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Catalyst 3650 CDP behavior when received CDP Frames are tagged wrong

julian.bendix
Level 3
Level 3

Hi all!
I would have a question about an issue with CDP I am facing.
We have an AP which is hitting the Bug CSCef35717.
So the AP is sending CDP Frames tagged with VLAN1 even though we have a trunk with native VLAN different than 1.

We have the issue that the Switch is now not seeing the AP as CDP neighbor anymore.
But the AP is seeing the Switch as CDP neighbor perfectly fine.

I created a SPAN Session for the Port where the AP is connected to.
And I do not see any inbound CDP packets at all.

I have some problems understanding why it would bother the Catalyst 3650 that the CDP Packets are tagged in VLAN 1.
Why is the Switch not accepting the CDP Packets and .. if we are really hitting the mentioned Bug .. obviously dropping them as well?

Would be really nice if someone could shed some light on this case for me.

Thanks a lot in advance and best regards!

3 Replies 3

Hello

FYI - Control  plane protocols such as CDP are always sent over vlan 1 even if you have specified a different native vlan, As such  that bug seems to suggest the AP attached to the switch on the trunk sends its cdp messages in vlan 1 as tagged frames but naturally the switch trunk is expecting vlan 1 control traffic to be untagged so it denies them.

The reverse is different (switch-> ap) the switch sends cdp frames over the trunk towards the AP as untagged and the AP expects them and allows them.


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Kind Regards
Paul

Hi Paul,

 

thanks a lot for the reply!
We have a Trunk between Switch and AP with native VLAN 7,
so Frames being tagged in with VLAN 1 would be totally fine.

I also see absolutely no indication about this when I turn on CDP Debugging (packets, events, ..) on the Switch.
Would that be something to expect when hitting the mentioned bug on the AP?

Thanks a lot and best regards!

Hello,

 

just out of curiosity, does the bug apply to LLDP as well (lldp run/show lldp neighbors) ?

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