I'm running into some connectivity problems with my two Domain Controllers (DC). I have one primary DC and one backup DC, both set up on different networks with two Network Interface Cards (NICs). While Active Directory and DNS seem to replicate without issues and pass all the necessary diagnostics tests, I'm facing a couple of major headaches:
1. Nslookup on the backup DC (dc2) fails, but it works fine for the primary DC (dc1).
2. Sometimes, dc2 isn't reachable via ping, even though it usually is.
3. Linux machines occasionally fail to join the domain, and there are times where they can't log in with their domain accounts.
It seems like a DNS issue is at play here, but I'm not certain how to fix it. Currently, dc1 is set to use 127.0.0.1 as its primary DNS and dc2 as its secondary. Conversely, dc2 has dc1 as its primary and itself as secondary. Additionally, there's a second network with DNS configured on the NICs, which I'm worried might contribute to the problem.
3 Answers
Definitely give those DNS settings a try. Remember, you should have each DC point to the other as the primary, and its own loopback address as secondary. And about having two NICs, it's generally not recommended for DCs to be dual-homed unless you have a specific setup that requires it.
It sounds like your DNS configuration is off. You want DC1 to have DC2 as its primary DNS and 127.0.0.1 as the secondary. Meanwhile, DC2 should be set to have DC1 as its primary DNS and 127.0.0.1 as the secondary. Just make sure all your clients are directed towards these two DCs for DNS resolution. Also, for your second network, it seems like it might be causing conflicts since DCs shouldn't be dual-homed like that.
Don't forget, your DNS should only include the DCs. If you have additional DNS lookups, consider using forwarders or root hints to improve the situation. Keeping your DCs isolated from other networks could help as well.
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