How do I configure CDP to use the native VLAN ?

ajsouthard · ‎05-01-2003

I am using dot1q trunking between my switches with vlan 1 not allowed and vlan 200 set as the native. CDP continues to send in vlan 1 and hence does not work. Even when I set "vlan dot1q tag native" it still uses vlan 1.

milan.kulik · ‎05-02-2003

Hi,

after setting native VLAN to 200 and disabling VLAN1 on 802.1q trunk CDP should be still sent on VLAN1 (tagged) in spite of VLAN1 beeing disabled.

VLAN1 is disabled just for user data.

So CDP should be working OK - sent and received on VLAN1 - I tested it in my lab two weeks ago.

The only problem I know may be with Cat3550 - there is a bug causing CDP not to be sent at all while VLAN1 disabled on trunk.

Regards,

Milan

ajsouthard · ‎05-02-2003

Thanks for that.

Actually I am using 3550s so that may explain it.

I have a sniffer in line and do see CDP packets being sent tagged in vlan 1 but when I do a debug on the 3550s they are not shown as received and CDP does not work. If I allow vlan 1 on the trunk then CDP does work.

Also I wonder why CDP is sent tagged and other "control/management" type traffic like PVST is sent untagged. When I configure "vlan dot1q tag native" then most "control/management" including PVST is tagged as native but CDP remains tagged as vlan 1. Maybe this is bug.

robhorniachek · ‎05-02-2003

Are you running VTP? I bet you'll see the same thing... There is a socument called something like 'Best practices configuration for 4000/5000/6000 switches' - in there, Cisco recommends trunking VLAN1 for CDP and VTP (and others), which will only work in VLAN1.

Hope that helps...??? If needed, I think I can find a link to that doc.

ajsouthard · ‎05-02-2003

Thanks that helps a lot.