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Layer 2 over Layer3 connection

Has anybody done a 'spanned' lan over a layer 3 connection (PRI terminating on two routers) so that devices on both ends are on the same LAN? I think Cisco calls it IRB, and they have examples on one router, but my need would be to have it on two routers.

I know it is bad design and it isn't my choice, just may need to make it work.

Hall of Fame Super Blue

Re: Layer 2 over Layer3 connection


Have a look at L2TPv3 which is a good approach to extending a L2 vlan across L3 links. I have used this before and it worked fine -


Community Member

Re: Layer 2 over Layer3 connection

You can use IRB and GRE tunnels. I had to do this for a company that we acquired that was using their routers to bridge traffic over frame-relay. To give them a migration path I configured layer 3 subnets across the frame-links and used GRE tunnels and bridge groups to bridge the ethernet to the GRE tunnels. It was a very ugly configuration and I wouldn't recommend it as a long term solution. If your networks have a large number of Windows computers, the NetBIOS activity severely affects the performance of your WAN link.

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