External and Internal DNS on same appliance

Thank you for your suggestions I appreciate it. My concern was to not provide internal IP address to the external users. Now I see that there is no reason to create new listener because when I want to protect the records I need to do it with iRule on WideIP as per Paulius solution for Split DNS, and as I do not need Split DNS I am using simpler iRule to allow DNS response only to private IP addresses. And for the discussion how to organize this internal only records and still use GSLB is your solution zamroni777 very nice and we will consider it, in our case we can create cname records on internal DNS servers and no records on external servers, and to combine this 2 solutions for better protection apply also iRule on the internal only WideIPs on F5.