5.3.3. Edit the /var/yp/securenets File

NIS listens to all networks, if the /var/yp/securenets file is blank or does not exist (as is the case after a default installation). One of the first things to do is to put netmask/network pairs in the file so that ypserv only responds to requests from the proper network.
Below is a sample entry from a /var/yp/securenets file:
 255.255.255.0 192.168.0.0 

Warning

Never start an NIS server for the first time without creating the /var/yp/securenets file.
This technique does not provide protection from an IP spoofing attack, but it does at least place limits on what networks the NIS server services.