I'm connecting a Cisco 2851 router to a Layer 3 3750-X stack (2 switches). The Gi0/0 interface connects to an access port on the stack master.

How can I achieve redundancy from the 2851 to the stack member? Throw another HWIC into the router and connect to the stack member? Or is there not an option

I'm using EIGRP between this location (2851) and our headquarters (2851).

2 Answers 2


The other option is to use the second physical interface as a second subnet and let eigrp from a second neighbor relationship. If the speeds are the same you can do equal cost load balancing. Finally 2 separate L3 links are easier to troubleshoot than a port channel and you don't have to have the exact same hardware. Its a matter of style. I am assuming you are running eigrp between the switch and the router. If you are not then 2 static default routes will do the routing trick.

  • Correct, I am running EIGRP on both the L3 switch and the router
    – user6069
    Jul 16, 2014 at 13:45
  • Both are good suggestions but I can't mark both.
    – user6069
    Jul 18, 2014 at 18:58

You'll need another physical interface on your router that runs at the same speed as your existing physical interface. Once you have that, you can create an etherchannel/port-channel/lag between the switch and the router and you'll need to move your IP address and your sub-interfaces (if you have any) to the new port-channel interface. Here's a guide on how to get it up and running:


  • A layer 3 etherchannel, thanks for the suggestion
    – user6069
    Jul 16, 2014 at 13:46

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