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Strange network connection problem

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by pringles86

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Ok... I have a department who uses the network connection in a particular meeting room only once a week. It has been working fine for the past year or so. Then, when they tried to use it this week, it didn't work. They called me over and I did some testing.

I canceled out the possibility of it being the cable by plugging it into a known good port on the switch and using the same laptop they had used. It worked just fine. I then plugged the cable that was in that port into a different port in the switch, and it worked. I switched them, and the problem cable only worked for a minute or so, then stopped working.

Is there some way that the firewall or router is set so there can only be a certain amount of connections active at one time?

8 replies

by cg it

yes, there can be some way that only certain connections work....

need more information to make a suggestion.

by pringles86

It is a Cisco switch, that is all I know at this point. I will just have to ask them to call their network management people to see if it is a problem there.

Thanks.

by triathlete1981

have you tried a known good cable on the port in the meeting room? i kind of got a little confused with your port switching. sorry. it seems like you didn't isolate the cable as not the problem. you took cable A, which was connected in the meeting room and wouldn't work, physically walked over to your switch and plugged cable A into a known good port. it worked - then, yes, there is no problem with the cable. second, you took cable B, which was originally in the known good port on the switch, and moved it to a different port. cable B, which worked before the switch, now is no good for a connection.

if i understand that correctly, then you have a switch problem. if someone didn't mess around with your switches configuration and disable switches, or set up vlans so one port could not find your internal gateway, then you have a bad switchport.

first, make sure no one did mess with your switch. then, contact the manufacturer to find out how you can run diagnostics on the port. if that doesn't work, see if it's still under warranty, because i don't know any way to fix a particular switch port. maybe this is going out on a limb, but doubt there's anyone aside from the manufacturer of the switch who can do that. if under warranty, send the switch back for maintenance/repair.

if that's not a possibility, just ignore the port, and mark it as defective by putting in an empty rj-45 connector that taped up or something so everyone knows it's bad. and if that's no good, buy a new switch.

curiosity, what brand is it? if it's a cisco, then you could just run some commands in enable mode that will tell you if someone added the port to a vlan or if something else is amiss.

by pringles86

Thanks for your response, and sorry for making such a confusing and unclear post. You did understand for the most part. The only thing that I did not clearly explain was when I put cable A (meeting room) into the port it was originally in, and I unplugged cable B. Cable A then worked, then I plugged cable B back in, and cable A no longer works. It seems as though only 10 ports can be active at once.

It is a Cisco switch, but I do not have access to get into it to issue commands. They are part of the Supreme Court, so I guess it would have to go through them. I just wanted to see if I was missing an easier solution.

Thanks for the help

by cg it

Probably there's port security on the switch port plus VLANs.

If there is MAC address security on the switchport, then if you try to plug in another host, the switch will deny the connection.

Since you don't have access, you need to elevate the problem to the network engineer who handles the infrastructure.

by pringles86

Just strange that it would work for a minute then it would stop working...

Thanks for your help.

by cg it

if whomever configured the switch applied switchport MAC address security. The switch will automatically turn off [disable]the switchport when an unauthorized host connect to a port.

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