I'm struggling with a dhcp problem at work and can't seem to find a solution. I'm not sure if you can help me but I thought I could give it a try, as I have the feeling I tried almost everything in my power aha!
Here's the thing. There are those four computers, which are basically exactly the same as any other computer in our place. Every 4 hour, connection drops. It happens every day and started a few weeks ago. There wasn't any change on our side: still the same server, still the same switch. We even changed one computer by a new one and the problem still occurred.
What I understand here is that dhcp client tries to renew the lease after, say, 2 hours and 3 hours: lease isn't renewed and at the end connection drops. A few seconds later, computer broadcasts a brand new request and gets a ip address.
We know that:
- Our dhcp lease lasts 4 hours.
- We have one dhcp server on this location.
- The dhcp pool has got PLENTY of addresses available.
At this point we tried different things, including setting a reservation in dhcp server and see what happens. I don't know yet if that solved our problem. Still, I would like to know what caused that.
Any thoughts on my issue? Thanks!
Update
Sorry I didn't answer sooner. IP reservation didn't work, as I expected. Something during the renewal process fails at some point.
I'm going to dig on those leads you gave me. I can look up on switches and see what is going on there, but my rights on dhcp server are much more limited.
I will try to give you some update as soon as I can. Wireshark may help: I'll launch it this afternoon on a client, at about the time of expected disconnection, see what happens.
Update 2
Hi guys.
Sad to say we didn't find anything relevant.
Users have had this problem for a few months and they already have been very (…) very patient. I really can't ask them to wait any longer.
So, static ip address it is. That's the only workaround I have. I keep my fingers crossed hoping that this issue won't spread to other workstations.
Thank you guys for your help!
Best Answer
This sounds like that the server running DHCP has had its firewall changed somehow so that DHCP renew packets do not reach the DHCP daemon properly. Therefore the renewal fails and the clients have to initiate the "I am a new device" process to get a new network address.
Getting the initial DHCP address is done via UDP, but TCP is also used with DHCP some time. So, make sure you can reach your DHCP server at port 67 with both TCP and UDP.