So I have a cisco 2811 router and 2 3560 switches

Currently the router is connected to Core1 only, what i would like to do is use the other port on the router (fa0/1) to connect to Core 2.

How do I go about doing this? The router currently has the ip and Core 1: Core 2:

I tried to make another interface on the router but it complained that the ip address that I set conflicted with the one of fa0/0 to Core 1

2 Answers 2


You need to enable IRB (integrated routing and bridging) on the two router ports. You create, in essence, a L2 bridge between them. You then put the IP address in the BVI (bridge virtual interface).

Be sure to enable spanning tree, as you are creating a second L2 path.

  • Please could you give me an insight as to the commands I would need to enter?
    – NickCarlt
    Feb 2, 2018 at 18:46
  • This document should be able to help you out with getting IRB configured.
    – A-A-Ron
    Feb 2, 2018 at 18:46

As router is layer3 devices .Hence each interface connected and configured with each networks .

In this scenario both core1 & core 2 switch are connected with two router interface with same networks ip address 192.168.1.X . That's the reason getting ip address conflict error while other router port configured .

To avoid this error configure another networks address to another router interfàce .

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