them to increase resilience. My plan was to leave the existing routers with the 100Mb link and set-up the other 2 routers with HSRP and the 2Mb link.

My 1st question is if the 100MB link failed would traffic be routed over the 2MB link or does the primary router need to physically fail before the switch would happen.

My second question is linked to the first, which is do I need to repeat all the static routes on the standby routers and make them part of the same eigrp group.

My objective is to provide the best resilience in terms of backup routers and Wide area links. Can anybody advise?

Thanks.

[konigl]

Answer to your 1st question:

Yes, HSRP can be configured such that if the 100-meg link fails in your stated design then the traffic can be routed through the 2-meg serial link instead. You would use the "standby preempt" and "standby track" commands to accomplish this.

Basically, you would configure HSRP on the LAN interface to track the state of the 100-meg outbound interface, decreasing the HSRP priority of the LAN interface by an amount sufficient to cause the standby router to go active when the 100-meg link fails. The standby router (the one with the 2-meg serial) would have HSRP "standby preempt" configured on its LAN interface to allow it to take over from an active HSRP router if the standby router's priority is higher. See this link for details:

How to Use the standby preempt and standby track Commands

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094e8c.shtml

Answer to your 2nd question:

I don't know why you have all those static routes if you're using EIGRP (probably would need to know more about your network to understand better) but I imagine you'd have to configure the same route information on each router so that it would know how to reach the remote subnets. Just be sure that the next-hop IP address you specify for each subnet is appropriate for the particular router you're putting the static routes on.

Your users on each of the LANs will use the HSRP virtual or shared IP address as default gateway. Once they toss the IP traffic to the active HSRP router, it's up to EIGRP and the static routes to find the best way to get the traffic to its destination.

Hope this helps.

EDITED TO ADD: I forgot to say, you don't need to physically fail the active router for the standby router to go active.

[bjenner]

Many Thanks for you information. I did discover the document you suggested I read last night, but it good to have something confirmed. This is a new job I've just started but even though I agree with your comments about the use of static routes and eigrp the network is functional so for the time being I'm leaving it that way.

Thanks again.

Bill