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We have a server with a static IP, let's say x.x.2.5. We have several WinXP (but not all) that will occasionally resolve the hostname to x.x.1.59 (x.x.1.x is the local subnet).

The DHCP range in the router is set to x.x.50-199 and the router has issued a lease for 1.59.

It is theoretically possible that some host with the same hostname is out there. It responds to ping but does not appear to have registered itself with our Windows DNS servers (no entry for 1.59), so I don't think that this is the case.

DNS for the 2.5 server is static and it only appears one time (no other entries for this server appear).

On the affected PC, if I do:

ping THEHOST

I get 1.59

if I do

nslookup THEHOST

I get 2.5

So it appears the local cache is somewhat fubar. If I restart the XP machine, it picks up the correct IP address and all is well. Failure is intermittent and not reproducible after reboot.

Our local Windows admin is stumped and so am I (but I'm not a Windows admin, so that is not surprising). Any way to track down this crazy IP? When it happens again, what should I check?

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2 Answers

I would check the hosts file on the affected server:

%SYSTEMDRIVE%\windows\System32\drivers\etc\hosts

And look for a rogue entry for THEHOST

The reason is that nslookup ALWAYS uses the default DNS server for its resolution, but Ping goes through the normal Windows method, which checks the hosts file before it checks the DNS, and this may be getting cached.

The other avenue is to do an ipconfig /flushdns and see if it resolves correctly after that.

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When Windows XP attempts to resolve NETBIOS names which is what you are using if you don't give a full DNS name with suffix it goes through the following resources in this order

  1. NetBIOS name cache
  2. WINS server
  3. B-node broadcast
  4. LMHosts File
  5. Host file
  6. DNS server

Using nslookup skips right to number 6, which is probably why you don't see the problem when you use nslookup. Cache poisoning and a rogue WINS server seem unlikely, and if the problem is not reproducible on reboot then it is not a HOST or LMHOST file problem. That leaves b-node broadcast as the most likely source of the problem. I would guess that you have a machine on the same network segment as the affected hosts that has the NetBIOS name THEHOST. One way to tell if it is a netBIOS problem is by pinging THEHOST.DOMAIN and seeing if that makes the problem go away, if so definitely NetBIOS, if not, then you've got a DNS problem.

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you can memorise the order by using this phrase: "can we buy large hard disks" Cache, Wins, broadcast, Lmhosts, Hosts, Dns –  DmitryK Jan 6 '10 at 14:28
    
Interesting, I'd never heard that before. Somehow I managed to twist my brain such that the order actually makes sense which is just plain wrong. –  Catherine MacInnes Jan 6 '10 at 16:54
    
New update: ping THEHOST gives wrong IP; ping THEHOST.THEDOMAIN gives "ping request couldn't find host" error –  Matt Rogish Mar 19 '10 at 13:29
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