Why does my ethernet connection keep re-connecting, only with Windows?

Question

I'm using Windows 7, and I have several computers on my network. For some reason, the network connection keeps disconnecting and immediately re-connecting. Infact, it may just be refreshing the DHCP lease... but I'm not sure.

I've tried changing the network card, and ethernet cable, but the issue is still happening. I can only imagine that the issue is with the ethernet switch, but this doesn't happen on my other desktop which uses the same ethernet switch.

Any ideas?

Update:

This is making applications like Skype and SSH clients unusable, as when it reconnects, everything else disconnects.

Answer 1

Here's what I think is happening: DHCP clients attempt to renew the lease about halfway through the life of the lease. A DHCPREQUEST to renew goes to the DHCP server that granted the lease, and if the lease is extended, the lease expiration time is adjusted to reflect this. There is no ipconfig /release, which drops the assigned IP address, involved, so there is no interruption in connectivity. If, after some interval, the DHCP server which granted the lease cannot be contacted, DHCPREQUESTs are sent with no server specified, and if no response is received before the lease period ends, the lease expires. At lease expiration, an ipconfig /release occurs, dropping the assigned IP and interrupting connectivity. A broadcast DHCPDISCOVER request is made for any listening DHCP server, and when a server responds, a new lease is requested (ipconfig /renew does this if no lease is active). When a new lease is granted, connectivity is restored.

I think your problematic machine for some reason can't reach the assigning DHCP server, and so cannot receive a renewal. At lease expiration, connectivity drops, and a broadcast DHCPDISCOVER request is issued. The DHCP server hears this, responds, and a new lease is negotiated. Lather, rinse, repeat.

I predict that the connectivity interruption changed in sync with your changing the lease interval. If it did not, my theory is wrong, and you can stop reading.

If the loss of connectivity event happens at the end of a lease interval, we've got to figure out why the DHCPREQUEST renewal is not getting to the DHCP server. One possibility is something wrong with the routing table on that machine. Use route print when the machine is connected, and ipconfig /all to show the lease details.

Answer 2

I'd swaps ports on the switch with a machine you know hasn't had any issues.

If you experience issues on the other machine you'll know it's the switch and not the machine.

Could just be a faulty port

Answer 3

Since you've replaced your NIC and Ethernet cable, it has to be a bad port on the switch.

Answer 4

Update your NIC drivers in Windows. Find out what chipset it uses, go straight to the NIC vendor's website (or the NIC chipset vendor's website), get the latest build of the driver, and use the Device Manager in Windows to update the driver by hand.

I second (and upvoted) @Ian C's suggestion. It could be a design flaw with that model and similar models of switch, as the vendors of low-end gear generally either buy gear from a small handful of OEMs, and they generally tend to just implement the IC vendor's reference design (meaning if they use the same Ethernet switching chip inside, they'll basically be the same design internally, with the same bugs and the same behaviour).

Try a totally different switch -- score a used Cisco switch off eBay for ~$150, as they're basically bulletproof and are high-performance (even a 5-year old Cisco switch will outperform a $50 cheapie switch made last year).

Answer 5

Infact, it may just be refreshing the DHCP lease... but I'm not sure.

Generally, you can check this out, just to exclude the chance it happens because of DHCP. The output of ipconfig /all contains detailed data about the DHCP lease: when the IP address was assigned and when will it expire. An accidental typo in the config file of the DHCP server can lead to IP addresses being assigned to very short time intervals, which is not normal.

But since you write that this doesn't happen on all computers, then this is probably not your case. The issue described above would affect all computers that get IP addresses from the same DHCP server.