DC Server 2012 DNS/Internet issue

Background: I have a client who has a DC that was converted from 2008 to 2012R2. the 2008 server is still active on the network, but was demoted. the 2012 server is the DC and runs the DNS. The 2008 server that was the DC still runs the DHCP. There were issues during the conversion- but the conversion happened about 5 months ago. to get the conversion to work the regedit to set burflags d4/d2 had to be done. once that was done the conversion did complete successfully. no issues up until a few weeks ago.

Issues: The 2012 server could not get to the internet about 90% of the time. the other 10% of the time it will work fine, until the browser is closed and once re-opened it doesnt work. Page cant be displayed message. Also the 2012 server can not access file shares on the 2008 server unless you browse to it by ip address.

When we add the A record for the 2008 server to DNS in appears and successfully adds but in just a couple minutes it goes away? like it is auto deleted?

We decided to change Nic's on the 2012 server and when we disabled the nic, we looked at DNS and the 2008 server had showed up, but as the ip address of the 2012 server? 192.x.x.5, the 2008 server used to be the .5 address when it was the DC, but it was changed when the new 2012DC was installed. we changed it to .7 and made the 2012 DC .5 address?

Ran dcdiag on the 2012DC and there are all passes with the exception of the System log and it has some odd errors. referencing Kerberos and Ip addresses and the 2008 server name. I'm not sure why that would be showing in the syslog on the 2012 server?

I'm terribly stumped at the issues...It doesnt seem to be affecting workstations at this point but something is definitely amiss. I doubt there is a silver bullet for this situation but welcome feedback, questions, links and assistance! Many Thanks

Update: We changed to a different NIC on the 2012 server and assigned the same static IP address and now internet has worked longer than it has in about 3 weeks. still can not access file shares on the 2008 server from the 2012 server. and the A record on the 2008 server still is not retained.
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Dirk MareSystems Engineer (Acting IT Manager)Commented:
Your Server 2008 is it still running DNS?
You should check the DNS server properties that the correct network adapter is listening.

Also on your new server do you have your ISP public DNS ip configured for Forwarders?

350ztnAuthor Commented:
DNS is installed on the 2008 server but the service is disabled. the 2008 server is running DHCP.

Yes the ISP is in the DNS forwarders on the 2012 server. As of this morning the 2012 server is still getting to the internet after we changed NIC's.

The issue now is that it can not resolve the name of the 2008 server. I have checked the A record in DNS and the ip address does not exist for the 2008 server. If I add it, it is somehow automatically removed a few minutes later.
Dirk MareSystems Engineer (Acting IT Manager)Commented:
Your 2012 server where is the NIC pointing to for all DNS?

Your DHCP what DNS IP is it pushing out to clients?

Is this issue only between servers or between workstations and 2008?

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350ztnAuthor Commented:
Only between servers. DNS on the 2012 DC is pointing to itself

Dhcp is pushing the ip of the 2012 server. .5
Dirk MareSystems Engineer (Acting IT Manager)Commented:
Your Server 2008 NIC where is it DNS pointing to, the new 2012 server? Is their any reason why the 2008 server is still DNS server after demoting it from domain controller?

try the following..
On your Server 2008 (warning this will flush and reset all ip information)

ipconfig /flushdns
nbtstat -R
nbtstat -RR
netsh int reset all
netsh int ip reset
netsh winsock reset
Reconfugire IP addresses and go to advanced and to DNS at the bottom and Domain suffix and click register dns and run
ipconfig /registerdns

350ztnAuthor Commented:
2012 is DNS and DC server. 2008 server was the DC but has been demoted. 2008 has DNS service disabled. 2008 is still serving DHCP.
Dirk MareSystems Engineer (Acting IT Manager)Commented:
Is 2012 pointing to itself for DNS?

350ztnAuthor Commented:
Yes. And the 2008 server is static ip and DNS is pointing to the 2012 server.

This issue only exists between servers as far as I can tell.

Workstations can browse the 2008 file shares by server name resolution. The 2012 server can only browse it by ip.
Dirk MareSystems Engineer (Acting IT Manager)Commented:
Open DNS Manager on Server 2012, expand Forward lookup Zone and Your domain name..
Right Click your domain name an click properties. Go to the name servers Tab,

Is the Server 2008 box listed and is the IP correct with only one entry?

350ztnAuthor Commented:
Found out the issue was an incomplete migration of AD and some roles were still active on old DC. removed all roles, decomissioned and system working

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350ztnAuthor Commented:
resolved on my own
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Windows Server 2008

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