ZyXEL Communications P-660HN-51 User Manual page 108

The subnet mask specifies the network number portion of an IP address. Your Zyxel Device will compute
the subnet mask automatically based on the IP address that you entered. You don't need to change
the subnet mask computed by the Zyxel Device unless you are instructed to do otherwise.
Private IP Addresses
Every machine on the Internet must have a unique address. If your networks are isolated from the
Internet, for example, only between your two branch offices, you can assign any IP addresses to the
hosts without problems. However, the Internet Assigned Numbers Authority (IANA) has reserved the
following three blocks of IP addresses specifically for private networks:
• 10.0.0.0 — 10.255.255.255
• 172.16.0.0 — 172.31.255.255
• 192.168.0.0 — 192.168.255.255
You can obtain your IP address from the IANA, from an ISP or it can be assigned from a private network.
If you belong to a small organization and your Internet access is through an ISP, the ISP can provide you
with the Internet addresses for your local networks. On the other hand, if you are part of a much larger
organization, you should consult your network administrator for the appropriate IP addresses.
Note: Regardless of your particular situation, do not create an arbitrary IP address; always
follow the guidelines above. For more information on address assignment, please refer
to RFC 1597, "Address Allocation for Private Internets" and RFC 1466, "Guidelines for
Management of IP Address Space".
Chapter 7 Home Networking
P-660HN-51 User's Guide
108