I currently have an XP client keeps picking up and old IP address for a former subnet. IPCONFIG /RELEASE and /RENEW it still picks up the old address. I saw this exact same behavior with Vista two years ago, only they were on wireless and this XP machine is on a wired connection. So here is my layout:
DHCP Servers: DHCP01 (win2k3, hosts VLAN01 and VLAN02 addresses) and DHCP02 (Solaris 10, hosts only VLAN03 addresses)
VLANS: VLAN1 (default), VLAN02 (restricted), VLAN03 (SunRay thin clients)
Router: One Layer3 switch with interfaces on each VLAN
Clients: XP01 (XP, sp2), VS01 (Vista, no sp)
XP01 is a fresh install, no windows updates other than sp2. It was accidently plugged into a port that is in our thin client vlan (VLAN03) and recieved an address for that subnet (10.10.208.*). This vlan does not route to the internet so we noticed rigtht away and changed it over to a port for the default vlan (VLAN01, 10.10.1.*). However it maintained the ip address from the thin client vlan (10.10.208.26). We tried to do a /release (ip went to 0.0.0.0) /renew, but it still picked up the old address. We unplugged it for 5 mins and reconnected it, we rebooted, still came back to the VLAN03 address. We turned it off for 2 days, let the lease period expire, still comes back with the VLAN03 address.
I saw this behavior two years ago with some VISTA laptops. I was setting up our new wireless system. I setup the GUEST SSID to be in the restricted vlan (VLAN02) subnet (10.10.64.x). After a few days of running it I found some problems with that VLAN config, so I changed the GUEST SSID to be in default vlan (VLAN01). At the time all of the XP machines picked up the correct new address (10.10.1.x) but the Vista machines kept picking up the resctricted subnet addresses (10.10.64.x). I created a new SSID called USERS and pointed it to the default vlan. No problem, the Vista machines picked up the correct address (10.10.1.x) but when they used the GUEST ssid they still picked up the wrong address (10.10.64.x). I figured out that if I turned off the DHCP scope for the restricted vlan (10.10.64.x) and did a /reliease /renew that it finally moved into the correct IP scope. I could then turn it back on and the machines would continue to function correctly in the default vlan. Eventually I fixed the problem with the restricted VLAN and moved the GUEST ssid into VLAN02.
What I'm pretty sure what is happening is that XP and Vista cache their old DHCP assigned addresses. Then when they come up they send an UNICAST dhcp request and ask if they can use their old adderss. The server responds with "sure, it's still availible" and so the client keeps using it. The router doesn't update the correct field because it is a UNICAST packet, the server doesn't know/care where the request came from and simply says, yes, it's available. The client has no idea it's in a different VLAN. This behavior makes SOME sense for the wireless connection but make NO sense on a wired connection.
Is there anyway to block XP and Vista from asking to use the cached address but instead send a full, normal DHCP request?
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Try this:
Block Negative Entries
If you want to block cache Negative Entries in Windows XP you need to add a new DWORD to the following Registry key
Note :- Before doing any changes to the registry please take a backup of your registry
HKEY_LOCAL_MACHINE\SYSTEM\
DWORD: MaxNegativeCacheTtl
Value: 0
@qtworek I know they are getting the wrong server. The router is setup with a dhcp helper for vlan01 and vlan02, but vlan03 isn't. This is because that server is on the same subnet as the thin clients so I only want it to host addresses for it's own subnet. The problem is that the client isn't performing a normal DHCP request (which would be relayed to the correct server) but it is instead sending a UNICAST request for it's previous address.
@MagicFarmer This would fix it for this one machine, but this happens too often with other machines. Most of the time our PC's don't change VLANS, but some do, I can't afford to go around to everyone's PC to do this reg hack in order to prevent it in the future. This behavior didn't used to occur, anyone seen something from MS on it?
I believe the main problem with my Vista machines was that I was using a "SuperScope" on my DHCP server. I never did figure out the problem with the SunRay thin clients, but we moved on by simply turning off the offending server temporarily while the clients came up. This will not prevent the issue in the future, but perhaps we will pay better attention to which VLAN we plug it into from now on.
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by: gtworekPosted on 2009-11-04 at 10:16:33ID: 25742139
Did you check (i.e. with ipconfig /all) your PCs are obtaining addresses from the right DHCP server?