How to find server vlan information on the switch

Unanswered Question
Feb 8th, 2007

Hi guys,

I have a setup like my all the switch ports are configured as trunk ports (dot1q)

i have vlans configured on the sever(win2003) (interface)and those are belongs to different vlans.

in that case how i can identify which sever belongs to which vlan from the switch.

"without knowing the server vlan information "

Please post your suggestions



I have this problem too.
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Overall Rating: 2.5 (2 ratings)
etamminga Thu, 02/08/2007 - 10:48

Hi Krishna,

I do not fully understand what's being asked, but ....

You can find out what device is on what vlan by investigating the output of the "show mac-address-table [vlan x]" command.

The output can be combined with the output of "show arp" (cisco) or "arp -a" (windows) to match the mac- and ip-addresses. Ping the server IP-adresses before you issue the arp statements.


Erik Tamminga

m-haddad Thu, 02/08/2007 - 11:00

Hello Krishna,

If you know the mac address of that server you can go to the switch and issue the command:

show mac-address-table | inc "last few digits of the mac"

You will get on which VLAN this server was captured.

Let me know if this answers your question,

Remark: This is a workarround approach, however, you should know which server is connected to which VLAN because I understood in your scenario the taging of VLANs is done on the Win2003 server.


Appreciate your rating,

gopikrish Thu, 02/08/2007 - 11:19

Hi Haddad,

Thanks for your reply

thats what i am looking.

is it possible to test(find) the sever interface whether it support for dot1q tagging or not?



m-haddad Thu, 02/08/2007 - 11:25

Hello Krishna,

Go to the interface which is connected to the server and issue the command

switchport mode desirable

switchport trunk encapsulation dot1q

The above will let the switchport to try negotiating trunk via DTP.

Then go to the global configuratio mode and issue the command

show interface trunk

It will show you which interfaces did negotiate as trunk. If the interface negotiated a trunk then the server does support trunking using dot1q tagging. If not then your server interface card does not support it.

Another ways it go to the network card manufacturer webpage and check if the interface model that you have does support trunking or not. Usually, Intel based servers are not shipped with supported interfaces unless specified by customers. VMWARE servers support trunking on their NICs.

Let me know if this answers your question,


gopikrish Thu, 02/08/2007 - 11:52

Hi Haddad,

Thanks so much

is it possible do the testing in cisco cat OS ?



m-haddad Thu, 02/08/2007 - 11:58


Yes you can do this on Cat OS. Most of the commands are the same however you have to use the "set" before the command. If you want, you can look the CAT OS commands on cisco documentation. The link is:

Then you go the switches types and you choose the model you have and you get all the documentation.

Let me know if you need anything else, ;-)


gopikrish Thu, 02/08/2007 - 12:19

Hi Haddad,

I found the commands

i think it should be like this

set trunk 1/2 desirable

set trunk 1/2 on dot1q

sh port 1/2

I think this the way

is there any other options available to check this ?

Thanks for your help


m-haddad Thu, 02/08/2007 - 12:24


To check which ports are in trunking mode you have to use "show port trunk"

Hope this helps,


gopikrish Thu, 02/08/2007 - 12:30

Hi ,

I think it show all the information about the trunk ports which is configured on the switch

however i need to find only about the particular port. whether it is negotiated or not (with dot1q)

I just translated the commands which you have posted on IOS.

Please suggest..



m-haddad Thu, 02/08/2007 - 12:42

It will be

show port trunk 1/2

This will give you the status of this interface only,


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