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How to find loops

asked 2021-08-10 21:10:58 +0000

pperry gravatar image


What do I need to search for in my packet capture to see if there are any loops in my network? I have certain rooms in my office building that do not have network connectivity, but they have PoE. The switch that they all lead back to is showing no activity lights, except for the one that is getting the internet connection from. I have changed cables, toned the wallplate port to the patch panel, and I have completely replaced the switch, with a known working one, and still cannot get network connectivity.

Any help would be greatly appreciated.

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How do you related 'loops' to 'no network connectivity'?

Jaap gravatar imageJaap ( 2021-08-11 09:34:20 +0000 )edit

I have discussed this with other people and they suggested that this might be caused by a cable being plugged from the switch to the same switch. I thought that was called a loop. If it's not please let me know what it is called, so I can correct myself in the future.

pperry gravatar imagepperry ( 2021-08-11 11:58:28 +0000 )edit

It could be that the switch does port isolation of ports it finds in a loop. The other ports should work normally, which according to your report is not the case. So either all ports are looped, or something else is going on.

An approach to find out is to disconnect all downlink ports of the switch and plug them in one by one. Note which port works, which don't, then start to plugin multiple ports and seen if ports start to get isolated, if any. If you've got a decent switch you may also want to access the management interface and see what it reports on the port status.

Jaap gravatar imageJaap ( 2021-08-11 14:59:02 +0000 )edit

I have tried that with both switches, and none of them still work. The main switches that I need to get into, say I need Java installed, and I've tried installing Java, and used IE, and Edge. Chrome will not let you use Java. I'm out of ideas on what could be causing this.

pperry gravatar imagepperry ( 2021-08-11 15:08:37 +0000 )edit

I was finally able to get into the switch by using Edge with CheerpJ extension. It shows that only the input is working, and that nothing is plugged into the other ports, even though every port has a cable plugged in except for about 2 of them. What are the chances that a whole patch panel would go bad?

pperry gravatar imagepperry ( 2021-08-11 15:24:26 +0000 )edit

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answered 2021-08-12 07:36:38 +0000

BigFatCat gravatar image

updated 2021-08-12 07:42:47 +0000

Does the wire toner include an Ethernet cable tester? That would save a lot of time to determine if there is an open. If you think the patch panel is bad, take one of the connections and bypass it. If you have a laptop, connect it at different points with either a straight or crossover cable to verify where the connection is good at.

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Asked: 2021-08-10 21:10:58 +0000

Seen: 4,886 times

Last updated: Aug 12 '21