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The following table is a summary for subnet planning on a network with a 16-bit
network number.
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
Table 89
16-bit Network Number Subnet Planning
NO. “BORROWED”
HOST BITS
SUBNET MASK
NO.
SUBNETS
NO. HOSTS PER
SUBNET
1
255.255.128.0 (/17)
2
32766
2
255.255.192.0 (/18)
4
16382
3
255.255.224.0 (/19)
8
8190
4
255.255.240.0 (/20)
16
4094
5
255.255.248.0 (/21)
32
2046
6
255.255.252.0 (/22)
64
1022
7
255.255.254.0 (/23)
128
510
8
255.255.255.0 (/24)
256
254
9
255.255.255.128 (/25)
512
126
10
255.255.255.192 (/26)
1024
62
11
255.255.255.224 (/27)
2048
30
12
255.255.255.240 (/28)
4096
14
13
255.255.255.248 (/29)
8192
6
14
255.255.255.252 (/30)
16384
2
15
255.255.255.254 (/31)
32768
1
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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.
IP Address Conflicts
Each device on a network must have a unique IP address. Devices with duplicate
IP addresses on the same network will not be able to access the Internet or other
resources. The devices may also be unreachable through the network.
Conflicting Computer IP Addresses Example
More than one device can not use the same IP address. In the following example
computer
A
has a static (or fixed) IP address that is the same as the IP address
that a DHCP server assigns to computer
B
which is a DHCP client. Neither can
access the Internet. This problem can be solved by assigning a different static IP
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address to computer
A
or setting computer
A
to obtain an IP address
automatically.
Figure 157
Conflicting Computer IP Addresses Example
Conflicting Router IP Addresses Example
Since a router connects different networks, it must have interfaces using different
network numbers. For example, if a router is set between a LAN and the Internet
(WAN), the router’s LAN and WAN addresses must be on different subnets. In the
following example, the LAN and WAN are on the same subnet. The LAN computers
cannot access the Internet because the router cannot route between networks.
Figure 158
Conflicting Computer IP Addresses Example
Conflicting Computer and Router IP Addresses Example
More than one device can not use the same IP address. In the following example,
the computer and the router’s LAN port both use 192.168.1.1 as the IP address.
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The computer cannot access the Internet. This problem can be solved by
assigning a different IP address to the computer or the router’s LAN port.
Figure 159
Conflicting Computer and Router IP Addresses Example
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A
PPENDIX
D
Wireless LANs
Wireless LAN Topologies
This section discusses ad-hoc and infrastructure wireless LAN topologies.
Ad-hoc Wireless LAN Configuration
The simplest WLAN configuration is an independent (Ad-hoc) WLAN that connects
a set of computers with wireless adapters (A, B, C). Any time two or more wireless
adapters are within range of each other, they can set up an independent network,
which is commonly referred to as an ad-hoc network or Independent Basic Service
Set (IBSS). The following diagram shows an example of notebook computers
using wireless adapters to form an ad-hoc wireless LAN.
Figure 160
Peer-to-Peer Communication in an Ad-hoc Network
BSS
A Basic Service Set (BSS) exists when all communications between wireless
clients or between a wireless client and a wired network client go through one
access point (AP).
Intra-BSS traffic is traffic between wireless clients in the BSS. When Intra-BSS is
enabled, wireless client
A
and
B
can access the wired network and communicate

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