Learn the Linux Command Ifconfig

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Ifconfig configures kernel-resident network interfaces. At boot time it sets up interfaces as necessary. After that, it is usually only needed when debugging or when system tuning is needed.

The ifconfig command isn't installed by default on some distributions, including Ubuntu 19.04.

If no arguments are given, ifconfig displays the status of the currently active interfaces. If a single interface argument is given, it displays the status of the given interface only; if a single ​-a argument is given, it displays the status of all interfaces, even those that are down. Otherwise, it configures an interface.

Address Families

ifconfig

If the first argument after the interface name is recognized as the name of a supported address family, that address family is used for decoding and displaying all protocol addresses. Currently supported address families include inet (TCP/IP, default), inet6 (IPv6), ax25 (AMPR Packet Radio), ddp (Appletalk Phase 2), ipx (Novell IPX) and netrom (AMPR Packet radio).

Options

Use the following flags with this command:

  • interface: The name of the interface. This is usually a driver name followed by a unit number, for example eth0 for the first Ethernet interface.
  • up: This flag causes the interface to be activated. It is implicitly specified if an address is assigned to the interface.
  • down: This flag causes the driver for this interface to be shut down.
  • [-]arp: Enable or disable the use of the ARP protocol on this interface.
  • [-]promisc: Enable or disable the promiscuous mode of the interface. If selected, all packets on the network will be received by the interface.
  • [-]allmulti: Enable or disable all-multicast mode. If selected, all multicast packets on the network will be received by the interface.
  • metric N: This parameter sets the interface metric.
  • mtu N: This parameter sets the Maximum Transfer Unit of an interface.
  • netmask addr: Set the IP network mask for this interface. This value defaults to the usual class A, B or C network mask (as derived from the interface IP address), but it can be set to any value.
  • add addr/prefixlen: Add an IPv6 address to an interface.
  • del addr/prefixlen: Remove an IPv6 address from an interface.
  • tunnel aa.bb.cc.dd: Create a new SIT (IPv6-in-IPv4) device, tunneling to the given destination.
  • irq addr: Set the interrupt line used by this device. Not all devices can dynamically change their IRQ setting.
  • io_addr addr: Set the start address in I/O space for this device.
  • mem_start addr: Set the start address for shared memory used by this device. Only a few devices need this.
  • media type: Set the physical port or medium type to be used by the device. Not all devices can change this setting, and those that can vary in what values they support. Typical values for type are 10base2 (thin Ethernet), 10baseT (twisted-pair 10Mbps Ethernet), AUI (external transceiver) and so on. The special medium type of auto can be used to tell the driver to auto-sense the media. Again, not all drivers can do this.
  • [-]broadcast [addr]: If the address argument is given, set the protocol broadcast address for this interface. Otherwise, set (or clear) the IFF_BROADCAST flag for the interface.
  • [-]pointopoint [addr]: This keyword enables the point-to-point mode of an interface, meaning that it is a direct link between two machines with nobody else listening on it. 
  • hw class address: Set the hardware address of this interface, if the device driver supports this operation. The keyword must be followed by the name of the hardware class and the printable ASCII equivalent of the hardware address. Hardware classes currently supported include ether (Ethernet), ax25 (AMPR AX.25), ARCnet, and netrom (AMPR NET/ROM).
  • multicast: Set the multicast flag on the interface. This flag should not normally be needed as the drivers set the flag correctly themselves.
  • address: The IP address to be assigned to this interface.
  • txqueuelen length: Set the length of the transmit queue of the device. It is useful to set this to small values for slower devices with a high latency (modem links, ISDN) to prevent fast bulk transfers from disturbing interactive traffic like telnet too much.