IFCONFIG(8) BSD System Manager's Manual IFCONFIG(8)NAMEifconfig — configure network interface parameters
SYNOPSISifconfig [-L] [-m] [-r] interface [create] [address_family] [address
[dest_address]] [parameters]
ifconfig interface destroy
ifconfig-a [-L] [-d] [-m] [-r] [-u] [-v] [address_family]
ifconfig-l [-d] [-u] [address_family]
ifconfig [-L] [-d] [-m] [-r] [-u] [-v] [-C]
ifconfig interface vlan vlan-tag vlandev iface
ifconfig interface -vlandev iface
ifconfig interface bonddev iface
ifconfig interface -bonddev iface
ifconfig interface bondmode lacp | static
DESCRIPTION
The ifconfig utility is used to assign an address to a network interface
and/or configure network interface 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.
For the “inet6” family, it is also possible to specify the prefix
length using the slash notation, like ::1/128. See the prefixlen
parameter below for more information.
The link-level (“link”) address is specified as a series of
colon-separated hex digits. This can be used to e.g. set a new
MAC address on an ethernet interface, though the mechanism used
is not ethernet-specific. 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.
address_family
Specify the address family which affects interpretation of the
remaining parameters. Since an interface can receive transmis‐
sions in differing protocols with different naming schemes, spec‐
ifying the address family is recommended. The address or proto‐
col families currently supported are “inet”, “inet6”, and “link”.
The default is “inet”. “ether” and “lladdr” are synonyms for
“link”.
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”.
The following parameters may be set with ifconfig:
add Another name for the alias parameter. Introduced for compatibil‐
ity 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 non-conflicting netmask must be given. Usually
0xffffffff is most appropriate.
-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 (Eth‐
ernet, FDDI, and Token Ring addresses).
-arp Disable the use of the Address Resolution Protocol (arp(4)).
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.
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 hard‐
ware 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 mutu‐
ally exclusive use of one of several different physical media
connectors. For example, a 10Mbit/s Ethernet interface might
support the use of either AUI or twisted pair connectors. Set‐
ting 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 speci‐
fied 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.
rxcsum, txcsum
If the driver supports user-configurable checksum offloading,
enable receive (or transmit) checksum offloading on the inter‐
face. Some drivers may not be able to enable these flags inde‐
pendently of each other, so setting one may also set the other.
The driver will offload as much checksum work as it can reliably
support, the exact level of offloading varies between drivers.
-rxcsum, -txcsum
If the driver supports user-configurable checksum offloading,
disable receive (or transmit) checksum offloading on the inter‐
face. These settings may not always be independent of each
other.
tso If the driver supports tcp(4) segmentation offloading, enable TSO
on the interface. Some drivers may not be able to support TSO
for ip(4) and ip6(4) packets, so they may enable only one of
them.
-tso If the driver supports tcp(4) segmentation offloading, disable
TSO on the interface. It will always disable TSO for ip(4) and
ip6(4).
lro If the driver supports tcp(4) large receive offloading, enable
LRO on the interface.
-lro If the driver supports tcp(4) large receive offloading, disable
LRO on the interface.
av If supported by the driver, enable 802.1 AVB on the interface.
-av If supported by the driver, disable 802.1 AVB on the interface.
vlanmtu, vlanhwtag
If the driver offers user-configurable VLAN support, enable
reception of extended frames or tag processing in hardware,
respectively. Note that this must be issued on a physical inter‐
face associated with vlan(4), not on a vlan(4) interface itself.
-vlanmtu, -vlanhwtag
If the driver offers user-configurable VLAN support, disable
reception of extended frames or tag processing in hardware,
respectively.
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
unless the interface is renamed or destroyed in the same ifconfig
invocation.
destroy
Destroy the specified network pseudo-device.
plumb Another name for the create parameter. Included for Solaris com‐
patibility.
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 additional 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 restric‐
tions.
netmask mask
(Inet only.) Specify how much of the address to reserve for sub‐
dividing networks into sub-networks. The mask includes the net‐
work part of the local address and the subnet part, which is
taken from the host field of the address. The mask can be speci‐
fied 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 parame‐
ter is omitted, 64 is used.
The prefix can also be specified using the slash notation after
the address. See the address option above for more information.
remove Another name for the -alias parameter. Introduced for compati‐
bility 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, how‐
ever, they are in general used to select special modes of opera‐
tion. 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.
The following parameters are for ICMPv6 Neighbor Discovery Protocol.
Note that the address family keyword “inet6” is needed for them:
nud Perform network unreachability detection (NUD).
-nud Do not perform network unreachability detection (NUD).
ifdisabled
Disable all IPv6 communication on the interface.
-ifdisabled
Do not disable all IPv6 communication on the interface.
insecure
Disable the processing of Secure Neighbor Discovery (SEND).
-insecure
Do not disabled the processing of Secure Neighbor Discovery
(SEND).
The following parameters are specific to link aggregate interfaces:
bonddev iface
If the interface is a bond pseudo device, associate physical
interface iface with it. By default, the bond pseudo device is
in LACP (Link Aggregation Control Protocol) mode (see bondmode
below). In this mode, the 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 phys‐
ical 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 hav‐
ing 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 condi‐
tions 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 associ‐
ated with a bond.
