IP routing between two Cisco router

Unanswered Question
Jan 11th, 2008

We have two cisco routers 2821 and 3845. They both have same LAN subnets and are interconnected. However, both these units route to the internet thru two different ISPs. My question is: how can we set up the 3845 (main router) to failover to the 3821? Meaning that if the cisco 3845 WAN connection (ISP1) fails, then all internet requests will be rerouted to ISP2 on cisco 3821.

I have this problem too.
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Edison Ortiz Fri, 01/11/2008 - 14:59

You can setup HSRP on the LAN interfaces (the interfaces sharing the internal subnet).

Configure the clients to point to the HSRP address instead of the physical LAN interface on the respective router.

Under the HSRP configuration, you can add the tracking option.

With tracking, you can set up an IP SLA to track reachability to an internet route. If the internet route is down, the HSRP option will deactive the router as primary.

Please understand HSRP by reading:


and object tracking:





bizisam20045 Fri, 01/11/2008 - 15:35

Good advice. I believe that HSRP would be the best way to go. It works same way as VRRP feature set on other branded routers. But in our case, we would like to have both routers active and accessing the internet at the same time thru both ISPs. Could that be possible?

jwdoherty Fri, 01/11/2008 - 16:54

Outbound (to the Internet), if the IOS is new enough, you could use GLBP instead of HSRP.

Inbound (from the Internet), is harder to control. Much would depend on whether you have our own public AS and whether your ISP might be willing to cooperate with you.


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