ZyXEL Communications VSG-1200 V2, User Manual

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VSG-1200 V2 User’s Guide
61 Chapter 6 LAN and WAN Setup
The Internet Assigned Number Authority (IANA) reserved a block of addresses specifically
for private use (refer to
Section 6.3.2 on page 61 ); please do not use any other number unless
you are told otherwise. Let’s say you select 192.168.1.0 as the network number; which covers
254 individual addresses, from 192.168.1.1 to 192.168.1.254 (zero and 255 are reserved). In
other words, the first three numbers specify the network number while the last number
identifies an individual computer on that network.
The subnet mask specifies the network number portion of an IP address.
6.3.2 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.
Regardless of your particular situation, do not create an arbitrary IP address; always follow the
guidelines above.
Note: 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.
6.3.3 DNS Server Address
DNS (Domain Name System) is for mapping a domain name to its corresponding IP address
and vice versa, for example, the IP address of
www.zyxel.com is 204.217.0.2. The DNS server
is extremely important because without it, you must know the IP address of a machine before
you can access it. The DNS server addresses that you enter in the DHCP setup are passed to
the client machines along with the assigned IP address and subnet mask.
There are two ways that an ISP disseminates the DNS server addresses. The first is for an ISP
to tell a customer the DNS server addresses, usually in the form of an information sheet, when
s/he signs up. The second is to obtain the DNS server information automatically when a
computer is set as a DHCP client.