ATM subinterfaces on same network

Unanswered Question
Jun 4th, 2009

I have several ATM subinterfaces I need to make part of the same network.

I have used ip unnumbered and bridge-groups in the past.

Looking for recomendations for which way is better or a new idea as well.

The only issue I have had with using ipnummnered is setting static host IPs. I see there is a polling option for unnumbered interfaces, not sure if it is better to avoid use of that or not.

Your input is much appreciated.



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Giuseppe Larosa Thu, 06/04/2009 - 11:07

Hello Dan,

I think bridge-groups with IRB are the better solution for this scenario.

Hope to help


Daniel Graham Fri, 06/05/2009 - 10:29

I am at a loss here.

I am upgrading from a 7500 to a 6500 and it is becoming very frustrating as many of the features are not availible.

I need to connect 100 ATM sub interfaces to the same network. They do not have to be bridged. I simply need them all part of the same network and have the ability to set static ip's on the host side of the atm curcuits.

I have tried using IP Unnumbered and this works fine with DHCP but not when setting a static IP on the host side. The 6500 does not support ip unnumbered connected host polling.(that i can see)

I have tried using bre-connect on the atm PVC's. This however can only bridge a PVC to one "unused" vlan ( PVC 1/1 maps to vlan 10, PVC 1/2 maps to VLAN 2 etc.) they cant be mapped to the same vlan.

I have tried using bridge domain on the ATM PVC's. This would appear to work ok except there appears to be a limit on how many PVC's or (ports) can belong to a single bridge domain, and its not enough to support all of my ATM PVC's that need connectivity to the same network.

Currently I am using a bridge-group on my 7500 router. I have a BVI interface and under the ATM subinterface bridge-group # is specified.

On the 6500 BVI interfaces dont appear supported and the bridge-group command under atm subinterface config is not there.

I also read that bridge protocol ieee is not supported under the 6500 platform.

Is there anything other command / feature etc. I can use to make this work?


Paolo Bevilacqua Fri, 06/05/2009 - 10:38

Seems like it was a poor design since the beginning and the 6500 is enforcing sane routing more than the 7500.

You can use host routes to send traffic to whatever subinterface/pvc you want.

Daniel Graham Fri, 06/05/2009 - 10:43

I couldnt agree more. Unfortunently im stuck with making this work/implementing something new.

This is how it is setup on a small scale:

BVI with address of

ATM 1.1 bridge group 1 > host IP

ATM 1.2 bridge group 1 > host IP

Both hosts gateway are set to BVI interface IP of

Whats the best way to move away from this?


Paolo Bevilacqua Fri, 06/05/2009 - 10:45

Put back the 7500, advise customer of the seriousness of the issue, schedule a day zero global reconfiguration (spokes and remote).

Daniel Graham Fri, 06/05/2009 - 10:54

Can you give me an example of what you meen by spokes and remote. Just want to make sure im on the same page by what you meen.


Paolo Bevilacqua Fri, 06/05/2009 - 11:09

What Giuseppe is also saying. Check what is in the remote sites, ideally a router but it not even said.

Giuseppe Larosa Fri, 06/05/2009 - 10:57

Hello Dan,

after having read the other posts I agree with Paolo.

I've only one doubt a setup like the one you have described makes me think that at remote sites there are no real routers but devices able to perform bridging between a lan interface and an ATM pvc.

I once tried some boxes that were doing this between a lan interface and a serial interface.

if so the change is even bigger and would require the deployment of routers on the remote sites.

in the mid time keeping the old C7500 is a safe bet.

Hope to help



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