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Cisco announces new innovations in SD-WAN, ISRs, SD-WAN Services, and Catalyst 9000 Series switches


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Beginner

Flapping ports

Hello,

 

Flapping ports in my experience is normally to do with a loop or dodgy cable.

 

Can someone back sense of this flap and why so many ports/mac addresses?

 

This is from a 3750 the root switch which has a trunk to a 2960 on 2/0/11 and I see this from time:

flap.png

And on the other end of the the trunk on the 2960 I see this:

flap2.PNG

Gig 0/24 is the trunk port back down to the 3750.  Does it look like what ever is on Gig 0/2 is causing the issue?

If so why does the 3750 then flap on most of it's ports after?

4 REPLIES
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Collaborator

Re: Flapping ports

check what is the device connected to that port by using show cdp neigh

 

Check the network switches for misconfigurations that might cause a data-forwarding loop. 

 

check spanning-tree configuration.

 

 

BB
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Beginner

Re: Flapping ports

Sh cdp and spanning tree look as they should.

 

could a look on a device beyond the 2960 cause this flap and if so why would ports on the 3750 flap too?

 

Setup

3750------->2960------->3 ports going  to 3rd party LAN

Collaborator

Re: Flapping ports

Post the configuration to have a look for what is wrong in the configuration.

 

is this working and having issue recently or have you had any changes recently which causing the issue

BB
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Hall of Fame Guru

Re: Flapping ports

MAC flapping is a sign that Etherchannel is not configured properly.
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