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How clients receive domain controller list?

colesy
colesy asked
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Medium Priority
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Last Modified: 2012-08-30
I am looking for an explanation on how this works to better understand how clients and domain controllers interact. .  In active directory clients are able to contact a domain controller. When a client is part of a site they will get a restricted list of domain controllers. How does this actually work? I am interested in how it works even down to the protocol level. Any help would be greatly appreciated..

Thanks!
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I can give you a high level..  Much of this is dependant on AD Sites and Services.  The Windows 2003 administrator should define thier network based on well connected network subnets.  well connected equates to LAN speed.  Anytime a WAN link is introduced to the network, a NEW AD Site should also be created.

In this way, the administrator carves out physicall sites comprising of the network.  For example:

NEW York:  Site 1

10.10.10.0
10.10.11.0
10.10.12.0

California:  Site 2
20.20.10.0
20.20.11.0

Florida:   Site 3
30.30.10.0

In Ad Users and COmputers, the administrator will create 3 sites and assign the appropriate subnets.  This is very important to AD replication and how the clients "talk" to the domain controllers.  The administrators will also move the DC's into the proper sites.  

When a user logs in and "talks" to active directory, the local IP address of the client is taken into account.  The local IP is related to a subnet... this subnet is cross references with AD Sites and Services.  From here, it is possible for Active Directory to determine what physical Site the client belongs to... furthermore, the client can be directed to domain controllers that also exist in the same site.

In this way, communication is localized.  

Now, I will explain this in binary:

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Thank you,

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Commented:
Hi,

Not much to add, great explaination,  NJComputerNetworks even though I slightly disagree with your binary interpretation, especially in line 24 where you probably meant

1110101011010001101111100001111110001111000101010100011101010010110100101110101010100101110101001011010101010011010101110101010010101011101010

But of course I can be wrong, I only took binary as a third language ;o))))

Some humor never hurts, especially when it comes to being serious ;o)

Cheers
Commented:
HAHAHA, seriously guys...

The client queries the configured DNS server, preferably the DNS server on the interface that matches the DNS domain name the computer is a member of.

The client constructs a very specific DNS query for specific SRV (Service Location) records that return the name and IP address of a global catalog, a domain controller or any other service in the site.

For an overview of the specific records used in DNS registration, check

http://www.petri.co.il/active_directory_srv_records.htm

Commented:
If it helps any: the client is not restricted to the domain controllers assigned to a specific site. If no domain controllers are assigned or available to a site, then the Infrastructure Master (specifically the Knowledge Consistency Checker, KCC) will assign a domain controller to a site. Otherwise, the client will prefer a domain controller in the same site.

Other than that, the sites in AD Sites & Services mainly define the replication topology.

Back in NT4, the security domains were also used as replication domains, and that didn't scale very well. The security domain remains, but the replication domain is now controlled by sites.
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