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uBR 7246 bridging?



I have a question.

How can I solve my problem on the picture?

Is it possible that the default GW is the internet router and the CMTS is acting as a bridge?


paolo bevilacqua
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And why should you bridge ?

As you can see the whole subnet (/24) is on the internet router. It is not possible to subnet it.

It is a production network and I can not change anything.


Did you ever get this figured out?

I'm in exactly the same boat now myself.

Any help you could offer would be greatly appreciated.

Many thanks,



bridging is definately not supported.

Our customer deceided to use DHCP only, and I think this is a better solution than PPPoE.

But you can use the uBR as LAC if you want PPPoE.

Here is an example:

Hi and Thanks for getting back to me.

I'm migrating from Arris C3 CMTSs to the uBR7246 platform.

On a simplified level, our current network config has Business User Cable Modems using one Config file while Residential User use another Config file.

For the Arris C3 CMTS, I just specify which Cable SubInterface to attach CPE traffic TO in the Modem Config File, and I have this Cable SubInterface in the same Bridge-group as a FastEthernet SubInterface which has an associated VLAN Tag.

This results in the Traffic Passing through the CMTS and appearing on the other end as Tagged Traffic.

I need to be able to Separate Business Customer Traffic from Residential Customer Traffic and in addition to this, I do have a few Customers that would use PPPoE in their own Private VLAN.

What you suggest above might work for the PPPoE Customers, but are you saying that that I can't separate the other customer traffic into Business and Residential VLANs?

There are various 'Bridge' commands in the uBR.

If not for Bridging Interfaces for Traffic, what do they do???

Router(config)#bridge ?

  <1-255>            Bridge Group number for Bridging.

  cmf                Constrained multicast flooding

  crb                Concurrent routing and bridging

  irb                Integrated routing and bridging

  mac-address-table  MAC-address table configuration commands

Router(config)#bridge 1 ?

  acquire                   Dynamically learn new, unconfigured stations

  address                   Block or forward a particular Ethernet address

  aging-time                Set forwarding entry aging time

  bitswap-layer3-addresses  Bitswap embedded layer 3 MAC adddresses

  bridge                    Specify a protocol to be bridged in this bridge group

  circuit-group             Circuit-group

  domain                    Establish multiple bridging domains

  forward-time              Set forwarding delay time

  hello-time                Set interval between HELLOs

  lat-service-filtering     Perform LAT service filtering

  max-age                   Maximum allowed message age of received Hello BPDUs

  priority                  Set bridge priority

  protocol                  Specify spanning tree protocol

  route                     Specify a protocol to be routed in this bridge group

  subscriber-policy         Subscriber group bridging

I'm using IOS v12.2(33)SCE.

Many Thanks for your time,



first I have to say that I am not an uBR professional, I only configured two uBRs, one 7246 and one 10012. Both had a more or less straightforward configuration.

The first thing that comes in my mind are two Bundle interfaces, one for Business and one for Residential customers.

I tried to bridge the interfaces facing the CMs and I got an error message, later I read that the 7246 does not support it.

Maybe you can bridge between Ethernet interface, but you don't need that.

Thanks Smailmilak,

Looks like I'm going to have to redesign my network to Route CM CPE traffic if I want to use the uBR Platform.

Seems like a silly limitation to have, but I guess that's just Cisco for you.

Thanks again for your time and help.


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