Microsoft KB Archive/136403

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Article ID: 136403

Article Last Modified on 12/5/2003


  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Server 3.5
  • Microsoft Windows NT Server 3.51
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Workstation 3.5
  • Microsoft Windows NT Workstation 3.51
  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft TCP/IP for Windows for Workgroups 3.11
  • Microsoft TCP/IP for Windows for Workgroups 3.11a
  • Microsoft TCP/IP for Windows for Workgroups 3.11b

This article was previously published under Q136403


The User Datagram Protocol is an unreliable, connectionless oriented protocol that uses an IP address for the destination host and a port number to identify the destination application.

The UDP port number is distinct from any physical port on a computer such as a COM port or an I/O port address. The UDP port is a 16-bit address that exists only for the purpose of passing certain types of datagram information to the correct location above the transport layer of the protocol stack.


UDP ports are not the same as TCP ports, though TCP and UDP may use the same port number in certain instances. The UDP ports can receive more than one message at a time, and they are identified by "well known" port numbers. The following is a listing of some of the more common "well known" UDP ports:

Port   Keyword       Description
----   -----------   ------------------------------

15     NETSTAT       What is the network status

53     DOMAIN        Domain Name Server

69     TFTP          Trivial File Transfer Protocol

137    NETBIOS-NS    NetBIOS name service

138    NETBIOS-DGM   NetBIOS datagram service

161    SNMP          SNMP network monitor

The UDP specification is defined in RFC 768.

Note: The NETBIOS-NS (NetBIOS name service) port value can be configured to accommodate products from specific vendors. The Registry parameter that controls this value is NameServerPort.

For additional information on the NameServerPort parameter, please see the following article(s) in the Microsoft Knowledge Base:

120642 TCP/IP and NBT Configuration Parameters for Windows 2000 or Windows NT


"Inter-Networking with Microsoft TCP/IP Using Microsoft Windows NT, Participant's Workbook," P/N 4275A, Appendix A, page 222.

"TCP/IP Illustrated, Volume 1, The Protocols," W. Richard Stevens, pp 6,7,12,13, Addison-Wesley, 1994.

Additional query words: ppp endpoint connection

Keywords: KB136403