bridging across WAN links

[richmorrow624]

Is the idea behind bridging across WAN links to allow a remote site to be on the same layer 2 link and subnet as the Main site?

For example in a DR scenario, you could configure the DR site to be on the same subnet as the Main site as far as the remote branches are concerned?

[paolo bevilacqua]

What is DR?

yes, with bridging everything will be in the same L3 subnet. That is usually a bad idea especially for WAN links because:

- wasted bandwidth due to broadcast/multicast flooding

- overhead due to L2 addresses in WAN packets

- cannot to compress traffic

- cannot crypt traffic

- poor control of traffic flow due to inability of L3 separation

- harder to diagnose and troubleshoot.

- much harder to design for a backup.

- no performance advantage over routing, actually the opposite.

If you are new to networking, don't think that bridging is a shortcut to success, it is not.

[richmorrow624]

Thanks for the reply,

DR is the Disaster Recovery site.

This was set up by someone else, they have a bridge connection from the Main Site to the Disaster Recovery site.

All the Server subnets are in the same VLAN(I think why they did it this way).

[paolo bevilacqua]

There is no reason for a disaster recovery site to use bridging instead of routing. The real problem is: "If I bring down the main site, how and by which addresses the branch sites and other offices will connect ?".

Bridging in itself does't offer a solution to this problem.

Unfortunately, there is no easy answer. each application, vendor, integrator can propose a different solution and I have yet to see one that is totally satisfying. Then it depends by the customer. Some are happy just having an almost ready copy of all-data, other pretend small switching times.

Designing something that works for real (not on paper only) can be difficult, expensive and time-consuming.