Transparent Bridging over tunnel interface

Unanswered Question
Nov 7th, 2007

I noticed that the bridge-group command is unavailable for tunnel interfaces on a cisco 3640 router. Is there any way to build a bridge over a cisco tunnel interface? It has to be lan bridge because its going to be a backup connection for a DR site and needs to look like another extension of the lan. The tunnel is ipsec vpn and is going across a cable internet connection. If not, maybe someone could point me in the right direction as to what other options I could pursue.


I have this problem too.
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Richard Burts Wed, 11/07/2007 - 11:26


I can not tell from your post whether the tunnel that you are talking about is an IPSec tunnel or a GRE tunnel. For IPSec tunnel I can understand the lack of support since IPSec is for unicast IP traffic.

I know that it used to be true that bridging over GRE tunnels was not officially supported but that the command was available in the interface and you could configure it. I am not sure if this has changed.

Perhaps you can clarify which kind of tunnel?



luthierone Wed, 11/07/2007 - 11:33

IPSec, but we aren't opposed to using another technology as long as the info is encrypted. As far as I understand, GRE isn't encrypted.

Richard Burts Wed, 11/07/2007 - 14:07


You are correct that GRE is not encrypted. It is possible to combine GRE with IPSec and therefore to get the best of both. If you configure a GRE tunnel between the peers you can then configure IPSec to encrypt the traffic passing through the GRE tunnel.

Be aware that configuring bridge-group under a GRE tunnel is officially not supported. There may be a warning message about this when you configure it. The warning message does not say that it will not work. But it does say that if you encounter problems while running this that the TAC may not be able to help you solve the problem.



luthierone Thu, 11/08/2007 - 07:31

I found somewhere that it may be possible to do it with l2tp...but couldn't find any config examples. So basically, doing a bridge group across the internet isn't supported in any way by cisco?


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