IFCONFIG
NAME
ifconfig -- configure network interface parameters SYNOPSIS
ifconfig [-L] [-m] interface [create] [address_family] [address[/prefixlength] [dest_address]] [parameters] ifconfig interface destroy ifconfig -a [-L] [-d] [-m] [-u] [address_family] ifconfig -l [-d] [-u] [address_family] ifconfig [-L] [-b] [-d] [-m] [-u] ifconfig interface vlan vlan-tag vlandev iface ifconfig interface -vlandev iface ifconfig interface bonddev iface ifconfig interface -bonddev iface DESCRIPTION
Ifconfig is used to assign an address to a network interface and/or configure network interface parameters. Ifconfig must be used at boot time to define the network address of each interface present on a machine; it may also be used at a later time to redefine an interface's address or other operating parameters. The following options are available: address For the DARPA-Internet family, the address is either a host name present in the host name data base, hosts(5), or a DARPA Internet address expressed in the Internet standard ``dot notation''. It is also possible to use the CIDR notation (also known as the slash notation) to include the netmask. That is, one can specify an address like 192.168.0.1/16. address_family Specify the address family which affects interpretation of the remaining parameters. Since an interface can receive transmissions in differing protocols with different naming schemes, specifying the address family is recommended. The address or protocol families currently supported are ``inet'', ``inet6'', dest_address Specify the address of the correspondent on the other end of a point to point link. interface This parameter is a string of the form ``name unit'', for example, ``en0''. iface This parameter has the same encoding as the interface parameter. The following parameters may be set with ifconfig: add Another name for the alias parameter. Introduced for compatibility with BSD/OS. alias Establish an additional network address for this interface. This is sometimes useful when changing network numbers, and one wishes to accept packets addressed to the old interface. If the address is on the same subnet as the first network address for this interface, a netmask of 0xffffffff has to be specified. -alias Remove the network address specified. This would be used if you incorrectly specified an alias, or it was no longer needed. If you have incorrectly set an NS address having the side effect of specifying the host portion, removing all NS addresses will allow you to respecify the host portion. anycast (Inet6 only.) Specify that the address configured is an anycast address. Based on the current specification, only routers may configure anycast addresses. Anycast address will not be used as source address of any of outgoing IPv6 packets. arp Enable the use of the Address Resolution Protocol (arp(4)) in mapping between network level addresses and link level addresses (default). This is currently implemented for mapping between DARPA Internet addresses and IEEE 802 48-bit MAC addresses (Ethernet, FDDI, and Token Ring addresses). -arp Disable the use of the Address Resolution Protocol (arp(4)). bonddev iface If the interface is a bond pseudo device, associate physical interface iface with it. The bond pseudo device conforms to the IEEE 802.3ad Link Aggregation specification. If this is the first physical interface to be associated with the bond interface, the bond interface inherits the ethernet address from the physical interface. Physical interfaces that are added to the bond have their ethernet address re-programmed so that all members of the bond have the same ethernet address. If the physical interface is subsequently removed from the bond using -bonddev, a new ethernet address is chosen from the remaining interfaces, and all interfaces are re-programmed again with the new ethernet address. If no remaining interfaces exist, the bond interface's ethernet address is cleared. If the specified physical interface iface is not capable of having its ethernet address re-programmed, the bonddev command will fail. Once the physical interface iface is successfully associated with the bond interface, all received packets are diverted to the bond interface. The physical interface is no longer useable on its own, and remains that way until it is removed from the bond using -bonddev. It is possible that the specified interface iface is not capable of aggregating, and may remain unused until the operating conditions change. The link status of the bond interface depends on the state of link aggregation. If no active partner is detected, the link status will remain inactive. To monitor the 802.3ad Link Aggregation state, use the -b option. A physical interface that is associated with a vlan pseudo device cannot at the same time be associated with a bond pseudo device. A physical interface cannot be associated with more than one bond pseudo device at the same time. It is not possible to associate a bond with pseudo interfaces such as vlan. Only physical ethernet interfaces may be associated with a bond. -bonddev iface If the interface is a bond pseudo device, disassociate the physical interface iface from it. Before the interface is removed from the bond, the bond device announces to the link partner that the interface is now individual and no longer aggregatable. If the physical iface is the last interface in the bond, the bond interface clears its link address. broadcast (Inet only.) Specify the address to use to represent broadcasts to the network. The default broadcast address is the address with a host part of all 1's. debug Enable driver dependent debugging code; usually, this turns on extra console error logging. -debug Disable driver dependent debugging code. delete Another name for the -alias parameter. down Mark an interface ``down''. When an interface is marked ``down'', the system will not attempt to transmit messages through that interface. If possible, the interface will be reset to disable reception as well. This action does not automatically disable routes using the interface. ether Another name for the lladdr parameter. lladdr addr Set the link-level address on an interface. This can be used to e.g. set a new MAC address on an ethernet interface, though the mechanism used is not ethernet-specific. The address addr is specified as a series of colon-separated hex digits. If the interface is already up when this option is used, it will be briefly brought down and then brought back up again in order to ensure that the receive filter in the underlying ethernet hardware is properly reprogrammed. media type If the driver supports the media selection system, set the media type of the interface to type. Some interfaces support the mutually exclusive use of one of several different physical media connectors. For example, a 10Mb/s Ethernet interface might support the use of either AUI or twisted pair connectors. Setting the media type to ``10base5/AUI'' would change the currently active connector to the AUI port. Setting it to ``10baseT/UTP'' would activate twisted pair. Refer to the interfaces' driver specific documentation or man page for a complete list of the available types. mediaopt opts If the driver supports the media selection system, set