DC won’t DC anymore

30th April 2026

Uncategorised

Had a Windows Server 2016 DC acting strange.

Symptoms:

ping successful, DNS all correct

Firewall is off, AV is disabled

browsing any share including NETLOGON fails

DC thinks tcp 445 is listening

PS C:\share> netstat -ano | findstr :445
TCP    0.0.0.0:445            0.0.0.0:0              LISTENING       4
TCP    10.10.5.11:26029       10.10.5.112:445        ESTABLISHED     4
TCP    [::]:445               [::]:0                 LISTENING       4

Test-NetConnection nfgserver -Port 445 -InformationLevel Detailed
WARNING: TCP connect to (10.10.5.11 : 445) failed

ComputerName            : nfgserver
RemoteAddress           : 10.10.5.11
RemotePort              : 445
NameResolutionResults   : 10.10.5.11
MatchingIPsecRules      :
NetworkIsolationContext : Private Network
InterfaceAlias          : Ethernet 2
SourceAddress           : 10.10.5.104
NetRoute (NextHop)      : 0.0.0.0
PingSucceeded           : True
PingReplyDetails (RTT) : 0 ms
TcpTestSucceeded        : False

Fix:

reg add HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters /v DisableStrictNameChecking /t REG_DWORD /d 1 /f

net stop lanmanserver

net start lanmanserver

ODD:

the server was imported from Hyper-V, it has a ghost network adapter (greyed out), was this InterfaceAlias?

no reverse DNS, eventually created zone