In DNS,it works with both TCP n UDP.so when it uses UDP and when it uses TCP protocol?

See The TCP/IP Guide - DNS Message Generation and Transport (http://www.tcpipguide.com/free/t_DNSMessageGenerationandTransport-2.htm) for a general overview and RFC 1035 (http://www.ietf.org/rfc/rfc1035.txt) for more details. Given that the RFCs are the "specification", I would also expect differences between any two individual DNS implementations.

I second Scleros. Unix type DNS implementation is different than Windows DNS and specifically, Active Directory Integrated DNS which is saved in the registry and replicates based on Active Directory synchronization schedules.

There are also distinct differences between server based DNS and the DNS client.