3Com 4200G PWR Getting Started Manual page 58

58 C 4: P S
HAPTER ROBLEM OLVING
If your IP network is internal to your organization only, that is, you do not
access the Internet, you may use any arbitrary IP address as long as it is
not being used by another device on your network. 3Com suggests you
use addresses in the range 192.168.0.0 to 192.168.255.255 with a
subnet mask of 255.255.255.0.
These suggested IP addresses are part of a group of IP addresses that
have been set aside specially for use 'in house' only.