Allow the host to specify VLAN membership

[STUART KENDRICK]

Normally I configure data center switch ports to statically assign VLAN membership

interface GigabitEthernet2/1

switchport

switchport mode access

switchport access vlan 42

Now, I want to reverse that -- I want to define VLANs on the switch and let the host pick which one it wants to belong to.

vlan 12, 22, 32, 42

interface GigabitEthernet2/1

switchport

switchport mode ?

I'm getting stuck here.  'switchport mode dynamic'?  No, that enables DTP, which is Cisco-proprietary, not supported on standard Intel/Broadcom/whatever drivers in the average Linux/Windows host.  'switchport mode trunk' and 'switch trunk allowed vlan 12,22,32,42'.  No -- that didn't work -- the end-station brings up link but cannot go any further; and the switch shows the port as belonging to vlan 1.

Pointers?

--sk

Stuart Kendrick

FHCRC

[Chad Peterson]

Hi Stuart,

The only way I see doing this is configuring a trunk, allowing only the desired possible vlans, and then on the host specify which vlan you want to use by having it tag its traffic with that VLAN number.  You'll have to make sure your end host knows how to do 802.1q trunking.

Chad

[Chad Peterson]

The only way I could see doing this w/o using 802.1x or VMPS (which both don't allow the host to choose vlan) would be to provide a trunk allowing the possible vlans that will work...then on the host tag the traffic in the vlan they wish to join.

So if you wanted vlan 12, 22, 32, 42 to be possible, on the switch:

Switchport trunk encap dot1q

Switchport mode trunk

Switchport trunk allowed vlan 12, 22, 32, 42

On the host you will have to specify which vlan it will use.

[STUART KENDRICK]

Thanx Chad.

--sk