Windows 2000 Well Known Ports

This list is not intended to be a comprehensive listing of standard ports, but does include those that are most pertinent to Windows 2000 and other MS operating systems.

If you want to see which ports are in use on your PC, then from command prompt use "netstat -an" this should display all connections and listening ports in numerical form.

If you find that your machine is using a port that you didn't expect and want to find out which application is accessing that port, then the only easy way I have found is to download tcpview from Sysinternals (it's on both the Links and Downloads pages above).

21/TCP (Transmission Control Protocol) -- FTP
This File Transfer Protocol (FTP) server is part of Internet Information Services (IIS) and is administered from the IIS administration tool. FTP is a common method to transfer files between two networked computers and to enable the convenient use of remote file storage capabilities.

25/TCP -- SMTP
This Simple Mail Transfer Protocol (SMTP) service is administered from the IIS administration tool. SMTP is the protocol that is used to send e-mail messages by means of the Internet.

53/TCP -- DNS
Domain Name System (DNS) enables you to use hierarchical, friendly names to easily locate computers and other resources on an IP network. The resolution of names through the use of Domain Name System (DNS) is central to Windows 2000 operation. Without correct name resolution, users cannot locate resources on the network.

80/TCP -- HTTP
Hypertext Transfer Protocol (HTTP) is the set of rules for exchanging files (for example, text, graphic images, sound, video, and other multimedia files) on the World Wide Web (WWW). In comparison to the TCP/IP suite of protocols (that are the basis for information exchange on the Internet), HTTP is a program protocol.

88/UDP (User Datagram Protocol) -- Kerberos
Kerberos protocol is a network authentication method that is based on the key distribution model. This protocol enables entities that are communicating over networks to prove their identity to each other and at the same time this protocol can prevent eavesdropping or replay attacks. The Kerberos Key Distribution Center (KDC) listens on this port for ticket requests. Port 88 for the Kerberos protocol can also be TCP/UDP.

119/TCP -- NNTP
Network News Transfer Protocol (NNTP) is the predominant protocol that is used by computers for managing the notes that are posted on Usenet newsgroups. NNTP servers manage the global network of collected Usenet newsgroups.

135/TCP -- RPC
Remote procedure call (RPC) is a facility that enables a program on one Windows-based computer (the client computer) to invoke the services of another program that is running on a separate Windows-based computer (the server) in a distributed network. RPC is a program-level protocol that can use the communications services of any of the Windows networking protocols, which includes TCP/IP.

137/UDP -- NetBIOS Name Server
The network basic input/output system (NetBIOS) Name Server (NBNS) protocol, which is part of the NetBIOS over TCP/IP (NetBT) family of protocols, provides a means for hostname and address mapping on a NetBIOS-aware network.

138/UDP -- NetBIOS Datagram
The NetBIOS Datagram is part of the NetBIOS over TCP/IP (NetBT) family of protocols and is used for network logon and browsing.

139/TCP -- NetBIOS Session Services
NetBIOS Session Services are part of the NetBIOS over TCP/IP (NetBT) family of protocols and is used for server message block (SMB), file sharing, and printing.

389/UDP -- LDAP
LDAP is the Lightweight Directory Access Protocol. LDAP is designed to be a standard way of providing access to directory services. In Windows 2000, LDAP is the primary way that the operating system accesses the Active Directory database.

443/TCP -- HTTPS
Secure Hypertext Transfer Protocol (HTTPS) is a variant of HTTP that is used for handling secure transactions. HTTPS is a unique protocol that is Secure Sockets Layer (SSL) under HTTP.

445/TCP -- SMB
The SMB protocol is used for file sharing in Microsoft Windows NT and Windows 2000. Windows 2000 enables you to run SMB directly over TCP/IP, without the extra layer of NetBT.

464/TCP -- Kerberos Password V5
The Kerberos change password protocol is used to deny an administrator from setting a password for a new user. This functionality is useful in some environments, and this proposal can be used to enable password setting. This protocol is used when users changes their passwords.

500/TCP -- ISAKMP
Internet Security Association and Key Management Protocol (ISAKMP) or IKE (for Windows 2000) is the key exchange mechanism for a virtual private network (VPN). ISAKMP manages the exchange of cryptographic keys and uses a two-phase process for establishing the Internet Protocol security (IPSec) connection between two gateways.

563/TCP -- SNEWS
SNEWS is secure NNTP.

593/TCP -- RPC over HTTP
RPC over HTTP is used for COM+ Internet Services and requires IIS to operate.

636/TCP -- LDAP over SSL
When SSL is enabled, LDAP data that is transmitted and received is encrypted.

1067/TCP -- Installation Bootstrap Service
The installation bootstrap protocol server.

1068/TCP -- Installation Bootstrap Service
The installation bootstrap protocol client.

1645/UDP -- IAS: Internet Authentication Service
This service is used for processing Remote Authentication Dial-In User Service (RADIUS) authentication messages and is supported by IAS to provide backward compatibility with earlier RADIUS servers.

1646/UDP -- IAS: Internet Authentication Service
This service is used for processing RADIUS accounting messages and is supported by IAS to provide backward compatibility with earlier RADIUS servers.

1701/UDP -- L2TP
Layer 2 Tunneling Protocol (L2TP) is a method for encapsulating standard Point-to-Point Protocol (PPP) by means of a variety of media. The protocol also enables encapsulation of PPP by using UDP packets.

1723/UDP -- PPTP
PPTP is an abbreviation for Point-to-Point Tunneling Protocol. It is an Internet protocol that is frequently used in VPN products. Windows NT supports PPTP server, and both Windows NT and Microsoft Windows 95 support PPTP client.

1812/UDP -- IAS Internet Authentication Service
This service is used for processing RADIUS authentication messages.

1813/UDP -- IAS Internet Authentication Service
This service is used for processing RADIUS authentication messages.

3268/TCP -- Microsoft Global Catalog
Active Directory global catalogs listen on this port.

3269/TCP -- Microsoft Global Catalog with LDAP/SSL
Microsoft global catalog SSL connections listen on this port.

3389/TCP -- RDP
Remote Desktop Protocol (RDP) is the protocol that enables a thin client to communicate with the Terminal server over the network. This protocol is based on the International Telecommunication Union (ITU) T.120 protocol, an international, standard multiple-channel conferencing protocol that is currently being used in the Microsoft NetMeeting conferencing software product.