ISE Issue with DNS

Question

Hello Techies,
I am facing challenge while configuring ISE to join AD. Domain Name lookup fails. DNS is working perfectly fine;
nslookup works fine on ISE for simple domain names, but on long domain  names it fails while throwing the following error;
;; Truncated, retrying in TCP mode.
;; connection timed out; no servers could be reached
Upon searching on google, may threads discuss that it a common issue with linux, when multiple IP's are returned for DNS query. Solution is to make static entries in;
/etc/resolv.conf
Not able to find it in ISE, as it does not give access to the OS. I am running it on VMware.
Looking forward to get your valuable inputs to resolve this.
Thanks

Answer 1

Thanks for your response. Port 53(TCP) was opened on firewall & voila........nslookup was able to resolve the hostname.
Now there is another challenge because of huge environment. Active Directory forest contains  more than 50+ child domain controllers. Policy is open for one particular hostname/ip. But authentication is not successful & ISE is not able to join domain. CISCO forums says that ports for all server should be open for ISE on the intermediate firewall, but it is a huge challenge for testing.
While I tried to give the FQDN of specific server(from whom ports are open on firewall), it is not getting resolved again.
Please sugeest