Having a problem to extend VLAN over WAN link

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Apr 28th, 2010

I need to extend the vlan that has been created in the cuurrent facility core switch, to another building

over a WAN link. The scope is to route the traffic to wards the onsite(from current building).

I have this problem too.
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Kevin Brennan Wed, 04/28/2010 - 02:00

Hi Uday,

Before getting into how this might be done, what is it that you'd like to achieve? - There are a number of drawbacks and innefficiencies to extending a broadcast domain over geographical sites.

What type of WAN circuit do you have - or do you have one yet?

If it is a L3 circuit, you might want to look at L2TPv3 (Layer Two Tunneling Protocal, version 3).

If you have a L2 ethernet circuit you might be able to trunk a few VLANs over the circuit (if the carrier supports dot1q) or else you might only be able to plug in two access ports at each end of the link.

Sorry to repeat myself, but if there is any way to achieve what you want without splitting a VLAN across sites I'd strongly recommend investigating it.



mail2udaykiran Wed, 04/28/2010 - 02:10

Thanks for looking into this brennan,

Here I am explaining you that what might be done.

We have 2 branches connected with PRI link (in the same city).

And we have client site and that has connection with only one of our branch. This connection has some limitations. We natted one private VLAN to a single public IP, and we are doing the routings and all to wards the client. For client the source IP is unique(eventhough there are several hosts)

Now we want to give the connectivity to the client site from the other branch also.

Could you please tell me the best way to do it.

Kevin Brennan Wed, 04/28/2010 - 02:17

Hi Uday,

I don't think extending a VLAN is what you're looking for.

If I understand correctly, is this your setup?


You want to have access to ?

How does connect to ?

Is it a VPN?

I presume you are using static routes between and ?


mail2udaykiran Wed, 04/28/2010 - 02:25

Yes Kevin


---T1---- ---T1----

Now I want the connectin should be  from to thourgh

Coz we cannt go for aother link btw and . And moreover people will be working from to the same client.

And the connection btw and is on (static routes not on VPN)   

Kevin Brennan Wed, 04/28/2010 - 02:32

Hi Uday,

I'm with you now.

You need two additional static routes. This is assuming that there is full ip connectivity between and .

On you need a static route to the network behind with the next hop of

On you need a static route to the network behind with the next hop of

The syntax for this is

ip route x.x.x.x y.y.y.y z.z.z.z

Where x.x.x.x y.y.y.y is the network and mask of the destination network and z.z.z.z is the next hop to that destination.

Depending on the relationship between yourself and your client, you might want to implement some ACL's to restrict the flow of traffic between you.



(EDIT: You mentioned NAT, could you elaborate on that, as it may have a bearing)

Message was edited by: brennan.k

mail2udaykiran Wed, 04/28/2010 - 03:29

As I told eariler.....Client is allowing my traffic as single source


From the private vlan 192.168.24.X is natted to that IP.

in I created 192.168.34.X and I am routing them to and also natted this praivate VLAN to the same IP(196.12.X.X). 

Kevin Brennan Wed, 04/28/2010 - 03:32

Hi Uday,

I'm not sure if that would be possible with your NAT configuration.

Can you post your configs (without any sensitive information)?


shailesh.h Wed, 04/28/2010 - 09:31

Certainly you can achieve the same without extending LAN. Now if site 2 allowed only site 1 to communicate then there are couple of options available to you.

  • You can use dynamic or static routing
  • you can NAT client IP behind site 1

I have put my current understanding of your requirement in the diagram attached. Need basic information to suggest something workable for you

  1. What is installed at site1
  2. How Site1 and site 2 connectivity
  3. How is currently Client and site 1 connectivity
  4. How is Client and site2 connectivity

What is the challenge

Share the config of the network devices in the path




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