Connections From Machines That Don’t Map to Sites?

KB ID 0001635


I was troubleshooting some replication issues for a client, and carried out a dcdiag on one of their domain controllers, and saw this;

 Starting test: SystemLog
A warning event occurred. EventID: 0x000016AF
Time Generated: xx/xx/xxxx xx:xx:xx
Event String:
During the past 4.21 hours there have been {xxx} connections to this Domain Controller from client machines whose IP addresses don’t map to any of the existing sites in the enterprise. Those clients, therefore, have undefined sites and may connect to any Domain Controller including those that are in far distant locations from the clients. A client’s site is determined by the mapping of its subnet to one of the existing sites. To move the above clients to one of the sites, please consider creating subnet object(s) covering the above IP addresses with mapping to one of the existing sites. The names and IP addresses of the clients in question have been logged on this computer in the following log file ‘%SystemRoot%\debug\netlogon.log’ and, potentially, in the log file ‘%SystemRoot%\debug\netlogon.bak’ created if the former log becomes full. The log(s) may contain additional unrelated debugging information. To filter out the needed information, please search for lines which contain text ‘NO_CLIENT_SITE:’. The first word after this string is the client name and the second word is the client IP address. The maximum size of the log(s) is controlled by the following registry DWORD value ‘HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters\LogFileMaxSize’; the default is 20000000 bytes. The current maximum size is 20000000 bytes. To set a different maximum size, create the above registry value and set the desired maximum size in bytes.


On the DC in question, Windows Key+R > %Systemroot%\debug\netlogon.log > OK > There’s you missing subnet!

Missing AD Subnet

Go to Active Directory Sites and Services, add the missing subnet, and allocate it to the correct site.

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Author: PeteLong

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