Solved: Why so many neighbors?

sterdnotshaken · ‎01-27-2012

Howdy,

Hey, just wanted to check and see if anyone might have the answer to this potentually simple question...

Stage setting: Big network, lots of L2.

Why am I seeing, when I issue "sho cdp neighbor" 30+ neighboring switches? CDP's behavior should be limited to a pair of devices... Would VPLS cause this?

Thanks!

Leo Laohoo · ‎01-27-2012

Yes. This could also be another cause.

I had experienced this in my previous work. Our core and access switches were Cisco but our distro was Enterasys. Whenever you do "sh cdp n" on the core switches, you don't see the distro. You see the access switches. Made you think the access switches were connected directly to the core. The only give-away was the interface as all the access switches were connected to the same interface on the core switch.

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Reza Sharifi · ‎01-27-2012

Hi,

CDP shows directly connected devices. So, If you have 30 switches uplink to one core switch. The core switch shows 30 neighbors.(they can be L2 or L3 neighbors). do a "sh cd nei det" that will show you more info retarding the neighboring devices.

HTH

Leo Laohoo · ‎01-27-2012

Gets worst no just by switches. VoIP wired sets, routers, WAPs, etc will show up in "sh cdp neighbors" output.

sterdnotshaken · ‎01-27-2012

Forgot to clarify... I see 30+ neighbors on a switch that has 1 port channel (2 interfaces) to the distro layer switches... I see this same list on all of the access layer switches. Could this be caused by having a mixed vendor environment where the Distro\Core layer is passing CDP packets on per not recognizing CDP and, per large broadcast domains (and VLANs that traverse the distro\core), switches on the other side of building\campus receive these cdp packets and respond? Thus building a "All Access Layer" CDP neighborship table?

Leo Laohoo · ‎01-27-2012

Yes. This could also be another cause.

I had experienced this in my previous work. Our core and access switches were Cisco but our distro was Enterasys. Whenever you do "sh cdp n" on the core switches, you don't see the distro. You see the access switches. Made you think the access switches were connected directly to the core. The only give-away was the interface as all the access switches were connected to the same interface on the core switch.

sterdnotshaken · ‎01-27-2012

Good to know. Thanks guy's for taking time out of your day to help out a fellow peerhead!

Leo Laohoo · ‎01-27-2012

Thanks for the ratings.

We were all noobs once.

jimmysands73_2 · ‎01-28-2012

Maybe free beer and women? Thats always drawn me many neighbors