How would I set up HRSP from a core layer 3 switch to 2 routers ?

[WhiskeyHughes]

I am currently in the process of trying to revamp my COLO Cab's network design.  My goal is to have all of my VLAN Interfaces set up on a core switch and then set up routed interfaces from the core switch to 2 routers, using GLBP, VRRP, or HSRP. (Still haven't decided which one.) The reason I have decided to use only one core switch, is because no matter what, I will have a single point of failure in my network design because all of my sites are connected to our COLO by a Metro E connection, which terminates into a single connection in my cab. (Which would plug into the core switch)    

The problem I am running in to when designing this in GNS3, is when I try to set up both of the routed interfaces on the core switch, I get an error because they are on overlapping subnets. Is it even possible for this to work without setting the connections from the switch to the router as Layer 2? I really don't want to use Router on a Stick. 

Thanks!  

[Reza Sharifi · Accepted solution]

When you have routed interfaces, you can't assign the same subnet to 2 different interfaces. So what you see is the correct behavior.  You can change the /29 to 2 /30s.  This way you don't see overlapping subnets. Or make the switch layer-2 only and run HSRP between the 2 routers. Since you have 2 different ISPs, I think running HSRP between the routers with switch as layer-2 only would work fine.

HTH

[WhiskeyHughes]

Reza, 

Thanks so much for the prompt reply! So if I wanted to use two /30 connections from the switch to routers, how would I make HSRP work? Is that still a possibility, or does that rule out HSRP? 

Thanks,