ZyXEL Communications P-791R, User Manual

Page: 316 / 358

Appendix D IP Addresses and Subnetting
P-791R v2 User’s Guide
316
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 ZyXEL
Device.
Once you have decided on the network number, pick an IP address for your ZyXEL Device
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 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 (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 110 16-bit Network Number Subnet Planning (continued)
NO. “BORROWED”
HOST BITS
SUBNET MASK NO. SUBNETS
NO. HOSTS PER
SUBNET