internet dns name resolution

my server is a domain controller for my private network and i am giving internet for my clients through nat. my clients are connecting to internet and browsing but they can’t browse through server directly, i got why

1. the name resolution traffic is not directly external source, the dns name given at my client is my server ip. if i give dns ip of isp then my clients are resolving names. At my server is configured as nat and ip addresses allocation is automatic(dhcp).
can any one help me in this regard.