Xpeed 320R, Руководство пользователя

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IP Networking Basics Network Address Translation
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subnets to individual departments or floors, dividing the network logically into
easily manageable groups.
ISPs also use subnets to assign a range of IP addresses for a business customer. A
Class C network with 256 addresses can be divided into 32 subnets each with 8
host addresses. (Note that two of those addresses can not be used; please see the
section on IP Addressing.) This allows the ISP to effectively support 32 small
businesses with multiple IP addresses.
The subnet used in this example is as follows:
11111111.11111111.11111111.11111000 (255.255.255.248)
The last three bits are left blank, allowing for 8 host IP addresses.
Typically, all hosts on a LAN segment will use the same subnet. This allows all
the hosts to recognize local IP broadcasts, and allows the router to differentiate
between local and remote addresses.
5. N
ETWORK
A
DDRESS
T
RANSLATION
Typically, you will deal with two sets of IP addresses. One or more IP addresses
will be assigned to you by your ISP. This will be referred to as the WAN IP
address. Another set of IP addresses will be used in your LAN; each host on your
LAN will have its own IP address. The LAN and WAN IP addresses are indepen-
dent of each other, if you are using a feature called Network Address Translation
(NAT) which allows you to map LAN addresses to the WAN. A key benefit of
NAT is the ability to map multiple LAN addresses to a single WAN IP address, a
feature commonly known as line-sharing.
Traditionally, the way that ISPs supported line-sharing was to assign a block of IP
addresses. However, NAT allows multiple users to share a single IP address,
which may be assigned statically or dynamically by the ISP.
NAT works by translating the internal IP addresses to a single global address as
illustrated below.