inet6 addr: fe80::20c:2dff:fe00:2bdb/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1 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:268 (268.0 b) TX bytes:2922 (2.8 KiB)
3.2.1.3.1. Configuring wireless networks from the command line
For wireless interfaces, there are two additional commands that are useful for configuration: iwconfig , which sets wireless parameterssuch as the channel, encryption, and ESSIDand iwlist , which can be used to scan for available networks.
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 Channeclass="underline" 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 leveclass="underline" 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
Channeclass="underline" 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
Channeclass="underline" 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 Channeclass="underline" 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 leveclass="underline" 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.
3.2.1.3.2. Netmasks and routing
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).