Monday, October 7, 2002 03:41 PM
The DNS assumes that messages will be transmitted as datagrams or in a
byte stream carried by a virtual circuit. While virtual circuits can be
used for any DNS activity, datagrams are preferred for queries due to
their lower overhead and better performance. Zone refresh activities
must use virtual circuits because of the need for reliable transfer.
The Internet supports name server access using TCP [RFC-793] on server
port 53 (decimal) as well as datagram access using UDP [RFC-768] on UDP
port 53 (decimal).
Seems like it is possible some name servers support UDP only and some also TCP. You may want to try opening a DatagramSocket so that your query uses UDP instead.