外部DNS可以的,但是需要能够支持动态更新和SRV记录。
WINDOWS AD就可以正常使用了,并不要求使用WINDOWS作为DNS服务器。
参考这里,
DNS Domain Name Registration
Active Directory supports dynamic registration of domain controller addresses in DNS. After Active Directory has been installed during domain controller creation, the Net Logon service dynamically creates records in the DNS database that are used to locate the server. Dynamic update (described in RFC 2136) is a recent addition to the DNS standard; this addition to the standard defines a protocol for dynamically updating a DNS server with new or changed resource record values. Before the advent of this new protocol, administrators had to manually create the records that are stored on DNS servers. The implementation of DNS server that is included with Windows Server 2003 and later supports dynamic updates, as does the Berkeley Internet Name Domain (BIND) version 8.x implementation of DNS.
https://technet.microsoft.com/en-us/library/cc759550(v=ws.10).aspx