the specified media options on the interface. The opts argument is a comma delimited list of options to apply to the interface. Refer to the interfaces' driver specific man page for a complete list of available options. -mediaopt opts If the driver supports the media selection system, disable the specified media options on the interface. tunnel src_addr dest_addr (IP tunnel devices only.) Configure the physical source and destination address for IP tunnel interfaces (gif(4)). The arguments src_addr and dest_addr are interpreted as the outer source/destination for the encapsulating IPv4/IPv6 header. deletetunnel Unconfigure the physical source and destination address for IP tunnel interfaces previously configured with tunnel. create Create the specified network pseudo-device. If the interface is given without a unit number, try to create a new device with an arbitrary unit number. If creation of an arbitrary device is successful, the new device name is printed to standard output. destroy Destroy the specified network pseudo-device. plumb Another name for the create parameter. Included for Solaris compatibility. unplumb Another name for the destroy parameter. Included for Solaris compatibility. metric n Set the routing metric of the interface to n, default 0. The routing metric is used by the routing protocol (routed(8)). Higher metrics have the effect of making a route less favorable; metrics are counted as addition hops to the destination network or host. mtu n Set the maximum transmission unit of the interface to n, default is interface specific. The MTU is used to limit the size of packets that are transmitted on an interface. Not all interfaces support setting the MTU, and some interfaces have range restrictions. netmask mask (Inet only.) Specify how much of the address to reserve for subdividing networks into sub-networks. The mask includes the network part of the local address and the subnet part, which is taken from the host field of the address. The mask can be specified as a single hexadecimal number with a leading `0x', with a dot-notation Internet address, or with a pseudo-network name listed in the network table networks(5). The mask contains 1's for the bit positions in the 32-bit address which are to be used for the network and subnet parts, and 0's for the host part. The mask should contain at least the standard network portion, and the subnet field should be contiguous with the network portion. The netmask can also be specified in CIDR notation after the address. See the address option above for more information. prefixlen len (Inet6 only.) Specify that len bits are reserved for subdividing networks into sub-networks. The len must be integer, and for syntactical reason it must be between 0 to 128. It is almost always 64 under the current IPv6 assignment rule. If the parameter is omitted, 64 is used. remove Another name for the -alias parameter. Introduced for compatibility with BSD/OS. link[0-2] Enable special processing of the link level of the interface. These three options are interface specific in actual effect, however, they are in general used to select special modes of operation. An example of this is to enable SLIP compression, or to select the connector type for some Ethernet cards. Refer to the man page for the specific driver for more information. -link[0-2] Disable special processing at the link level with the specified interface. up Mark an interface ``up''. This may be used to enable an interface after an ``ifconfig down''. It happens automatically when setting the first address on an interface. If the interface was reset when previously marked down, the hardware will be re-initialized. vlan vlan_tag vlandev iface If the interface is a vlan pseudo interface, set its vlan tag value to vlan_tag and associate it with the physical interface iface. The vlan_tag value is a 16-bit number that is used to create an 802.1Q vlan header for packets sent from the vlan interface. A packet that is transmitted through the vlan interface is sent using the specified physical interface iface with 802.1Q vlan encapsulation with the specified vlan_tag. A packet with 802.1Q encapsulation received by the physical interface is directed to the associated vlan interface with the matching vlan_tag. If there is no matching vlan interface, the packet is dropped. The vlan interface is assigned a copy of the parent interface's flags and the parent's ethernet address. If the vlan interface already has a physical interface associated with it, this command will fail. To change the association to another physical interface, the existing association must be cleared first using -vlandev. If the physical interface supports 802.1Q VLAN tagging in hardware, the vlan pseudo interface does not itself insert or remove the 802.1Q encapsulation header. Instead, the vlan_tag is passed out of band from the packet data. A physical interface that is associated with a bond pseudo device cannot at the same time be associated with a vlan interface. However, a physical interface can be associated with multiple vlan interfaces at the same time, as long as each of the vlan_tag values are unique. -vlandev iface If the driver is a vlan pseudo device, disassociate the physical interface iface from it. This breaks the link between the vlan interface and its parent, clears its vlan tag, flags and its link address. Ifconfig displays the current configuration for a network interface when no optional parameters are supplied. If a protocol family is specified, ifconfig will report only the details specific to that protocol family. If the driver supports the media selection system, the supported media list will be included in the output, regardless of whether the -m flag is passed or not. The -b option passed before the interface name will print the link aggregation state for bond pseudo devices. If -L flag is supplied, address lifetime is displayed for IPv6 addresses, as time offset string. Optionally, the -a flag may be used instead of an interface name. This flag instructs ifconfig to display information about all interfaces in the system. The -d flag limits this to interfaces that are down, and -u limits this to interfaces that are up. When no arguments are given, -a is implied. The -l flag may be used to list all available interfaces on the system, with no other additional information. Use of this flag is mutually exclusive with all other flags and commands, except for -d (only list interfaces that are down) and -u (only list interfaces that are up). Only the super-user may modify the configuration of a network interface. NOTES
The media selection system is relatively new and only some drivers support it (or have need for it). DIAGNOSTICS
Messages indicating the specified interface does not exist, the requested address is unknown, or the user is not privileged and tried to alter an interface's configuration. BUGS
IPv6 link-local addresses are required for several basic communication between IPv6 node. If they are deleted by ifconfig manually, the kernel might show very strange behavior. So, such manual deletions are strongly discouraged. SEE ALSO
netstat(1), netintro(4), rc(8), routed(8) HISTORY
The ifconfig command appeared in 4.2BSD. BSD July 15, 2004 BSD