Linux Know-How provides a collection of introductory texts on often needed Linux skills.

The /Etc/Services File

This is where it all begins. When a client connects to the firewall it connects on a known port (less then 1024). For example telnet connects on port 23. The inetd deamon hears this connection and looks up the name of these service in the /etc/services file. It then calls the program assigned to the name in the /etc/inetd.conf file.

Some of the services we are creating are not normally in the /etc/services file. You can assign some of them to any port you want. For example, I have assigned the administrator's telnet port (telnet-a) to port 24. You could assign it to port 2323 if you wished. For the administrator (YOU) to connect directly to the firewall you will need to telnet to port 24 not 23 and if you setup your netperm-table file, like I did, you will only be able to this from one system inside your protected network.

  telnet-a        24/tcp
  ftp-gw          21/tcp           # this named changed
  auth            113/tcp   ident    # User Verification
  ssl-gw          443/tcp

Last Update: 2010-12-16