Some DHCP clients not picking up internal DNS server assignments

I have a strange problem that has just developed.

A few users (who get their IP via our DHCP server as do all our on-site clients) are not seeing or picking up the internal DNS server.

When I do an nslookup i get "unknown server"

When I manually assign the DNS server IP in their network setup all is fine

What could be causing this odd behaviour??

tracyprierNetwork AdministratorAsked:
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David Johnson, CD, MVPOwnerCommented:
have you added the dns server into the dhcp properties field?
tracyprierNetwork AdministratorAuthor Commented:
yep, always been there and its only a few users who are getting this
Muhammad BurhanManager I.T.Commented:
Give a try with deleting lease information in DHCP scope for those clients and then ipconfig /release and ipconfig /renew at client side.
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tracyprierNetwork AdministratorAuthor Commented:
Tried that, no fix.

I found that if I manually specify the internal DNS server under the PC's network settings it works fine.

I have ensured there is a DNS ptr record in the DNS server for itself.
tracyprierNetwork AdministratorAuthor Commented:
Further informaiton.

My PC lost internet connectivity so I did a nslookup command which returned a "server: unknown"

Did an IP release / renew then ran nslookup again and the DNS server is there.
Muhammad BurhanManager I.T.Commented:
so still the clients facing that same problem ?
tracyprierNetwork AdministratorAuthor Commented:
Yes same issue
Muhammad BurhanManager I.T.Commented:
please recheck the scope options in ipv4.
006 DNS server
015 DNS Domain Name
did they point to the valid DNS Server's IP ?
tracyprierNetwork AdministratorAuthor Commented:
Yes checked all that already.

This network is not new and the current DNS settings / server have been like this for over one year.
No changes have been made recently but this problem seems to have just appeared

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tracyprierNetwork AdministratorAuthor Commented:
Turned out to be a WAP with DHCP enabled.
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