Well, I tried it my lab. switchport trunk allowed vlan has no impact on CDP, VTP, LACP, STP etc. They are still sent in vlan 1 even if it is not allowed on trunk.
http://www.cisco.com/en/US/docs/switches/lan/catalyst2940/software/release/12.1_19_ea1/configuration/guide/swvlan.html#wp1150302
Aivars
|
> |
Aivars, Best practice would be to remove VLAN 1 from the list of trunked VLANs. Mike On Mon, Dec 10, 2012 at 10:39 AM, Aivars <[email protected]> wrote: Hi, I thought that CDP essence is to help understand what device you have at the other end of the wire no matter what. You just plug one end of the cable into one box and the other end into another and you get your CDP neighbors. Besides other side usage like in IP phone communication with switches this is why anybody would use CDP. Right? Up until this morning I also thought that CDP frames are always sent untagged. This is the way I would do it. Well, I was wrong. Actually on Catalyst switches CDPs are sent in vlan 1. If you make some other vlan native on a trunk port, CDPs are sent with dot1q tag "1". vlan dot1q tag native will also do the same trick. Now imagine a brand new shiny IOS-XR box, ASR9k for example. If it has no subinterface configuration with encapsulation dot1q 1, CDP will be broken. It will send CDPs with no tag and Catalyst will be happy about it. It will show ASR as CDP neighbor. ASR instead doesn't now what a hell tag "1" means and drop these frames. Cisco thinks - this is expected behavior. What do you guys think? Is this a bug or a feature? Should it remain as it is? Aivars _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/ |
_______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
