I have a rather puzzling problem with the LDAP access to Active Directory in a Windows domain. The configuration is as follows:
- There are two main networks: 192.168.0.0/24 and 192.168.100.0/24
- These networks are connected with an OpenVPN link (the transfer network is 192.168.201.0/30)
- A domain controller running Windows 2000 SP3 Server and Exchange 2000 in the 192.168.0.0/24 network
- Appropriate routing
- Both subnets registered with the site in the Sites and Services Snap-In
Almost everything works: users from the machines in both networks can log in, access SMB shares on file servers in the 192.168.0.0/24 network, use Outlook with their Exchange Account and so on. Also, all DNS queries, including the AD specific SRV records (e.g. _ldap._tcp.dc._msdcs.$DOMAINNAME), point to the correct places
There is no firewall on the OpenVPN link.
Now the problem: I cannot query the DC LDAP server (NTDS, port 389) from any computer in the 192.168.100.0/24 network. Interestingly, LDAP queries on the Global Catalog (port 3268 on the same server) work perfectly. I do even get a connection to port 389, but it gets reset immediately by the server.
There are no suspicious entries in the Directory Service Event Log (LDAP interface), even with the maximum possible log level.
Here the example output from LDP tool trying to connect to the DC at 192.168.0.1:
0x0 = ldap_unbind(ld); ld = ldap_open("192.168.0.1", 389); Established connection to 192.168.0.1. Retrieving base DSA information... Server error: <empty> Error<94>: ldap_parse_result failed: No result present in message Getting 0 entries:
Everything I found on the Web says the same two things, basically: "check the DNS" and "check the firewall". Well, I double- and triple-checked both the DNS and IP routing/filtering, and it seems to be fine.
Do you have any further ideas where to look and what to check? I'd appreciate any answer. If you need further diagnostic output, I'd be happy to provide it.
Thanks to adamo's answer, I've been able to narrow the problem further down. The problem is that all traffic to 192.168.0.0/24 network on port 389 somehow gets mangled by the machine OpenVPN is running on. This happens regardless of which target machine I am trying to connect to on port 389/tcp, and even regardless of whether the target machine is actually listening on port 389. Any other port (for example, 390) works fine, and I get either a connection or a "connection refused" message if no process is listening on that port.
Port 389/udp works fine, either.
What can cause a Windows 2000 server to mangle the traffic in this very selective way?
To minimize the interactions between the DC/NTDS services and the OpenVPN, I moved the OpenVPN server to another machine (and changed the IP routing accordingly). Now I am able to connect to any machine except the DC on the port 389/tcp. Nevertheless, if I try to connect to the LDAP server on the DC on port 389/tcp from the 192.168.100.0/24 network, the LDAP server closes the connection immediately, so basically I am back to square one.
Any ideas how to persuade the NTDS to talk to another network? Or maybe some workaround?