ZyXEL Communications NWA 1121-NI -, User Manual

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Appendix C IP Addresses and Subnetting
NWA1121-NI User’s Guide
178
Configuring IP Addresses
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 NWA1121-NI.
Once you have decided on the network number, pick an IP address for your NWA1121-NI 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 NWA1121-NI 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 NWA1121-NI 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 (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.
13 255.255.255.248 (/29) 8192 6
14 255.255.255.252 (/30) 16384 2
15 255.255.255.254 (/31) 32768 1
Table 51
16-bit Network Number Subnet Planning (continued)
NO. “BORROWED”
HOST BITS
SUBNET MASK NO. SUBNETS
NO. HOSTS PER
SUBNET