B.4 Services File

The sys:\etc\services file, as shown in Figure B-4, contains information about the known services used on the IP internetwork. Each entry provides information about one service. An entry cannot extend beyond one line.

Figure B-4 Sample Services File

The services file entry has the following format:

service_name port_number /protocol_name [alias [...]]

The service_name is the name of the service associated with this port number and protocol name. The name cannot contain a space, tab, pound sign (#), or end-of-line character. These are generally Application-layer, Presentation-layer, or Session-layer services, such as TFTP, FTP, SMTP, and TELNET.

The port_number is the number of the Internet port used by the service.

The protocol_name is the protocol with which the service is associated. This is generally a Transport-layer or Network-layer protocol, such as TCP or UDP. You must put a slash between the port number and the protocol name (for example, SMTP 25/TCP MAIL).

The alias is an alternate name for the service.

The sample file sys:\etc\samples\services is included with the TCP/IP software. When you are configuring TCP/IP for the first time, you should copy the sample services file from sys:\etc\samples to sys:\etc. You can then edit the sys:\etc\services file. You can change your configuration at any time by editing your existing sys:\etc\services file.