I got the following error on a Domain Controller:

During the past 4.22 hours there have been 114 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.

'%SystemRoot%\debug\netlogon.log' has lots of errors like:


In my Active Directory 'Sites and Services' The domain controller question is in a site that doesn't correspond to the geographic location (There isn't a 'site' for this location), and the IPs in the netlogon.log are not listened in the 'subnets' in Sites and Services.

  • Is this problem?
  • What is Sites / Services for anyways?
  • What would be the implications of creating sites, adding all the subnets that are actually in the network, and moving the Domain Controllers to the 'Site' under sites and services?
  • Are Sites and Services the same on all Domain Controllers (Replicated) ?

Please forgive my AD ignorance...


Sites allow you to relate physical location to particular areas of the network and group them together. Say you have a site in New York that uses one subnet, a site in Boston that uses another and a final site in San Fransisco on another. Using sites you can specify what Subnets relate to what sites and also the cost of communication between sites. So in this example you would specify a lower cost between Boston and New York, than you would between New York and San Francisco. This way, if your DC in New York goes down, clients in that subnet will use the cheapest link and attempt to connect to the Boston DC, rather than picking the first DC they can find, which may be San Francisco, all the way on the other side of the country.

Sites also allow you to configure AD replication more efficiently, using the most cost effective and fastest routes to replicate your topology.

If you have a machine that is not in a site, as your error suggests, its not going to cause a massive problem, but its inefficient. When looking for a DC, this machine is just going to get the first one it finds, that could be one in the same office, or it could be 5000 miles away.

By creating sites that map to your networks subnets and configuring links you will make your network more efficient. That said, if you are only in a single office, with no remote sites, then your best just putting everything in the default first site and leaving it at that!

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  • I also found once that an exchange front end server didn't work until I added the subnet. Does that sound possible, or did it just happen to start working at the same time? – Kyle Brandt Aug 7 '09 at 18:20
  • Its always best to put servers in a site, but I can't think of a reason why Exchange wouldn't work if it wasn't, but doesn't mean there isn't a reason! – Sam Cogan Aug 7 '09 at 18:23

sites are used to map your infrastructure. I wouldnt worry about the log its for information only. however if you do use sites client will use autosite to find the nearest DC.

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