host flapping in vlan

Answered Question
Nov 16th, 2007
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Hi,

i would like to know what could be root cause(s) that can make a single vlan got host flapping? in my case the router connection became very very slow even cannot be telneted due to high CPU utilization. a host with MAC address has made this router and access switch on the same vlan having connection issue. when the downlink from router disabled, it came back to normal.fiber has been verified okay. was this due to switch port? gbic?or spanning tree? need your advice here. thanks in advance.

Correct Answer by xcz504d1114 about 9 years 8 months ago

Sounds like a broadcast storm was created. Host flap or mac-flap just means that the exact same mac-address was being written to 2 different ports at the same time. A user probably has a hub attached to your network and thought he could "double" his bandwidth by attaching two cat 5 cables to his hub. Or someone plugged a crossover cable between 2 ports on the same switch, both ports would have to have BPDU filter enabled on them for that to be an issue though.

Correct Answer by dominic.caron about 9 years 8 months ago

Looks like a L2 loop.


You need to find which 2 port are looped and remove the cause of the loop from your network.

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Correct Answer
dominic.caron Fri, 11/16/2007 - 08:04
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Looks like a L2 loop.


You need to find which 2 port are looped and remove the cause of the loop from your network.

Correct Answer
xcz504d1114 Fri, 11/16/2007 - 08:40
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Sounds like a broadcast storm was created. Host flap or mac-flap just means that the exact same mac-address was being written to 2 different ports at the same time. A user probably has a hub attached to your network and thought he could "double" his bandwidth by attaching two cat 5 cables to his hub. Or someone plugged a crossover cable between 2 ports on the same switch, both ports would have to have BPDU filter enabled on them for that to be an issue though.

dominic.caron Fri, 11/16/2007 - 09:01
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Hi,


I've found that some device(soho router) filter bpdu. One of those is a wireless router made by...linksys!

m_zabetian Fri, 11/16/2007 - 10:15
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sounds like loop check your spanning tree

maybe you have no spanning tree vlan ...

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