ifconfig命令用来配置网络接口。
1. ifconfig默认会显示已经active的网络接口，
sh-# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:E7:06:00:00
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
Interrupt:40 Base address:0x2000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:1244 errors:0 dropped:0 overruns:0 frame:0
TX packets:1244 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:94792 (92.5 Kb) TX bytes:94792 (92.5 Kb)
sh-#
2. ifconfig也可以查看指定网卡的信息，
sh-# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0C:E7:06:00:00
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
Interrupt:40 Base address:0x2000
sh-#
3. 使用ifconfig命令修改IP地址，
sh-# ifconfig eth0 192.168.0.111 netmask 255.255.255.0
sh-#
sh-# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0C:E7:06:00:00
inet addr:192.168.0.111 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:92 errors:0 dropped:59 overruns:0 frame:0
TX packets:42 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:11155 (10.8 Kb) TX bytes:5318 (5.1 Kb)
Interrupt:40 Base address:0x2000
sh-#
sh-# ifconfig eth0:0 192.168.0.112 netmask 255.255.255.0
sh-#
4. 使用ifconfig配置一块新的网卡eth0:0，但是发现配置之后ping不通了，
sh-#
sh-# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:E7:06:00:00
inet addr:192.168.0.111 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:781 errors:0 dropped:480 overruns:0 frame:0
TX packets:141 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:106519 (104.0 Kb) TX bytes:20610 (20.1 Kb)
Interrupt:40 Base address:0x2000
eth0:0 Link encap:Ethernet HWaddr 00:0C:E7:06:00:00
inet addr:192.168.0.112 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Interrupt:40 Base address:0x2000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:1276 errors:0 dropped:0 overruns:0 frame:0
TX packets:1276 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:95816 (93.5 Kb) TX bytes:95816 (93.5 Kb)
sh-#
5. 禁用指定的网卡，
sh-# ifconfig eth0 down
[ 70.149765] star: star_stop(eth0)
sh-#
sh-# ifconfig
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:23 errors:0 dropped:0 overruns:0 frame:0
TX packets:23 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:736 (736.0 b) TX bytes:736 (736.0 b)
sh-#
6. 网卡被禁用后，可以使用ifconfig -a查看那些未激活的网卡信息，
sh-# ifconfig -a
eth0 Link encap:Ethernet HWaddr 00:0C:E7:06:00:00
BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:1547 errors:0 dropped:24 overruns:0 frame:0
TX packets:1030 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:2072118 (1.9 Mb) TX bytes:83723 (81.7 Kb)
Interrupt:40 Base address:0x2000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:151 errors:0 dropped:0 overruns:0 frame:0
TX packets:151 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:11968 (11.6 Kb) TX bytes:11968 (11.6 Kb)
sh-#
7. 如果要启动未激活的网卡，
sh-# ifconfig eth0 up
8. 使用ifconfig配置网卡的MAC地址，
sh-# ifconfig eth0 down
sh-# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:0C:E7:06:00:00
inet addr:192.168.0.174 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:259 errors:0 dropped:59 overruns:0 frame:0
TX packets:170 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:81474 (79.5 Kb) TX bytes:25650 (25.0 Kb)
Interrupt:40 Base address:0x2000
sh-#
可以看到，原来想将eth0禁止掉，但是eth0却仍然是激活的状态。
这是因为eth0一直处于忙碌的状态，需要先将对外的网络断掉，再试一下，
sh-# ifconfig eth0 down
[ 336.042795] star: star_stop(eth0)
sh-#
sh-# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:00:00:00:FC:CB
BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:389 errors:0 dropped:116 overruns:0 frame:0
TX packets:199 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:99361 (97.0 Kb) TX bytes:29032 (28.3 Kb)
Interrupt:40 Base address:0x2000
sh-#
接下来修改MAC地址，
sh-# ifconfig eth0 hw ether 00:00:00:00:FC:CB
sh-# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:00:00:00:FC:CB
BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:389 errors:0 dropped:116 overruns:0 frame:0
TX packets:199 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:99361 (97.0 Kb) TX bytes:29032 (28.3 Kb)
Interrupt:40 Base address:0x2000
sh-#
可以看到MAC地址修改成功，接下来再将eth0激活，
sh-# ifconfig eth0 up
[ 450.933630] star: star_open(eth0)
[ 450.934173] star: request interrupt vector=40
[ 450.938711] star: Internal PHY mode
sh-#
sh-# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:00:00:00:FC:CB
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:389 errors:0 dropped:116 overruns:0 frame:0
TX packets:199 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:99361 (97.0 Kb) TX bytes:29032 (28.3 Kb)
Interrupt:40 Base address:0x2000
sh-#
此时MAC地址已经正式修改完成了，插上网线，ping试试看，
sh-# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:00:00:00:FC:CB
inet addr:192.168.0.174 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:403 errors:0 dropped:118 overruns:0 frame:0
TX packets:220 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:101677 (99.2 Kb) TX bytes:32218 (31.4 Kb)
Interrupt:40 Base address:0x2000
sh-#
sh-# ping www.google.com
PING www.google.com (74.125.239.144) 56(84) bytes of data.
64 bytes from nuq05s02-in-f16.1e100.net (74.125.239.144): icmp_req=1 ttl=53 time=262 ms
64 bytes from nuq05s02-in-f16.1e100.net (74.125.239.144): icmp_req=2 ttl=53 time=252 ms
64 bytes from nuq05s02-in-f16.1e100.net (74.125.239.144): icmp_req=3 ttl=53 time=262 ms
^C
--- www.google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2017ms
rtt min/avg/max/mdev = 252.234/259.069/262.895/4.862 ms
sh-#
ifconfig所做的网络设定会在系统重启后消失，如果需要这些设定在系统启动时自动生效，
则需要将其配置到对应的网络配置文件中。
ifconfig命令的功能很强大，还有很多其它的功能，
在此不多说，有需要时再查资料。