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!