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VLAN Slow Down


Guys I have a VLAN that is totally slow on the internet, I am not sure if is contributed to the power outage that we last Friday night, but I notice the issue Monday morning.

I checked everything I can possible check with the core switch, I have maybe about 15 dell switches, and about 3 cisco access switches on that vlan I am not sure if one of them are just sending broadcast or what.

I am keep seeing use wireshark to troubleshoot, but what am I suppose to be capturing? and how do I tell if it is just a bad switch or a computer that is slowing me down?

I configured SPAN on the core for the interface that is assigned to the vlan, and going to run wireshark but not sure what to filter once I capture it.

Also if you have more troubleshooting tips on this issue let me know, this is day #5, and I might now have a weekend, I opened a case with Cisco last night to check the core, not sure how much they can be with this kind of issue.



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VLAN Slow Down

Hello Chad.

There are several possible reason why your switch/vlan could be having high latency issues or slow performance.

- Duplex/Speed mismatch.

- Output drops.

- Interface erros.

- Spanning-tree loops.

- High CPU.

Check you both uplinks and access port for possible duplex/Speed mismatch.

     - Most of the times, the show log is enough to realize there are speed and duplex problems. You can also run the command show interface to check for specific interfaces.

Check for both uplinks and access ports for possible output drops / input errors

     - Output drops are equal to packet loss, when you experience packet loss you will also notice that connectivity problems, lots of retransmissions, acknowledgents, resets .... etc (in wireshark) Check for the output of the command Show interface counters errors.

Check for spanning-tree loops.

     - The best way is to enable mac-address notification mac-move from the global configuration. Then take at look at the show log for possible mac-flapping, host learning messages.

Check CPU utilization.

     - Commands like show process cpu sorted | ex 0.00 helps in this case.


Wilson B.

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