Augusto Alvarez

It’s a common best practice to run the DCDIAG tool in all DC in your forest whenever a significant change has been made, i.e. a new DC has been added or deleted in the forest. With this you are testing if the change you just made was done correctly.

It’s also common that if you have at least two domains in your forest (and the trust relationships in place), when you run dcdiag in any DC you get a message indicating that when the test of replication on a specific server applies, it fails indicating that the “RPC Server is unavailable”.

Well, if you see this message you probably check if that the RPC service is up and running on the server… running in cmd “net start rpcss”. But the command prompt answers you, “don’t worry dude, the service was already running”.

“Alright then…” you say, “Let’s try DCDIAG again”… and you get the same error like the first time…

And then you go like “Hmmmm… why do I keep getting the same “RPC Server is unavailable” error?”

And then I say “I know why dude!”… And then you “You do? Is there any way I can solve it?”…
“Of course, why I’ll be posting something that I don’t know the answer!”… and then…

OK, enough with the theatre…

This issue appears when the configurations between the different DNS servers are not compatible. It’s something like this: you have a correct configuration in a DNS server that forwards any requests that does not belong to his domain ; but in the second domain, the DNS server does not forward the requests that ask for the first domain… was it clear? Let’s do a picture then!

In this graphic, a contoso domain member it’s trying to get something from fabrikam, the DNS Server from contoso receive the request and see that it belongs to fabrikam and forwards the request to the correct DNS Server. But in the other side, a fabrikam user wants to get something from contoso but when it gets the requests, see that it’s not for fabrikam and it does not have anything that says that the request must be forward it to another DNS Server, so can’t solve the user’s request.

After naming “forward” several times you probably know where the problem is: The forwarders on your DNS servers are not set correctly. The most like problem is that having different domains in the same forest, the DNS servers from each domain don’t know were to direct the requests for all the other domains.

Let’s take one server to solve this problem: Access the DNS snap-in of your DNS Server, on “Properties” select the “Forwarders” option and select “New” in DNS Domain and add all the domains in your forest; and put the IP address to the DNS server holding that domain.

In this case, LEONARDO is DNS Server for CORPNET and I’m adding in the Forwarders configuration that any request for EXTRANET, my second domain in the forest, are been forwarded to its DNS Server. In EXTRANET the same configuration must be set, of course

Also there’s another way to solve this problem. You can add an EXTRANET zone in CORPNET Forward Lookup Zones that holds all of the DNS records for this domain. In this case you must also set, in EXTRANET DNS, the properties for this zone, to “Allow Zone Transfers”, letting another DNS server, CORPNET, to also have the records for this zone. But, in my opinion, is also a good idea to not over charge your DNS server with all kind of request, so if it’s not for his domain, forward to the correct DNS server for resolution.

If the error keeps appearing, then you should check the trust relationships between domains. And any other error message that DCDIAG shows in all DCs.

Cheers!

“My DC is online, the TCP/IP it´s OK, the DNS service running but I still cannot make a valid connection with AD! “

This is a problem that can be present in many ways. The most common example is: you have your DC completely configure for Active Directory, the DNS server too, and you try to join a workstation to your domain and the following error appears:

An Active Directory Domain Controller for the domain [yourdomain.com] could not be contacted.
Ensure that the domain name is typed correctly
(…)

First of all, the obvious: Check that the connectivity is working fine… the DNS server and the DC both of them responds to PING requests. It’s most likely that if you cannot connect to the domain, the PING requests for the FQDN (such as: ping dcname.yourdomain.com or ping yourdomain.com) will not respond as well… but with the IP parameter should be working… if it’s not, then there’s definitely a connectivity problem, a bad TCP/IP configuration or a firewall within the way .

Well, let’s see, this is a problem that can really make you nuts trying to solve it.

Let’s assume that you have the correct configuration in your DC and workstations. If you have a DHCP server in you network, check that he is doing his job… giving the correct IP address for the workstations, the subnet mask, the DNS server and the other parameters that you are using.

DCDIAG really? Can that help me?

One of the possible reasons of your problem is that DC didn’t register himself in the DNS for let the AD know that he is a valid domain controller. To do that, use the DCDIAG tool (included in the Windows 2003 Support Tools) as it follows:

dcdiag /test:registerindns /dnsdomain:yourdomain.com /v

Where yourdomain.com is the complete FQDN of your domain

If everything goes ok, you will get a message like this:

Using NSLOOKUP

NSLOOKUP is a very helpful utility to test the name resolution in a DNS server. You’ll use this tool to check the SRV (service) records are in place for the correct functionality of Active Directory.
Type in the command line nslookup and press enter. You will probably find a message like this:

“*** Can’t find name server for the address : Non-existent domain”, don’t worry about it. This happens when you don’t have set any PTR (or reverse records) in your DNS server, to resolve IP address in names.

Carry on then, at nslookup (”>”) prompt type:

set q=srv press enter.

Then type: _ldap._tcp.dc._msdcs.yourdomain.com

Again, sometimes because you don’t have any PTR records you may find some “time out” messages, but there is nothing vital at this point.

If there is no problem with that, you will see the DNS server name and its IP address… if you don’t, you still have one thing to do.

That thing you never wanted to do… modifying a .dns file

The file that probably will save you is saved in: C:\WINDOWS\system32\config and with the name netlogon.dns.

You have to open this file with the notepad and take a look to it, but don’t get frightened! … You will see a bunch of lines that will probably don’t have much sense to you, but one of them we are looking for:

_ldap._tcp.yourdomain.com IN SRV 0 0 389 ldap_server_name
_ldap._tcp.dc._msdcs.yourdomain.com IN SRV 0 0 389 domain_controller_name

The LDAP server name should be the same for the DC server name. So if you are going to manually change this file, use them as the same.

I’m gonna publish some other documents for similar problems. They all are from situations like you lost your only DC and you get back on service an old backup that has a different configuration. Check them too.

Cheers everyone!