Strip VLAN tags on a trunk connection

[rasmus.elmholt]

Hi

Does anyone know how I strip VLAN tags from a trunk connection using a Cisco Switch?

From our ISP we get our different sites delivered on individual VLANs on a trunk. But I want all sites on the same L2 network/subnet.

Any idea on how to achieve this the easiest way?

[Seb Rupik]

Hi there,

Trunk these ISP tagged VLANs through your network until it gets to a device which supports VLAN translation/ mapping.

Keep in mind that the VLAN translation is not just applied to a single switchport but to groups of ports on a linecard (I'm thinking of a 6509 from personal experience), so you may need to spread your incoming connections across the chassis to ensure that there is no translation overlap.

cheers,

Seb.

[Richard Burts]

It is unusual to receive traffic from remote sites on separate vlans and want to put it all into the same layer 2 vlan at your main site. Remember that it will result in any broadcast traffic from any site being sent to every machine at every site. But if that is what you want to do this should work. In my suggestion you will need two switches. Let us assume that you are receiving traffic on the trunk on vlans 10, 20, 30, and 40. And let us assume that on your site you will use vlan 50. On switch 1 configure a trunk to carry vlans 10, 20, 30, and 40. Then configure an access port in each of those vlans. Connect the access ports for these vlans on switch 1 to access ports on switch 2 which are all assigned to vlan 50. No trunk on switch 2. Now vlan tags will be gone and all traffic will be in the same vlan and same subnet.

HTH

Rick

[rasmus.elmholt]

Hi Richards
Thank you for the reply, the only problem is that the solution needs to scale well, and be auto provisioned. I have between 50 and 2000 sites, and they change all the time.

[Richard Burts]

Thanks for the additional information. Especially if you have between 50 and 2000 sites I would question putting them all into a single layer 2 network. But if this is what you want to do then it may be best to look into what the ASR can do for you.

HTH

Rick

[rasmus.elmholt]

Hi

Do you know the smallest switch with support for VLAN mapping?
I have a 3400 ME maybee I will try to put some test configuration on it, to se what it can do.

Thanks for the input.

[Seb Rupik]

Hi there, 

Since you have ASR920's available they do support VLAN translation. The command you are looking for is:

!
int <int>
  rewrite ingress tag translate 1-to-1 dot1q vlan-id symmetric
!

I can't find any information regarding maximum translations or port-group limitations..

https://www.cisco.com/c/en/us/td/docs/routers/asr920/configuration/guide/ce/16-8-1/b-ce-xe-16-8-1-asr920/vlan-translation-with-qos.html#task_112AAAF5629B4601B9F50A2DFFF9B556

cheers,

Seb.

[dbeattie]

This can be done on an ASR900 series router. I tend to opt for the ASR920-12sz-im. You can add/remove tags in the service instance. It tends to be seen as a SP function, so is not often available in traditional enterprise kit.

Hope this helps.

Dave

[rasmus.elmholt]

Hi Dave

The setup is already terminated at our ASR920.
I will have a look at it. Is it also called VLAN mapping on this line of routers?