CDP problem

Unanswered Question
Jun 27th, 2009


Two 4500 switches both in HSRP mode, strangely can't see each other in cdp table.But they can see other edge switches as cdp neighbor. Both are connected to each other via fiber uplinks.

Please advice on what could be the issue.


I have this problem too.
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mahmoodmkl Sat, 06/27/2009 - 04:44


make sure u have cdp enabled on the mentioned interfaces.



Giuseppe Larosa Sat, 06/27/2009 - 04:46

Hello Sunny,

there is a direct link between them?

>> Both are connected to each other via fiber uplinks.

check if any side has CDP disabled at the interface level.

Check also the errors on the link both sides this can be a sign of a not working well link.

if they see each other as IGP neighbors on that link the problem can be CDP disabled on one side.

Hope to help


suthomas1 Sat, 06/27/2009 - 07:32

Hi Giuseppe,

Yes both have links connected to each others Gig ports. Cdp is enabled on ports at either sides. No errors seen.

one thing i observed is Switch1 interface connecting to Switch2 shows as down/down(inactive) state & Switch2 interface connecting to Sw1 shows in down( disconnect)state.


Reza Sharifi Sat, 06/27/2009 - 07:53

It sounds like a layer-1 problem

you should change the patch cord that connects the 2 devices together. Are you using the right patch cord with the right interface optic?

SX interface with MM fiber

LX interface with SM fiber



suthomas1 Sat, 06/27/2009 - 08:01

I did try with replacing the chords, but it still remains the same.

Giuseppe Larosa Sat, 06/27/2009 - 08:08

Hello Sunny,

the link is not working at all.

Verify if the type of GBIC / SFP match.

However, it is not uncommon to see failures of these modules.

We had a group of GBICs defective and also SFPs are usually more likely to fail in comparison to GBICs (they are much smaller in volume)

Change one side GBIC/SFP and try again

Hope to help


Reza Sharifi Sat, 06/27/2009 - 08:14

Have you replaced the optics?

Are the optics compatible with your devices?

Cisco boxes don't always work with every vender's optics

suthomas1 Sun, 06/28/2009 - 06:16

fine, i will check for the sfp module also.

Another strange thing is i can telnet & ping to the second switch from within the first switch eventhough interface is down or inactive.Any possible reasons for this.


mahmoodmkl Sun, 06/28/2009 - 22:42


The connection is going through the other links i.e the edge switches links.




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