[c-nsp] VLAN 1005 Translation?

[Brett Frankenberger]

On Mon, May 26, 2008 at 03:17:32AM -0400, Paul Stewart wrote:
> 
> So, I thought I might be able to do VLAN translation - is that possible on
> 1005?  I just want to take 1005 and translate it to 900:

I think it's possible, but haven't ever tried it.

> interface GigabitEthernet4/7
>  switchport
>  switchport trunk encapsulation dot1q
>  switchport trunk allowed vlan 18,84,108,127,131,139,151,163,164,172,175,176
>  switchport trunk allowed vlan add
> 180,193,195,196,198,200,243,245,326,341,364
>  switchport trunk allowed vlan add 381,382,389,391,402,696,1005
>  switchport mode trunk
>  switchport vlan mapping enable
>  switchport vlan mapping 1005 900
> 
> Is there anything I can do to make this work or is my config wrong?  Also,
> do I have to translate *back* somewhere such as the "outgoing" port?

VLAN translation logically occurs as the last step before transmission
and the first step after reception.  So, with the "vlan mapping"
configuration above, the VLAN will be 900 everywhere in the switch
configuration (other interfaces, SVIs, the vlan database, etc.) but
will appear on the physical 4/7 port with a tag of 1005.  (That is,
right before transmission, the 900 will be replaced with 1005.  And
reight after reception, the 1005 will be replaced with 900.)

So ... in your configuration above, what happens is a frame is received
with a tag of 1005, that's replaced with 900, and then the frame is
discarded since vlan 900 is not allowed on the trunk. 

As a minimum, the following is needed:
   interface GigabiEthernet4/7
    switchport trunk allowed vlan remove 1005
    switchport trunk allowed vlan add 900

You also need to make sure vlan 900 is configured on the switch (in the
vlan database, etc.) and that you refer to it as vlan 900 anywhere else
it's referenced (in SVIs, on other interfaces, etc.).

     -- Brett