ifconfig Command#

The ifconfig command stands for interface configuration and is used to view and change the configuration of network interfaces on a system.

Syntax#

ifconfig [-a] [-v] [-s] <interface> [[<AF>] <address>]
  [add <address>[/<prefixlen>]]
  [del <address>[/<prefixlen>]]
  [[-]broadcast [<address>]]  [[-]pointopoint [<address>]]
  [netmask <address>]  [dstaddr <address>]  [tunnel <address>]
  [outfill <NN>] [keepalive <NN>]
  [hw <HW> <address>]  [mtu <NN>]
  [[-]trailers]  [[-]arp]  [[-]allmulti]
  [multicast]  [[-]promisc]
  [mem_start <NN>]  [io_addr <NN>]  [irq <NN>]  [media <type>]
  [txqueuelen <NN>]
  [[-]dynamic]
  [up|down] ...

Parameters#

• (none), -a: Display information for all network interfaces, even if they are turned off.
• -s: Display a brief list in the same format as the netstat -i command.
• -v: Verbose mode, displays detailed information on certain error conditions.
• interface: Interface name, usually the driver name followed by a unit number, such as the first Ethernet interface eth0. If kernel supports alias interfaces, a first alias for eth0 can be specified with eth0:0, to use them to assign a second address, to delete an alias interface, use ifconfig eth0:0 down. Note that if the first (main) interface is deleted, all aliases will be removed for each range with the same address/netmask combination on the same network.
• up: This flag activates the interface. If an address has been assigned to the interface, it is implicitly specified.
• down: This flag causes the interface's driver to be disabled.
• [-]arp: Enable (- prefix disables) the use of the ARP protocol on this interface.
• [-]promisc: Enable (- prefix disables) promiscuous mode for the interface. When promiscuous mode is enabled, the interface will receive all packets on the network.
• [-]allmulti: Enable (- prefix disables) all-multicast mode. When all-multicast mode is enabled, the interface will receive all multicast packets on the network.
• metric N: This parameter sets the interface metric, which the interface uses to make routing decisions. N must be an integer between 0 and 4294967295.
• mtu N: This parameter is used to set the maximum transmission unit for the interface, which limits the maximum packet size the interface can transmit.
• dstaddr address: Set the remote IP address for a point-to-point link (e.g., PPP). This keyword is now deprecated; please use the pointopoint keyword instead.
• netmask address: Set the IP network mask for the interface. This value defaults to the standard A, B, or C class network masks derived from the interface IP address, but it can be set to any value.
• add address/prefixlen: Add an IPv6 address to the interface.
• del address/prefixlen: Remove an IPv6 address from the interface.
• tunnel aa.bb.cc.dd: Create a new SIT (IPv6-in-IPv4) device, tunneled to the given destination.
• irq address: Set the interrupt line used by this device. Not all devices can dynamically change their IRQ settings.
• io_addr address: Set the starting address in this device's I/O space.
• mem_start address: Set the starting address for the shared memory used by this device. Only a few devices require this feature.
• media type: Set the physical port or media type for the device. Not all devices can change this setting, and some devices can change the values they support. Typical values for type are 10base2 (thin coaxial cable network), 10baseT (twisted pair 10 Mbps Ethernet), AUI transceiver, etc. The special media type auto tells the driver to autonegotiate the media. Not all drivers can perform this operation.
• [-]broadcast [address]: If an address parameter is specified, it sets the protocol broadcast address for the interface; otherwise, it sets (with - prefix clears) the interface's IFF_BROADCAST flag.
• [-]pointopoint [address]: This keyword enables the interface's point-to-point mode, meaning it is a direct link between two machines with no one else listening in. If an address parameter is also provided, set the protocol address at the other end of the link as with the obsolete dstaddr keyword; otherwise, set or clear the interface's IFF POINTOPOINT flag.
• hw class address: If supported by the device driver, set the hardware address for this interface. The keyword must be followed by the name of the hardware class and its printable ASCII equivalent of the hardware address. Currently supported hardware classes include ether (Ethernet), ax25 (AMPR AX.25), ARCnet and netrom (AMPR NET/ROM).
• multicast: Set the multicast flag on the interface. This is usually unnecessary since the driver will correctly set this flag.
• address: IP address assigned to the interface.
• txqueuelen length: Set the length of the device's transmit queue. For slower devices with higher latency (e.g., connections over modems or ISDN), setting it to a smaller value is very useful to prevent too much interference from rapid bulk transfers with interactive communication such as telnet.

Hardware Types#

loop (Local Loopback), slip (Serial Line IP), cslip (VJ Serial Line IP), slip6 (6-bit Serial Line IP), cslip6 (VJ 6-bit Serial Line IP), adaptive (Adaptive Serial Line IP), ash (Ash), ether (Ethernet), ax25 (AMPR AX.25), netrom (AMPR NET/ROM), rose (AMPR ROSE), tunnel (IPIP Tunnel), ppp (Point-to-Point Protocol), hdlc ((Cisco)-HDLC), lapb (LAPB), arcnet (ARCnet), dlci (Frame Relay DLCI), frad (Frame Relay Access Device), sit (IPv6-in-IPv4), fddi (Fiber Distributed Data Interface), hippi (HIPPI), irda (IrLAP), ec (Econet), x25 (generic X.25), eui64 (Generic EUI-64)

Address Families#

unix (UNIX Domain), inet (DARPA Internet), inet6 (IPv6), ax25 (AMPR AX.25), netrom (AMPR NET/ROM), rose (AMPR ROSE), ipx (Novell IPX), ddp (Appletalk DDP), ec (Econet), ash (Ash), x25 (CCITT X.25)

Examples#

Display network device information.

ifconfig

Start and stop a specific network card.

ifconfig eth0 down
ifconfig eth0 up

Configure and delete an IPv6 address for a network card.

ifconfig eth0 add 33ffe:3240:800:1005::2/64
ifconfig eth0 del 33ffe:3240:800:1005::2/64

To change the MAC address, first disable the network card, then modify the MAC address, and finally enable the network card.

ifconfig eth1 hw ether 00:1D:1C:1D:1E
ifconfig eth1 up

Assign an IP address to the network card, and include the subnet mask and broadcast address.

ifconfig eth0 192.168.1.56 netmask 255.255.255.0 broadcast 192.168.1.255

Enable and disable the ARP protocol.

ifconfig eth0 arp
ifconfig eth0 -arp

Set the Maximum Transmission Unit MTU.

ifconfig eth0 mtu 1500

Every Day One Question#

Reference#