sub-interface encapsulation

Unanswered Question
Jan 1st, 2009


I have some 2600 routers that do not allow for encapsulation to be set when a sub-interface is created. I guess this is due to IOS but was wondering how you configure a sub-interface without the encap command available. I imagine it is a possibility since it allows for the creation of the sub-if but can't figure out how. Is it done by using the bridge group commands?



  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Giuseppe Larosa Thu, 01/01/2009 - 14:54

Hello Richard,

if the encapsulation command is not supported I think you cannot use Vlan subinterfaces.

In this kind Of IOS images bridge-group commands are supported on physical interfaces.

Once it happened to me to load an IOS image in a Cisco 7200 or 7500 with the same behaviour I tried to use them with no success.

The Cisco engineer that was following us told us to change it.

missing to define a way to multiplex demultiplex frames over the trunk should cause forwarding problems.

However, you can try with the bridge-group command if supported and using BVIs (IRB) but I usually saw bridge-group supported on main interfaces only

Hope to help


richard.m.gilbert Thu, 01/01/2009 - 15:05

Thanks Guiseppe,

How should the distant end sub-interface that supports dot1q be set up if using the bridge-group command on the physical interface at the local device?


Giuseppe Larosa Thu, 01/01/2009 - 23:21

Hello Richard,

sorry if I've been unclear:

if enc command is missing AND bridge-group can be given only on main interface


you cannot use VLan subifs

Look for an IOS upgrade.

Hope to help


jaregalado Thu, 01/01/2009 - 23:37


This is a common issue with low end IOS versions on 26xx routers, typical solution is to upgrade IOS and maybe memory on router, depending on the chosen IOS. Take a look at this previous post:

More posts on this issue can be found searching for "encapsulation dot1q unrecognized".



This Discussion