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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.

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Is it a Laptop? Could it be the powersave settings? –  Ximon Mar 4 '10 at 23:40
    
oh cabled so prob not. –  Ximon Mar 4 '10 at 23:41
1  
renewing a DHCP lease does not cause any sort of disconnection. –  user23307 Mar 5 '10 at 3:10
    
does the network cards are the same brand? If it's the case they could use the same driver... –  fluxtendu Mar 5 '10 at 7:09
    
Different brand; new one is a Belkin card with a Realtek chip. Old one is an on-board Atheros chip. –  nbolton Mar 5 '10 at 18:18

1 Answer 1

up vote 1 down vote accepted
+100

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.

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+1 Lather, rinse, repeat. Anyway, I think you're right about the DHCP client not being able to contact the DHCP server; but I wonder why it occurs for this computer only? The routing is just default... Unless some app has changed it somehow, hmm... –  nbolton Mar 15 '10 at 13:45
    
Does the trouble exist if you boot into Safe Mode with networking enabled? –  goblinbox Mar 16 '10 at 23:01

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