Weird Switch Issue : Incoming link drops when 3rd machine is connected

[superc0w]

Several Linux machines/servers need access to the internet in my workplace. Due to the lack of lan ports in my work area, I use a gigabit switch (DLink 1224T) to "split" the internet so that all these machines can get online.

However the incoming link from the lan port always goes down after a period of time. After some testing, I found that :

1) The incoming link drops when more than 2 machines are connected to the switch. When I connect a 3rd machine, the incoming link will go down, causing all 3 machines to be offline. Prior to that, the first 2 machines have no issues at all.
2) It doesn't matter which lan port I use for the incoming link, the issue remains
3) The link comes up again after about 5 minutes, only to go down again after a short period if more than X machines are connected.

I'm wondering if this is some switch configuration issue on my side or the IT side, or some weird Linux networking issue.

 

[Emerald]

how many computers are you running on that switch?

have you tried a different switch?

 

[thehelo]

what device is the gigabit Dlink switch plugged into. Sounds like a port security configuration on a cisco switch which causes the port to go into the err-disabled state when it sees more than 2 mac addresses on the port. This can be set to bring the port back up after a certain period of time.

Start your troubleshooting with the network device that the single ethernet connection comes from. Its probably a configuration issue on that device.