I have a complex customer environment where Microsoft Identity Manager is managing identities across three Active Directory Forests. The Forests all serve different purposes and are contained in different network zones. Accordingly there are firewalls between the zone where the MIM Sync Server is located and two of the other AD Forests as shown in the graphic below.
As part of the project the maintainers of the network infrastructure had implemented rules to allow the MIM Sync server to connect to the other two AD Forests. I had successfully been able to create the Active Directory Management Agents for each of the Forests and perform synchronization imports.
The Error ‘kerberos-no-logon-server’
Everything was going well right up to the point I went to export changes to the two AD Forests that were separated by firewalls. I received the ‘kerberos-no-logon-server’ error as shown below from the run profile output.
I started investigating the error as I hadn’t encountered this one before. There were a few posts on the possibilities mainly dealing with properties of the AD MA’s configuration. But I did stumble on a mention of kerberos being used when provisioning users to Active Directory and setting the initial password. That aligned with what I was doing. I had provided the networking engineers with my firewall port requirements. Those are (no PCNS required for this implementation) ;
- 389 TCP – LDAP
- 636 TCP – LDAPS
- 88 TCP – Kerberos
- 464 TCP/UDP – Kerberos
- 53 TCP – DNS
- 3268 TCP/UDP – Global Catalog
- 3269 TCP/UDP – Global Catalog
- 135 TCP – RPC
My old school immediate thought was to Telnet to each of the ports to see if the firewall was allowing me through. But with a couple of forests to test against and UDP ports as well, it wasn’t going to be that easy. I found a nice little Test-Port function that did both TCP and UDP. I already had an older script for testing TCP ports via PowerShell. So I combined them.
Identifying the cause
As suspected connectivity to the forest where my MIM Sync Server was located was all good. The other two, not so much. GC connectivity wouldn’t give me the Kerberos error, but not having Kerberos Port 464 certainly would.
In the backwards and forwards with the networking team I had to test connectivity many times so I added a running output as well as a summary output. The running output highlighting ports that weren’t accessible.
Here’s the raw script if you’re in a similar situation. Get the Test-Port Function from the URL in line 1 to test UDP Port connectivity. Add additional ports to the arrays if required (eg. for PCNS), and update the forest names in lines 21-23.
I’m sure this is going to become more relevant in a Cloud/Hybrid world where MIM Servers will be in Azure, Active Directory Forests will be in different networks and separated by firewalls and Network Security Groups.