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Cisco Employee

Extending VLANs across routers connected via serial link

Hello All,

I was able to extend a single vlan across the routers by following the guidelines

from the below link.

In my setup, I bridged ethernet and serial interfaces of the routers.

With additional BVI's and subinterfaces on ethernet, intervlan communication was achieved on each local end of the router's network.But was stuck at extending multiple vlans across the routers i.e I was not able to achieve intervlan communication across the serial link (only one vlan was extended).


--With this setup,am will I be able to extend multiple vlans ?

--What are all the other possible ways to achieve this requirement ?

Thanks in advance for all your suggestions on this issue.



Hall of Fame Super Bronze

Re: Extending VLANs across routers connected via serial link

Extending Vlans over a WAN connection is not a recommended design and does not follow best practice.

However, since you are half way there, I can suggest create GRE tunnels for each Vlan instance....

Cisco Employee

Re: Extending VLANs across routers connected via serial link

Thanks for the response ..

Can you please provide me a document supporting the same?(on both best practices and GRE tunnel information related to this configuration )

Re: Extending VLANs across routers connected via serial link

I have a feeling that finding a document that says bridging multiple vlans across a serial link is a bad thing will be difficult - it is something most people know (probably because they have already been bitten). Design guides and best practice are more likely to refer to keeping VLANs small and local, references to pruning VLANS within a campus etc.

Having said it is a bad idea, it can be made to work. Please note that I am saying this as an academic excercise, I am strongly recommending you do NOT do this.

The serial link needs to be under your control, or something like X25, frame relay, ATM where you can have multiple circuits. If it is a leased line that is fine, use frame relay and make your own circuits.

You will need one circuit per VLAN, and one bridge group. Each circuit is set as a separate subinterface and you bridge VLAN->subinterface.

If you want this to carry IP, you will need to turn IP routing off.

By the way, did I say don't do it? Look at the real requirements and meet them, not what someone thinks is needed.


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