ZyXEL NBG-318S Guia Do Utilizador

Appendix C IP Addresses and Subnetting

NBG-318S User’s Guide

Where you obtain your network number depends on your particular situation. If the ISP or 
your network administrator assigns you a block of registered IP addresses, follow their 
instructions in selecting the IP addresses and the subnet mask.
If the ISP did not explicitly give you an IP network number, then most likely you have a single 
user account and the ISP will assign you a dynamic IP address when the connection is 
established. If this is the case, it is recommended that you select a network number from 
192.168.0.0 to 192.168.255.0. The Internet Assigned Number Authority (IANA) reserved this 
block of addresses specifically for private use; please do not use any other number unless you 
are told otherwise. You must also enable Network Address Translation (NAT) on the NBG-
318S. 
Once you have decided on the network number, pick an IP address for your NBG-318S that is 
easy to remember (for instance, 192.168.1.1) but make sure that no other device on your 
network is using that IP address.
The subnet mask specifies the network number portion of an IP address. Your NBG-318S 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 NBG-318S unless you are instructed to do 
otherwise.

Every machine on the Internet must have a unique address. If your networks are isolated from 
the Internet (running only between two branch offices, for example) 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.
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.

14

255.255.255.252 (/30)

16384

2

15

255.255.255.254 (/31)

32768

1

Table 108   16-bit Network Number Subnet Planning (continued)