If you are considering giving your Active Directory name just a single level name, don't do it. Just stop and pick a new name. If your already stuck with a single level AD domain, I feel your pain. I see the warning now when I try to fix my problems after the fact.
So whats the big deal? Windows XP and Server 2003 do not update DNS records to a single level domain. They also have issues joining a domain cross subnet. Our biggest problems show up when dealing with more then one subnet.
The main problem is that DNS will be missing records. Domain controllers have lots of integration with DNS. So if one of those is not updating its DNS records, you have a huge mess. Domain controllers failing to replicate was our big issue. Every time we added a domain controller, we ended up rebuilding the DNS records by hand. Adding the new server keys where needed. Most of the time replication would work one way but not the other. Fixing DNS fixed replication.
Over time I have uncovered more documentation and most importantly this registry key:
I run this on every server just to make sure. Once you run this, you will have to reboot the server so the netlogon process can register the DNS.
You can run this on your workstations if you want them in your DNS too. we opted not to for most of ours.
I believe there is now a group policy setting that sets the same value. But I do not recall where it is. If I find it, I will update this post.
The second big issue we ran into was we could not join the domain from the other subnets. In XP and 2003, Microsoft changed them to use DNS more. The computer could see the domain and tell you that it exists. It would even point out that the SRV records in DNS are correct. But it would fail to join. At some point in the process it sees the single level domain name and used netbios instead of DNS. It would work fine if on the same subnet, but with out a wins server or lmhost file it would fail.
For the longest time, we used a lmhost file to point to the domain. We built it into the default ghost image and it worked great. Then came the network restructure that ended up changing our IP range. Evey one of those file we used in the last several years had to be updated. The symptom was a 10 min login on those computers for existing users on the computer.
Here is a sample of what we put in the lmhost file
10.0.0.1 servername1 #PRE #DOM:doaminname
10.0.0.2 servername2 #PRE #DOM:domainname
10.0.0.1 "domainname \0x1b" #PRE
10.0.0.2 "domainname \0x1b" #PRE
Inside the quotes on the bottom line must be exactly 20 characters or it won't work.After saving the changes to the LMHOSTS file you have to enable NetBIOS over TCP/IP and import theLMHOSTS file.
The correct way to do this would be to set up a wins server. One experiment that I tried was to put one of the domain controllers address as the wins server and it solved our import issue. The only thing we needed a wins server for was to join computers to the domain on a different subnet. By telling the computer that the domain controller is the wins server, it was able to find it and import just fine.
So our work around was to run a registry hack on every server so they update DNS and to put in a fake wins server address that points to our domain controller for workstation importing.