Show port changes

Unanswered Question
Mar 7th, 2007

I know there is a way while on a switch to have a computer plugged into it, unplug the network cable then i can see which port changed its status from up to down. Can someone help me?

I have this problem too.
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Joe Clarke Wed, 03/07/2007 - 09:16

There are quite a few ways to do this. Perhaps the easiest is to watch the LEDs on the switch to see which one goes out when the cable is unplugged. If the switch is quite large, or you don't have physical access, you can connect to it via telnet or SSH, and watch for logging messages to appear when the cable is unplugged. This method may not work depending on how the switch is configured. For example, on an IOS switch, you would need to have the following configured under your interfaces:

logging event link-status

Then your telnet or SSH terminal would need to be monitored:

Switch# terminal monitor

Along the same vein are SNMP link notifications If you have an SNMP notification (or trap) receiver (network management server) you can configure the switch to send link up/down notifications to this server, and watch for the notification to come in when the cable is disconnected. Again, this may require additional configuration on the switch.

Finally, you could always capture the output of a command like "show ip int brie" (IOS) or "show port status" (CatOS) then disconnect the cable, and capture the same output again. Then compare the two to find the port that went down.

joeyrego214543 Wed, 03/07/2007 - 09:22

for the logging event link-status one will i have to have anything else configured? I have done so and unplugged a client plugged into a switch and nothing comes up.

Joe Clarke Wed, 03/07/2007 - 09:29

Like I said, you will need to make sure the current terminal is monitored with the "terminal monitor" command. You will also need to make sure you do NOT have "no logging monitor" in the config.

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