DNS cache problem (appears to be client side)

I provide IT support for several small to medium sized business.  One thing I've noticed is that with 2 of the larger clients - workstations will periodically suffer from what appears to corrupt DNS Cache.  This is only when resolving non internet hostnames.  Each client has several remote sites but this problem occures randomly on both WInXP and 7 workstations.  

Symtpoms: "I can't log into Exchange - it shows disconnecte" or "I can't access the AS400"
Solution: ipconfig /flushdns and ipconfig /registerdns

if I do an nslookup, the server resolves the hostname no problem.

I get 1-2 calls that require this fix per month but I can't find a single thing about this on the internet.

Advise anyone?
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I take it you have already reset the TCP\IP stacks and the winsock stacks on both of these machines?
Dirk KotteSECommented:
if ipconfig /flushdns solves your problem...
you can display the local dns cache with
ipconfig /displaydns
save the result and compare it with the result after /flushdns

if ipconfig /registerdns solves your problem...
are the DNS entries for the client at the DNS-server (forward and backward) correct before calling /registerdns?
You cuold always just treat the symptoms (not ideal) by putting:

ipconfig /flushdns

into their login script.


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GDavis193Author Commented:
Still same problem - I've reset TCPIP and Winsock/2 and I still have users who occasional don't resolve a hostname.  ipconfig /displaydns shows no entry for the local hostname but NSLOOKUP resolves it just fine.

Pulling my hair out here....
Dirk KotteSECommented:
what do you mean with "I still have users who occasional don't resolve a hostname"
thes user-devices cant resolved by nslookup (forward/backward) or these clients have problems resolving (different?) hostnames (local/ping/nslookup/../ fqhn or netbios-name?)

the own systemname should not be present within the local dns-cache.
are the problem-clients able to resolve the "not working" hostames with nslookup - if not please post the answer message.

GDavis193Author Commented:
Symptom: User can't connect to Exchange, timeforce (their web based time clock system) etc.

Solution: ipconfig /flushdns and /registerdns

Troubleshooting shows this:  For some reason, hostnames on the LAN are no longer resolving.  It's not ALL hostnames (servers in this example), sometimes it's just one or two.  When this occurs, running an NSLOOKUP brings up the DNS server and it resolves the hostname no problem.  The clients DNS cache shows missing IP entries for the hostname.

So yes, nslookup works but ping fails.  The clients 'forget' about these hostname/IP resolution randomly.  
Dirk KotteSECommented:
do you use working with the "hosts" file at these workstations?
there are known buffer problems within Win2003 and possible Windows XP/7 also.
are there "many" entries within the DNS-cache?
you could edit the host file to include a static mapping, that is a workaround but not a fix. Are the servers multihomed?  Do you have offline files enabled on the clients? Try turning this off.When a client is affected what ip address is listed when you ping the mail server? Are your clients DHCP? Where are they getting DNS? Check the DNS server itself. Do you have the DHCP server offering a WINNS server as well?
GDavis193Author Commented:
I would prefer to not edit the HOSTS file.  

Yes there are man entries in the DNS cache.

Offlinefiles = no

I did notice one thing - they have public DNS names listed for the same internal hostnames.  I know I didn't explain that well so let me clarify.

server hostname: mail.domainname.com
internal IP:
nslookup resolves mail.domainname.com to

They also have public DNS pointing to a puiblic address (ie 67.137.xx.xx) so:
A record = mail.domainname.com 67.137.xx.xx

when the local DNS cache fails, when i ping mail.domainname.com I get the public IP.  So for a week it was resolving the internal IP address as desired but at some point it failed and resolved the public IP and kept it.  This also explains why hostnames with NO public DNS record simply fail to resolve anything.

For some reason they are losing connectivity to the internal DNS server and when the cache expires it's unable resolve properly?  Hmm.... is there a way to have the local DNS service refresh the internal DNS cache more often?

GDavis193Author Commented:
I forgot to add: DHCP for IP and DNS.
no WINNS server
Dirk KotteSECommented:
why you dont use wins?
our domain-guys mostly install wins because it is simple, quick (and should solve your problem)
ok thats only a workaround ...
do you have the primary dns server hard coded to an external server? You should have the replication partner the first entry then the loopback as the secondary

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GDavis193Author Commented:
Problem resolved by discovering a Name server entry in DNS pointing to an old decomissioned server.  Removed it and it appears to bo working thus far.

Points given for effort.
GDavis193Author Commented:
Appreciate the help - answered my oqn question.
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