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We have a Server 2008 R2 Primary Domain Controller that seems to have amnesia when it comes to working out what kind of network it is on. The (only) network connection is identified at startup as a 'Public Network'.

Yet, if I disable and then re-enable the connection, it happily figures out that it is actually part of a domain network.

Is this because AD Domain Services is not started when the network location is initially worked out?

This issue causes some headaches with Windows Firewall Rules (which I am more than aware can be solved in other ways) so I am mostly just curious to see if anyone knows why this happens.

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Please, repeat with me: "there is no Primary Domain Controller, and there has never been since Windows 2000". –  Massimo Feb 21 '12 at 20:35
My sincere apologies. Web Developer having to look after a Windows Network! –  MattR Feb 21 '12 at 20:40

3 Answers 3

up vote 8 down vote accepted

Do you have a default gateway on that connection? Does it reply to ping requests?

Windows uses gateways to identify networks; if it doesn't have a gateway configured, or if it can't succesfully ping it, it will not be able to identify the network it's connected to and will assume it's a public one.

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We do - The gateway is also a Server 2008 R2 Machine running Forefront Threat Management Gateway, which the DC can ping. –  MattR Feb 21 '12 at 20:39
Does your DC have more than one NIC installed and in use?? –  John Homer Feb 21 '12 at 20:43
Nope, just the one. –  MattR Feb 21 '12 at 20:45
Got it - inadvertently had IPv6 turned on so it must have been trying to find the gateway through v6. Turned that off and it works fine. –  MattR Feb 21 '12 at 22:12

Wheter the network of a domain controller is classified als domain network doesn't depend on the gateway configuration.

The behaviour of a false network classification can be caused the NLA (network location awareness) service starts before the domain is available. In this case the public or private network is choosen and not corrected afterwards.

How to check if this fault situation is given
When the domain controller after rebooting is in the public network, restart the NLA service or disconnect / reconnect the network. The domain controller should be in the domain network afterwards.

How to solve it
It may help to set the NLA Service to delayed start. Better, check why the domain needs long to be present. It seems that the domain needs longer to start when there are multiple network cards.

When it doesn't help
When neither speeding up the loading of the domain nor the delay of NLA help and the error is caused by the long loading of the domain (look: "how to check..."), then there are some more things that can be done.

  • Restart the NLA service manually after every reboot
  • Write a skript for restarting it an run it with the scheduler (dangerous)
  • Shift the loading of the NLA service to the end of the service starts, changing the load order in the registry (dangerous)

One more cause can also be when the domain controller has two or more IPs configurated (on the same or on other network cards) and the additional networks aren't configured in the DNS.

Reproduction of the behaviour
On a test domain controller (single DC!) I deleted the default gateway entry and set the DNS Server to delayed start. Doing this the domain needed long to get loaded and the network was classified as public. After disconnecting and reconnecting the network cable, the network was classified correctly as domain network.

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I've seen similar behavior standing up a 2008 R2 AD server. The thing that got me was having more than one NIC enabled, even though it wasn't in use. Once I disabled the unused NICs and rebooted, the problem went away.

The exact windows feature you're up against here is called NLA. I don't know enough about it to claim to be an expert, but I know there's some interesting information out there on the intertubes about how it all works, or is supposed to work.

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