Sunday, July 20, 2008

AD site discovery

This post discusses the scenario where in an Active Directory with one site, that site is always returned as the client site, even if the subnet isn't recorded in AD. This is not necessarily the intuitive result, and I couldn't easily see this documented anywhere by Microsoft, hence the testing below.

The theory is that because there is only a single site in AD, all clients will belong to that site by default regardless of IP subnet. The converse is also true, in that if there is more than one site in the directory, then without correct IP subnets a client will be unable to determine its site.

To prove this theory, I created a site in the a 2003 AD lab and ran some tests:

  1. As soon as more than one site exists in the directory, if a workstation’s IP address is not part of a known subnet linked to a site, ‘null’ will be returned when querying the site a client belongs to.
  2. If only a single site exists, with or without the subnets in AD the client will return the first and only site as the current workstation site


  1. In the first test where the site could not be determined, the netlogon locator was still able to find and use a DC, but in a distributed environment it would more than likely not be the closest DC.
  2. This would almost certainly cause issues with SMS using AD site boundaries. As soon as a second site was added, any workstations in subnets that were not in AD would stop working as SMS clients.

Test process:

  1. Created a second site in the lab, two sites now exist, with no subnets
  2. Waited a minute or so, from an XP workstation: 'nltest /dsgetdc:domain' still returns ‘our site’ of default-first-name-site
  3. Restart netlogon on an XP workstation, same result ]
  4. Restarted the workstation
  5. nltest /dbflag:0x2080ffff
  6. net stop netlogon & net start netlogon
  7. Check netlogon and nltest, site name of null and nltest omits ‘our site’ from the output:
    find /i "site" c:\windows\debug\netlogon.log
    07/14 09:56:35 [SITE] Setting site name to '(null)'
    07/14 09:56:38 [INIT] SiteName (0) = (null)
    07/14 09:56:38 [INIT] CloseSiteTimeout = 900 (0x384)
    07/14 09:56:38 [INIT] SiteNameTimeout = 300 (0x12c)
    07/14 09:56:38 [INIT] AutoSiteCoverage = TRUE
    07/14 09:56:38 [SITE] Setting site name to '(null)'
    C:\Program Files\Support Tools>nltest /dsgetdc:domain
    DC: \\TESTAD1
    Address: \\
    Dom Guid: 3aa9ef9a-f1b4-4ce4-a85b-823b259c4919
    Dom Name: domain
    Forest Name: domain.local
    Dc Site Name: Default-First-Site-Name
  8. Deleted the second site
  9. reboot an XP workstation, check netlogon and nltest:
    find /i "site" c:\windows\debug\netlogon.log
    07/14 10:01:43 [SITE] Setting site name to '(null)'
    07/14 10:01:43 [SITE] Setting site name to 'Default-First-Site-Name'
    07/14 10:01:43 [INIT] SiteName (0) = Default-First-Site-Name
    C:\>nltest /dsgetdc:domain
    DC: \\TESTAD1
    Address: \\
    Dom Guid: 3aa9ef9a-f1b4-4ce4-a85b-823b259c4919
    Dom Name: domain
    Forest Name: domain.local
    Dc Site Name: Default-First-Site-Name
    Our Site Name: Default-First-Site-Name
    The command completed successfully 

Wayne's World of IT (WWoIT), Copyright 2008 Wayne Martin.

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About Me

I’ve worked in IT for over 20 years, and I know just about enough to realise that I don’t know very much.