[Comprehensive explanation of Linux commands] 135. Detailed explanation and usage examples of Linux ifconfig command

ifconfig

The ifconfig command is used to configure and display the network parameters of the network interface in the Linux kernel. The network card information configured with the ifconfig command will no longer exist after the network card is restarted and the machine is restarted. If you want to permanently store the above configuration information in the computer, you need to modify the configuration file of the network card.

grammar

ifconfig(参数)

Parameter Description:

• add<address>: Set the IP address of the network device IPv6;
• del<address>: Delete the IP address of the network device IPv6;
• down: Shut down the specified network device;
• <hw<network device type><hardware address>: Set the type and hardware address of the network device;
• io_addr<I/O address>: Set the I/O address of the network device;
• irq<IRQ address>: Set the IRQ of the network device;
• media<network media type>: Set the media type of the network device;
• mem_start <memory address>: Set the starting address occupied by the network device in the main memory;
• metric<number>: Specifies the number to be added when calculating the number of packet transmissions;
• mtu<byte>: Set the MTU of the network device;
• netmask<subnet mask>: Set the subnet mask of the network device;
• tunnel<address>: establish the tunnel communication address between IPv4 and IPv6;
• up: Start the specified network device;
• broadcast<address>: Treat the data packet sent to the specified address as a broadcast packet;
• pointopoint <address>: Establish a direct connection with the network device at the specified address. This mode has a confidentiality function;
• promisc: close or enable the promiscuous mode of the specified network device;
• IP address: Specify the IP address of the network device;
• Network device: Specify the name of the network device.

Example

Display network device information (activated):

[root@localhost ~]# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:16:3E:00:1E:51  
          inet addr:10.160.7.81  Bcast:10.160.15.255  Mask:255.255.240.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:61430830 errors:0 dropped:0 overruns:0 frame:0
          TX packets:88534 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:3607197869 (3.3 GiB)  TX bytes:6115042 (5.8 MiB)

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:56103 errors:0 dropped:0 overruns:0 frame:0
          TX packets:56103 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:5079451 (4.8 MiB)  TX bytes:5079451 (4.8 MiB)

illustrate:

• eth0 represents the first network card, where HWaddr represents the physical address of the network card. You can see that the current physical address (MAC address) of this network card is 00:16:3E:00:1E:51.
• inet addr is used to represent the IP address of the network card. The IP address of this network card is 10.160.7.81, the broadcast address Bcast:10.160.15.255, and the mask address Mask:255.255.240.0.
• lo represents the return address of the host. This is generally used to test a network program, but does not want users on the LAN or external network to view it. It can only run and view the network interface used on this host. For example, specify the return address of the httpd server and enter 127.0.0.1 in the browser to see your WEB website. But only you can see it, other hosts or users on the LAN have no way of knowing.
• First line: Connection type: Ethernet HWaddr (hardware MAC address).
• The second line: the IP address, subnet, and mask of the network card.
• The third line: UP (represents that the network card is on) RUNNING (represents that the network cable of the network card is connected) MULTICAST (supports multicast) MTU: 1500 (maximum transmission unit): 1500 bytes.
• The fourth and fifth rows: statistics on receiving and sending data packets.
• The seventh line: statistical information on the number of data bytes received and sent.

Start and shut down the specified network card:

ifconfig eth0 up
ifconfig eth0 down

Ifconfig eth0 up is to start the network card eth0, and ifconfig eth0 down is to shut down the network card eth0. Be careful when logging into a Linux server via SSH. Once it is turned off, it cannot be turned on unless you have multiple network cards.

Configure and delete IPv6 addresses for network cards:

ifconfig eth0 add 33ffe:3240:800:1005::2/64    # 为网卡 eth0 配置 IPv6 地址
ifconfig eth0 del 33ffe:3240:800:1005::2/64    # 为网卡 eth0 删除 IPv6 地址

Use ifconfig to modify the MAC address:

ifconfig eth0 hw ether 00:AA:BB:CC:dd:EE

Configure IP address:

[root@localhost ~]# ifconfig eth0 192.168.2.10
[root@localhost ~]# ifconfig eth0 192.168.2.10 netmask 255.255.255.0
[root@localhost ~]# ifconfig eth0 192.168.2.10 netmask 255.255.255.0 broadcast 192.168.2.255

Enable and disable ARP protocol:

ifconfig eth0 arp    # 开启网卡 eth0 的 ARP 协议
ifconfig eth0 -arp   # 关闭网卡 eth0 的 ARP 协议

Set the maximum transmission unit:

ifconfig eth0 mtu 1500    # 设置能通过的最大数据包大小为 1500 bytes

Other examples:

ifconfig   # 处于激活状态的网络接口
ifconfig -a  # 所有配置的网络接口，不论其是否激活
ifconfig eth0  # 显示 eth0 的网卡信息

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