One VLANs spread over two sites

Hi

Is it possible to have one VLAN spread across two geographically seperate sites?

Can we have one IP subnet over two sites.

Thanks

J

Yes, it's possible as long as the two sites are interconnected via switches, not routers. In other words the two sites should be connected like this:

[Site 1 Switch]

---

[Site 2 Switch]

Not like this:

[Site 1 Router]

---

[Site 2 Router]

And not like this:

[Site 1 Switch]

---

[Site 2 Router]

The link between the two switches is typically a trunk.

The thing is that a router is a split point between vlans/subnets. A Vlan cannot exist on one router interface and another router interface at the same time, unless those two interfaces share the same physical link.

Could you explain brefly. Means we have to use layer 3 switch or what. What will be the connecting media. Can we use PIX / ASA to connect sites with VPN and then to switch & still we can have the same VLAN.

Regards

Could you explain brefly. Means we have to use layer 3 switch or what. What will be the connecting media. Can we use PIX / ASA to connect sites with VPN and then to switch & still we can have the same VLAN.

Regards

You can use either a Layer 2 or Layer 3 switch. But Layer 3 switching is essentially routing. You can use a layer 3 switch but you have to configure it properly to do only layer 2 switching between the two sites.

Yes, it's good that you reminded me about VPN. You can have one VLAN extending through the two sites using a Site-to-Site VPN. This way you CAN have 2 routers and/or PIX/ASA in between. Or you can configure VPN on one router/PIX/ASA on one site and then connect the other site using a switch, in this case the VPN client will be the user PC it self.

A VPN is as you know a tunnel done over IP, so it doesn't matter how many routers or switches are in between as long as the two ends of VPN (client/server) are configured properly and the IP traffic is routable.