DCLocator and Closest Site info

I’ve been doing some research to prepare for my upcoming first delivery of AD Troubleshooting workshop. The agenda of content includes DCLocator and Netlogon content. Hence this post.

For the real detail on dsgetdcname and details on the nltest /dsgetdc flags, please see http://msdn.microsoft.com/en-us/library/ms675983(VS.85).aspx.

I made a lab environment which consisted of a single domain forest and 1 x Vista and 1 x XP client. Here are my observations.

If the Vista client’s IP address is from a subnet known by AD, a Windows Server 2008 DC will provide the closest site info details as well. It does not do this for XP. Presumably other down-level OS editions are also not given this detail but I didn’t check.

Here is the LDAP filter one of the UDP based CLDAP ping performed by the Vista client.

Filter: (&(DnsDomain=adatum.com)(Host=ADTMCLIENT1)(DomainGuid={AEF3F962-37E0-D147-8611-D8CA1AAED85E})(NtVer=16:00:00:00))

And the response back from the Windows Server 2008 DC is as follows.

Frame: Number = 86, Captured Frame Length = 200, MediaType = ETHERNET

+ Ethernet: Etype = Internet IP (IPv4),DestinationAddress:[00-03-FF-0D-FA-00],SourceAddress:[00-03-FF-A5-9B-45]

+ Ipv4: Src =, Dest =, Next Protocol = UDP, Packet ID = 3904, Total IP Length = 186

+ Udp: SrcPort = LDAP(389), DstPort = 58266, Length = 166

+ Cldap: (CLDAP)Search Result Entry, MessageID: 1, Status: Success

- NetlogonAttribute: LogonSAMLogonResponseEX (SAM Response to SAM logon request): 23 (0x17)

- SamLogonResponseEx: ADTMDC1.adatum.com

Opcode: LogonSAMLogonResponseEX

Sbz: 0 (0x0)

+ Flags: 0x000013FD

DomainGuid: {62F9F3AE-E037-47D1-8611-D8CA1AAED85E}

DnsForestName: adatum.com

DnsDomainName: adatum.com

DnsHostName: ADTMDC1.adatum.com

NetbiosDomainName: ADATUM

NetbiosComputerName: ADTMDC1


DcSiteName: HQ

ClientSiteName: HQ

Unknown: Binary Large Object (7 Bytes)

+ Version: 0x00000015 NT Version 5 Client

+ LmNtToken: Windows NT Networking: 0xFFFF

+ Lm20Token: OS/2 LAN Manager 2.0 (or later) Networking: 0xFFFF

The italic Unknown: Binary Large Object (7 Bytes) has hex details corresponding to the following.

05 53 69 74 65 32 00


Here is the site topology created using the ADTD Visio tool.

AD Sites

Currently Netmon 3.2 with latest parsers decodes as above. Wireshark as of v1.0.5 did not decode this.

Please note that the above “Unknown: Binary Large Object (7 Bytes)” field is NOT available if the DC cannot see a subnet that the Vista machine belongs to. Netlogon.log on the client shows that the client did not use any try_next_closest_site flags. Yet the DC still presents the information. It can do this as the filter has a NtVer=16:00:00:00 string identifying the Client OS. XP for example would use NtVer=06:00:00:00. Hence a Windows Server 2008 DC will not respond with closest site info to them.

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