DNS Refuses to Resolve

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rkymtnhigh
Posts: 3
Joined: 2016/02/26 18:21:56

DNS Refuses to Resolve

Post by rkymtnhigh » 2017/07/10 20:32:54

I started building a new environment at AWS not long ago, but was pulled away for other projects. Now I've been asked to start work at AWS again, and I've run into an immediate snag.

I had a Windows Active Directory domain set up, that the Centos box talked to just fine. 2 Windows Server 2008r2 domain controllers.
After turning everything back on, CentOS refused to resolve any DNS queries, saying it could not contact the DNS server. I was having some issues with one of the DC's, so I decided to try removing the domain from the equation- pointing CentOS at 8.8.8.8 for DNS. So I've set my DNS server to 8.8.8.8 and am able to ping/telnet to that address. However, nslookup, dig, ping by DNS name, all fail, saying DNS server cannot be reached. I've made sure iptables is stopped, but I don't think that's the issue because I am able to telnet to 8.8.8.8 over TCP port 53.

I am not having much luck troubleshooting this issue. Any help or pointers are greatly appreciated!

Thanks!

RMH

aks
Posts: 3073
Joined: 2014/09/20 11:22:14

Re: DNS Refuses to Resolve

Post by aks » 2017/07/11 15:54:19

FYI DNS uses UDP and only fails over to TCP for large amount of information (so your test is invalid).

rkymtnhigh
Posts: 3
Joined: 2016/02/26 18:21:56

Re: DNS Refuses to Resolve

Post by rkymtnhigh » 2017/07/11 17:04:16

aks, thank you! That was our issue, UDP ports got locked down

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