Chris Tyler - Fedora Linux

iwconfig will display current settings if no parameters are given:

# iwconfig

lo no wireless extensions.

eth0 no wireless extensions.

sit0 no wireless extensions.

wlan0 IEEE 802.11b ESSID:"" Nickname:"zd1201"

Mode:Managed Channel:6 Access Point: 00:90:4C:7E:00:29

Bit Rate:11 Mb/s

Retry:off RTS thr:off Fragment thr:off

Encryption key:off

Power Management:off

Link Quality:0/128 Signal level=60/128 Noise level:0/128

Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0

Tx excessive retries:0 Invalid misc:0 Missed beacon:0

Here you can see that this interface has associated with an access point with a MAC address of 00:90:4C:7E:00:29, and which is apparently an 802.11b network (11 Mb/s).

To scan for available networks, use iwlist with the scan argument:

# iwlist scan

lo Interface doesn't support scanning.

eth0 Interface doesn't support scanning.

sit0 Interface doesn't support scanning.

wlan0 Scan completed :

Cell 01 - Address: 00:90:4C:7E:00:29

ESSID:"fedorabook"

Mode:Master

Channel:11

Bit Rates:1 Mb/s

Bit Rates:2 Mb/s

Bit Rates:5.5 Mb/s

Bit Rates:11 Mb/s

Encryption key:off

Quality=60/128 Signal level=-76 dBm Noise level=-100 dBm

Cell 02 - Address: 00:87:29:13:c0:71

ESSID:"tylers"

Mode:Master

Channel:2

Bit Rates:1 Mb/s

Bit Rates:2 Mb/s

Bit Rates:5.5 Mb/s

Bit Rates:11 Mb/s

Bit Rates:18 Mb/s

Bit Rates:24 Mb/s

Bit Rates:36 Mb/s

Bit Rates:54 Mb/s

Encryption key:on

Quality=59/128 Signal level=-76 dBm Noise level=-99 dBm

To select which network wlan0 associates with, set the extended service set identifier (ESSID) of the interface:

# iwconfig wlan0 essid fedorabook

# iwconfig wlan0

wlan0 IEEE 802.11b ESSID:"fedorabook" Nickname:"zd1201"

Mode:Managed Channel:6 Access Point: 00:90:4C:7E:00:29

Bit Rate:11 Mb/s

Retry:off RTS thr:off Fragment thr:off

Encryption key:off

Power Management:off

Link Quality:0/128 Signal level=76/128 Noise level:0/128

Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0

Tx excessive retries:0 Invalid misc:0 Missed beacon:0

To disable an interface, turn it down using ifconfig :

# ifconfig wlan0 down

# ifconfig wlan0

wlan0 Link encap:Ethernet HWaddr 00:0C:2D:00:2B:DB

inet addr:192.168.9.37 Bcast:192.168.9.37 Mask:255.255.255.0

BROADCAST MULTICAST MTU:1500 Metric:1

RX packets:476 errors:0 dropped:0 overruns:0 frame:0

TX packets:18 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:1000

RX bytes:84965 (82.9 KiB) TX bytes:2922 (2.8 KiB)

Notice that the ifconfig display no longer shows the UP flag for the interface.

The netmask is used to determine which computers are on the local network, and which ones are remote and must therefore be reached through a gateway or router. These rules create the default routing table, which can be displayed with route :

# route

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

172.16.97.0 * 255.255.255.0 U 0 0 0 eth0

default 172.16.97.254 0.0.0.0 UG 0 0 0 eth0

Notice that two routes have been configured. The first one states that local machines (those with IP addresses starting with 172.16.97) can be reached directly on the local network (gateway * and no G in the Flags column), and the second entry states that packets destined to any other IP address are to be sent through the router 172.16.97.254 (which is on the local network and therefore directly reachable).

The default route can be removed and added back in, pointing to a different gateway/router:

# route delete default

# route add default gw 172.16.97.253

# route

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

172.16.97.0 * 255.255.255.0 U 0 0 0 eth0

default 172.16.97.253 0.0.0.0 UG 0 0 0 eth0

When the wlan0 interface is configured, a new route is added for hosts directly accessible through that interface:

# ifconfig wlan0 192.168.9.37

# route

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

172.16.97.0 * 255.255.255.0 U 0 0 0 eth0

192.168.9.0 * 255.255.255.0 U 0 0 0 wlan0

default 172.16.97.253 0.0.0.0 UG 0 0 0 eth0

If other networks are available through additional gateways, these can be configured by using route with the -net and netmask arguments. For example, if your corporate network 10.x.x.x in London were accessible through the gateway 192.168.9.1 on your wireless network, you could configure the route with this command:

# route add -net 10.0.0.0 netmask 255.0.0.0 gw 192.168.9.1

# route

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface

172.16.97.0 * 255.255.255.0 U 0 0 0 eth0

192.168.9.0 * 255.255.255.0 U 0 0 0 wlan0

10.0.0.0 192.168.9.1 255.0.0.0 UG 0 0 0 wlan0

default 172.16.97.253 0.0.0.0 UG 0 0 0 eth0

DNS resolution is controlled by the file /etc/resolv.conf , which looks something like this:

search fedorabook.com oreilly.com

nameserver 127.0.0.1

nameserver 216.183.93.224

There are three common option keywords used in this file:

search

A space- or tab-delimited list of domains to be searched when attempting to resolve a hostname without a domain component. In this example, if the DNS resolver were given the hostname bluesky , it would attempt to resolve the hostname bluesky.fedorabook.com , and if that failed, it would attempt to resolve bluesky.oreilly.com . There is a limit of six domains in the search list.

domain

A rarely used alternative to search that can specify only one domain. The domain and search options are mutually exclusive and cannot be used at the same time.