Internet services and port numbers

The TCP/IP protocol suite is the lingua franca of the Internet because the Internet services “speak” TCP/IP. These services make the Internet tick by making possible the transfer of mail, news, and Web pages. Each Internet service has its own protocol that relies on TCP/IP for the actual transfer of the information. Each service also has one or more assigned port numbers
that it uses to do whatever it’s designed to do. Here are some well-known Internet services and their associated protocols:

1. DHCP (Dynamic Host Configuration Protocol) is for dynamically configuring TCP/IP network parameters on a computer. DHCP is primarily used to assign dynamic IP addresses and other networking information such as name server, default gateway, domain names that are needed to configure TCP/IP networks. The DHCP server listens on port 67.
2. FTP (File Transfer Protocol) is used to transfer files between computers on the Internet. FTP uses two ports — data is transferred on port 20; control information is exchanged on port 21.
3. HTTP (HyperText Transfer Protocol) is for sending documents from one system to another. HTTP is the underlying protocol of the Web. By default, the Web server and client communicate on port 80.
4. SMTP (Simple Mail Transfer Protocol) is for exchanging e-mail messages between systems. SMTP uses port 25 for information exchange.
5. NNTP (Network News Transfer Protocol) is for distribution of news articles in a store-and-forward fashion across the Internet. NNTP uses port 119.
6. SSH (Secure Shell) is a protocol for secure remote login and other secure network services over an insecure network. SSH uses port 22.
7. TELNET enables a user on one system to log in to another system on the Internet (the user must provide a valid user ID and password to log in to the remote system).
   
8. TELNET uses port 23 by default. However, the TELNET client can connect to any specified port.
9. NFS (Network File System) is for sharing files among computers. NFS uses Sun’s Remote Procedure Call (RPC) facility, which exchanges information through port 111.
10. NTP (Network Time Protocol) is used by client computers to synchronize the system time with that on a server (one with a more accurate clock). NTP uses port 123.
11. SNMP (Simple Network Management Protocol) is for managing all types of network devices on the Internet. Like FTP, SNMP uses two ports: 161 and 162.
12. TFTP (Trivial File Transfer Protocol) is for transferring files from one system to another (typically used by X terminals and diskless workstations to download boot files from another host on the network). TFTP data transfer takes place on port 69.

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