Internal sites are not reachable on F5 explicit forward proxy.

Hello Guys,

 

We have a explicit F5 forward proxy server where I am able to access all external sites and it works fine however I can't reach any my internal sites , It said "DNS lookup failed " .

 

from Big IP I can resolve these sites but not working in browser., In DNS resolver list I have called the internal DNS server which can resolve all the DNS entries internal and external.

 

So please suggest where I need to work to fix this issue .