Question about connecting two switches at two different DCs using Layer 2 LAN Extension

[cos@invera]

Hello,

Hope someone can help,

I have two switches at two different datacenters. I was told by the ISP that they have a connection through their network called a layer 2 lan extension. The ends of this lan extension are connected to switch A at dc1 in port gi2/0/12 and the other end is connected to switch B at dc3 in port gi1/0/4.

I am trying to figure out the best way to pass the traffic for all VLANs between the two switches, Switch A has vlans 2, 35, 100, 200 etc and Switch B has vlan 300.

Any help is appreciated.

Jason

[Reza Sharifi]

Hi,

The service providers usually hand off a layer-2 connection on each side, but that does not mean you have to run layer-2 between your 2 switches especially since you don't have the same exact vlans on both sides.  So, in this case, you can change ports g2/0/12 and g1/0/4 to routed ports with a /30 IP and run layer-3. If you want to extend the vlans between sites than they need to be the same. For example, I don't see vlan 300 on side A.

HTH 

[cos@invera]

Sounds interesting, How would i go about doing that? do you know of any documents that can help me out with that setup?

Jason

[Reza Sharifi]

It depends on your platform and design but the layer-3 setup is pretty simple. Example:

Config t

interface g1/0/4

no switchport

ip address 192.168.1.2 255.255.255.252 (this can be any IP. this is just example)

no sh

on the other switch

interface g2/0/12

no switchport

ip address 192.168.1.1 255.255.255.252

no sh

Check to make sure the interfaces are in up and up mode 

sh ip int bri g2/0/12 

the same for the other switch

check your config to see the IPs

sh run int g2/0/12

the same for the other switch

If all good, can you ping from one switch to another?

If ping good depending on the number of subnets you need some static routes.

https://www.cisco.com/c/en/us/support/docs/dial-access/floating-static-route/118263-technote-nexthop-00.html

HTH

[cos@invera]

did all those steps as described but still not working. Maybe i need to follow up with the service provider to figure out why the traffic isn't passing.

Any other ideas to check before?

[Reza Sharifi]

Yes, I would check with the service provider to make sure they configured everything on their side.

HTH

[Joseph W. Doherty]

In answer to your original question, sharing each switch's VLANs with another switch, you would do what you would normally do within a LAN, which should be to configure each switch's port as a trunk.

As to doing what Reza suggests, that depends on whether your switches support L3 and how your routing is configured. Further, with a routed link, you could pass traffic from each switch's VLANs to the other side, but not the VLANs themselves.

Understand what Reza is suggesting is often considered a "better" approach, but there's not enough information to say whether it's actually better for you, or even possible for you.