Messages

Configuring Priority on a DC:
Configure the LdapSrvPriority registry setting on your domain controllers so that DC3 has the highest priority. For more info about this setting, see here:

http://technet.microsoft.com/library/cc957290

In addition you can configure the LdapSrvWeight registry setting on domain controllers to assign a weighted priority for each one:

http://technet.microsoft.com/en-us/library/cc957291

Of course, this will mean that all client computers (not just SNOOPY) will prefer DC3 for logons, and it doesn't actually guarantee DC3 will be used because if DC3 is unavailable then domain controllers with lower weighted priority will be tried in order.

From this site:  http://serverfault.com/questions/318707/force-windows-server-to-use-specific-domain-controller
"Configuring sites is of course a good start. However you should still be aware that you cannot "force" the usage of a specific DC using Sites and Services. This is by design. For example, if the DC in your site is down, Windows should try a DC in another site.

If you have a topology with a main location (such as HQ or datacenter) and remote "spoke" sites with DC's that only need to perform local authentication and other DC functions, the remote DC's can be configured to not advertise certain services by using the DnsAvoidRegisterRecords registry setting.

Also note that you can influence preference order by using the Priority and Weight of the SRV DNS records in the _msdcs subdomain, but that should only be done after a thorough analysis. Clients attempt to contact the server with the lowest priority. Weight is a load-balancing mechanism that is used when selecting a target host from those that have the same priority. Clients randomly choose SRV records that specify target hosts to be contacted, with probability proportional to the weight."

More information:

How to optimize the location of a domain controller or global catalog that resides outside of a client's site
http://support.microsoft.com/kb/306602

SRV Resource Records
http://technet.microsoft.com/en-us/library/cc961719.aspx