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Appendix C Setting up Your Computer’s IP Address
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191
• If you have a static IP address, enter
static
in the
BOOTPROTO=
field. Type
IPADDR
= followed by the IP address (in dotted decimal notation) and type
NETMASK
= followed by the subnet mask. The following example shows an
example where the static IP address is
192.168.1.10 and the subnet mask is
255.255.255.0.
Figure 125
Red Hat 9.0: Static IP Address Setting in ifconfig-eth0
2
If you know your DNS server IP address(es), enter the DNS server information in
the
resolv.conf
file in the
/etc
directory. The following figure shows an example
where two DNS server IP addresses are specified.
Figure 126
Red Hat 9.0: DNS Settings in resolv.conf
3
After you edit and save the configuration files, you must restart the network card.
Enter
./network restart
in the
/etc/rc.d/init.d
directory. The following figure
shows an example.
Figure 127
Red Hat 9.0: Restart Ethernet Card
DEVICE=eth0
ONBOOT=yes
BOOTPROTO=static
IPADDR=
192.168.1.10
NETMASK=
255.255.255.0
USERCTL=no
PEERDNS=yes
TYPE=Ethernet
nameserver 172.23.5.1
nameserver 172.23.5.2
[root@localhost init.d]# network restart
Shutting down interface eth0:
[OK]
Shutting down loopback interface:
[OK]
Setting network parameters:
[OK]
Bringing up loopback interface:
[OK]
Bringing up interface eth0:
[OK]
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21.0.1
Verifying Settings
Enter
ifconfig
in a terminal screen to check your TCP/IP properties.
Figure 128
Red Hat 9.0: Checking TCP/IP Properties
[root@localhost]# ifconfig
eth0
Link encap:Ethernet HWaddr 00:50:BA:72:5B:44
inet addr:172.23.19.129 Bcast:172.23.19.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:717 errors:0 dropped:0 overruns:0 frame:0
TX packets:13 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:730412 (713.2 Kb) TX bytes:1570 (1.5 Kb)
Interrupt:10 Base address:0x1000
[root@localhost]#
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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 stations (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 129
Peer-to-Peer Communication in an Ad-hoc Network
BSS
A Basic Service Set (BSS) exists when all communications between wireless
stations or between a wireless station and a wired network client go through one
access point (AP).
Intra-BSS traffic is traffic between wireless stations in the BSS. When Intra-BSS is
enabled, wireless station A and B can access the wired network and communicate
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Appendix D Wireless LANs
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194
with each other. When Intra-BSS is disabled, wireless station A and B can still
access the wired network but cannot communicate with each other.
Figure 130
Basic Service Set
ESS
An Extended Service Set (ESS) consists of a series of overlapping BSSs, each
containing an access point, with each access point connected together by a wired
network. This wired connection between APs is called a Distribution System (DS).
This type of wireless LAN topology is called an Infrastructure WLAN. The Access
Points not only provide communication with the wired network but also mediate
wireless network traffic in the immediate neighborhood.
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195
An ESSID (ESS IDentification) uniquely identifies each ESS. All access points and
their associated wireless stations within the same ESS must have the same ESSID
in order to communicate.
Figure 131
Infrastructure WLAN
Channel
A channel is the radio frequency(ies) used by IEEE 802.11a/b/g wireless devices.
Channels available depend on your geographical area. You may have a choice of
channels (for your region) so you should use a different channel than an adjacent
AP (access point) to reduce interference. Interference occurs when radio signals
from different access points overlap causing interference and degrading
performance.
Adjacent channels partially overlap however. To avoid interference due to overlap,
your AP should be on a channel at least five channels away from a channel that an
adjacent AP is using. For example, if your region has 11 channels and an adjacent
AP is using channel 1, then you need to select a channel between 6 or 11.
RTS/CTS
A hidden node occurs when two stations are within range of the same access
point, but are not within range of each other. The following figure illustrates a
hidden node. Both stations (STA) are within range of the access point (AP) or
19216811.live