Prevent DNS access

This article discusses the steps for preventing users from accessing the DNS server.

1. To prevent DNS server jobs from starting automatically when you start TCP/IP, type the following: CHGDNSA AUTOSTART(*NO)

   AUTOSTART(*NO) is the default value.

2. To prevent someone from associating a user application, such as a socket application, with the port that the system normally uses for DNS, do the following:
   1. Type GO CFGTCP to display the Configure TCP/IP menu.
   2. Select option 4 (Work with TCP/IP port restrictions).
   3. On the Work with TCP/IP Port Restrictions display, specify option 1 (Add).
   4. For the lower port range, specify 53.
   5. For the upper port range, specify *ONLY.
      Note: The port restriction takes effect the next time that you start TCP/IP. If TCP/IP is active when you set the port restrictions, you should end TCP/IP and start it again.
   6. For the protocol, specify *TCP.
   7. For the user profile field, specify a user profile name that is protected on your system. (A protected user profile is a user profile that does not own programs that adopt authority and does not have a password that is known by other users.) By restricting the port to a specific user, you automatically exclude all other users.
   8. Repeat steps 2c through 2g for the *UDP (user datagram) protocol.