Linux "ifconfig" Command Line Options and Examples
configure a network interface
Ifconfig is used to configure the kernel-resident network interfaces. It is used at boot time to set up interfaces as necessary. After that, it is usually only needed when debugging or when system tuning is needed.
ifconfig [-v] [-a] [-s] [interface]
ifconfig [-v] interface [aftype] options | address ...
Command Line Options:
display all interfaces which are currently available, even if down
ifconfig -a ...
display a short list (like netstat -i)
ifconfig -s ...
interfaceThe name of the interface. This is usually a driver name followed by a unit number, for example eth0 for the first Ethernetinterface. If your kernel supports alias interfaces, you can specify them with syntax like eth0:0 for the first alias of eth0.You can use them to assign more addresses. To delete an alias interface use ifconfig eth0:0 down. Note: for every scope (i.e.same net with address/netmask combination) all aliases are deleted, if you delete the first (primary).up This flag causes the interface to be activated. It is implicitly specified if an address is assigned to the interface; youcan suppress this behavior when using an alias interface by appending an - to the alias (e.g. eth0:0-). It is also sup‐pressed when using the IPv4 0.0.0.0 address as the kernel will use this to implicitly delete alias interfaces.down This flag causes the driver for this interface to be shut down.
ifconfig -v ...
Enable or disable the use of the ARP protocol on this interface.
ifconfig -]arp ...
Enable or disable the promiscuous mode of the interface. If selected, all packets on the network will be received by theinterface.
ifconfig -]promisc ...
Enable or disable all-multicast mode. If selected, all multicast packets on the network will be received by the interface.mtu N This parameter sets the Maximum Transfer Unit (MTU) of an interface.dstaddr addrSet the remote IP address for a point-to-point link (such as PPP). This keyword is now obsolete; use the pointopoint keywordinstead.netmask addrSet the IP network mask for this interface. This value defaults to the usual class A, B or C network mask (as derived fromthe interface IP address), but it can be set to any value.add addr/prefixlenAdd an IPv6 address to an interface.del addr/prefixlenRemove an IPv6 address from an interface.tunnel ::aa.bb.cc.ddCreate a new SIT (IPv6-in-IPv4) device, tunnelling to the given destination.irq addrSet the interrupt line used by this device. Not all devices can dynamically change their IRQ setting.io_addr addrSet the start address in I/O space for this device.mem_start addrSet the start address for shared memory used by this device. Only a few devices need this.media typeSet the physical port or medium type to be used by the device. Not all devices can change this setting, and those that canvary in what values they support. Typical values for type are 10base2 (thin Ethernet), 10baseT (twisted-pair 10Mbps Ether‐net), AUI (external transceiver) and so on. The special medium type of auto can be used to tell the driver to auto-sense themedia. Again, not all drivers can do this.
ifconfig -]allmulti ...
If the address argument is given, set the protocol broadcast address for this interface. Otherwise, set (or clear) theIFF_BROADCAST flag for the interface.
ifconfig -]broadcast ...
This keyword enables the point-to-point mode of an interface, meaning that it is a direct link between two machines withnobody else listening on it.If the address argument is also given, set the protocol address of the other side of the link, just like the obsolete dstaddrkeyword does. Otherwise, set or clear the IFF_POINTOPOINT flag for the interface.hw class addressSet the hardware address of this interface, if the device driver supports this operation. The keyword must be followed by thename of the hardware class and the printable ASCII equivalent of the hardware address. Hardware classes currently supportedinclude ether (Ethernet), ax25 (AMPR AX.25), ARCnet and netrom (AMPR NET/ROM).multicastSet the multicast flag on the interface. This should not normally be needed as the drivers set the flag correctly themselves.addressThe IP address to be assigned to this interface.txqueuelen lengthSet the length of the transmit queue of the device. It is useful to set this to small values for slower devices with a highlatency (modem links, ISDN) to prevent fast bulk transfers from disturbing interactive traffic like telnet too much.NOTESSince kernel release 2.2 there are no explicit interface statistics for alias interfaces anymore. The statistics printed for theoriginal address are shared with all alias addresses on the same device. If you want per-address statistics you should add explicitaccounting rules for the address using the iptables(8) command.Interrupt problems with Ethernet device drivers fail with EAGAIN (SIOCSIIFLAGS: Resource temporarily unavailable) it is most likely ainterrupt conflict. See http://www.scyld.com/expert/irq-conflict.html for more information.FILES/proc/net/dev/proc/net/if_inet6BUGSIfconfig uses the ioctl access method to get the full address information, which limits hardware addresses to 8 bytes. BecauseInfiniband hardware address has 20 bytes, only the first 8 bytes are displayed correctly. Please use ip link command from iproute2package to display link layer informations including the hardware address.While appletalk DDP and IPX addresses will be displayed they cannot be altered by this command.
ifconfig -]pointopoint ...