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Troubleshooting Question

host flapping between ports

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Last Modified: 2020-10-13
I have this error message on one of my swiches, sw32.  Not sure what  or how a host can flap between two different ports.  Any idea's how to resolve?
I've read online it could be a loop, that I should trace both ports and what is plugged into each one? I will do this on Monday.  


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Mohammed BasheerInfrastructure Administrator
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Commented:
Hi
  • The Vlan 1 is available in the switch? If not, should create.
  • Check the SFP, fiber port and patch cable. Try a clean spare patch cord
  • If port-channel is configured, make sure both ends are configured. If one end is configured and other end not, spanning-tree loop may occur.
  • Also, check a device is not connected twice to the switch.

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Hello ThereSystem Administrator
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nociSoftware Engineer
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some oneNetwork Architect
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Commented:
You may also get this if a device is connected wirelessly. If you have wireless access points on the two ports in the error log, it's probably a client roaming between APs too often.
DanNetwork Engineer

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Commented:
A few things to check, I will check it today or tomorrow.  I'll get reply soon with what I find.
DanNetwork Engineer

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Commented:
The switch in question is my switch where all my APs are plugged into.   So only APs are plugged into this switch, no end user computers, phones, or other devices.   Only APs are connected to it.  So the only thing I can think of is, are users on their phones, or laptops, as they move between APs, the APs are sending the MAC info back to the firewall, as my firewall is my wireless controller, and the switch is seeing the MAC on from 2 different ports.
I think that's what's happening, but how would I fix that on the switch, is there some configuration I can configure that will not cause it to flap?
Benjamin Van DitmarsSr Network Engineer
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Commented:
this will happen in misconfigured accesspoint or someone is creating a loop with a small unmanaged switch.
there are hard to find.
you can always configure the max amount os mac's that can the connected to an interface. we use the amount of 4
when dealing with phones and passthrough to a computer. this is a safe value

DanNetwork Engineer

Author

Commented:
Regarding the access points, I am using Sophos APs, so there's not a lot to configure, the firewall is the controller and all the basic settings have been configured correctly, the channels are set to auto, and a few other options are set to auto as well.   So since I know that ONLY APs are plugged into the switch, there's no 5 port switch or anything installed, so I'm a bit puzzled why this would be happening.  

On the switch, are you saying I should configure only the AP MAC?


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DanNetwork Engineer

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Commented:
Got it, so if there's only a few flaps, no big deal, but if there's a lot, there's an issue with my design.

Thanks for the info.

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