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USERCTL=no
PEERDNS=yes
TYPE=Ethernet
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 167
Red Hat 9.0: DNS Settings in resolv.conf
nameserver 172.23.5.1
nameserver 172.23.5.2
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 168
Red Hat 9.0: Restart Ethernet Card
[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]
34.1.2 Verifying Settings
Enter ifconfig in a terminal screen to check your TCP/IP properties.
Figure 169
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)
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Interrupt:10 Base address:0x1000
[root@localhost]#
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Appendix 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 170
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 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.
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Figure 171
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.
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.
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Figure 172
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 wireless
gateway, but out-of-range of each other, so they cannot "hear" each other, that is, they do not know if the channel is
currently being used. Therefore, they are considered hidden from each other.
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