-bonddev iface
If the interface is a bond pseudo device, disassociate the physi‐
cal 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.
bondmode lacp | static
If the interface is a bond pseudo device, this option will set
the mode on the bond interface. The two currently supported
modes are lacp and static. The default mode is lacp.
To enable static mode (and turn off LACP), specify static. In
static mode, a member interface is made an active part of the
link aggregate as long as the link status is active.
To re-enable LACP mode, specify lacp.
The following parameters are specific to IP tunnel interfaces, gif(4):
tunnel src_addr dest_addr
Configure the physical source and destination address for IP tun‐
nel interfaces. The arguments src_addr and dest_addr are inter‐
preted as the outer source/destination for the encapsulating
IPv4/IPv6 header.
-tunnel
Unconfigure the physical source and destination address for IP
tunnel interfaces previously configured with tunnel.
deletetunnel
Another name for the -tunnel parameter.
The following parameters are specific to bridge interfaces:
addm interface
Add the interface named by interface as a member of the bridge.
The interface is put into promiscuous mode so that it can receive
every packet sent on the network.
deletem interface
Remove the interface named by interface from the bridge. Promis‐
cuous mode is disabled on the interface when it is removed from
the bridge.
maxaddr size
Set the size of the bridge address cache to size. The default is
100 entries.
timeout seconds
Set the timeout of address cache entries to seconds seconds. If
seconds is zero, then address cache entries will not be expired.
The default is 240 seconds.
addr Display the addresses that have been learned by the bridge.
static interface-name address
Add a static entry into the address cache pointing to
interface-name. Static entries are never aged out of the cache
or re-placed, even if the address is seen on a different inter‐
face.
deladdr address
Delete address from the address cache.
flush Delete all dynamically-learned addresses from the address cache.
flushall
Delete all addresses, including static addresses, from the
address cache.
discover interface
Mark an interface as a “discovering” interface. When the bridge
has no address cache entry (either dynamic or static) for the
destination address of a packet, the bridge will forward the
packet to all member interfaces marked as “discovering”. This is
the default for all interfaces added to a bridge.
-discover interface
Clear the “discovering” attribute on a member interface. For
packets without the “discovering” attribute, the only packets
forwarded on the interface are broadcast or multicast packets and
packets for which the destination address is known to be on the
interface's segment.
learn interface
Mark an interface as a “learning” interface. When a packet
arrives on such an interface, the source address of the packet is
entered into the address cache as being a destination address on
the interface's segment. This is the default for all interfaces
added to a bridge.
-learn interface
Clear the “learning” attribute on a member interface.
stp interface
Enable Spanning Tree protocol on interface. The if_bridge(4)
driver has support for the IEEE 802.1D Spanning Tree protocol
(STP). Spanning Tree is used to detect and remove loops in a
network topology.
-stp interface
Disable Spanning Tree protocol on interface. This is the default
for all interfaces added to a bridge.
maxage seconds
Set the time that a Spanning Tree protocol configuration is
valid. The default is 20 seconds. The minimum is 6 seconds and
the maximum is 40 seconds.
fwddelay seconds
Set the time that must pass before an interface begins forwarding
packets when Spanning Tree is enabled. The default is 15 sec‐
onds. The minimum is 4 seconds and the maximum is 30 seconds.
hellotime seconds
Set the time between broadcasting of Spanning Tree protocol con‐
figuration messages. The hello time may only be changed when
operating in legacy stp mode. The default is 2 seconds. The
minimum is 1 second and the maximum is 2 seconds.
priority value
Set the bridge priority for Spanning Tree. The default is 32768.
The minimum is 0 and the maximum is 61440.
ifpriority interface value
Set the Spanning Tree priority of interface to value. The
default is 128. The minimum is 0 and the maximum is 240.
ifpathcost interface value
Set the Spanning Tree path cost of interface to value. The
default is calculated from the link speed. To change a previ‐
ously selected path cost back to automatic, set the cost to 0.
The minimum is 1 and the maximum is 200000000.
ifmaxaddr interface size
Set the maximum number of hosts allowed from an interface, pack‐
ets with unknown source addresses are dropped until an existing
host cache entry expires or is removed. Set to 0 to disable.
The following parameters are specific to vlan interfaces:
vlan vlan_tag
Set the VLAN tag value to vlan_tag. This value is a 16-bit num‐
ber which is used to create an 802.1Q VLAN header for packets
sent from the vlan(4) interface. Note that vlan and vlandev must
both be set at the same time.
vlandev iface
Associate the physical interface iface with a vlan(4) interface.
Packets transmitted through the vlan(4) interface will be
diverted to the specified physical interface iface with 802.1Q
VLAN encapsulation. Packets with 802.1Q encapsulation received
by the parent interface with the correct VLAN tag will be
diverted to the associated vlan(4) pseudo-interface. The vlan(4)
interface is assigned a copy of the parent interface's flags and
the parent's ethernet address. The vlandev and vlan must both be
set at the same time. If the vlan(4) 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.
Note: if the hardware tagging capability is set on the parent
interface, the vlan(4) pseudo interface's behavior changes: the
vlan(4) interface recognizes that the parent interface supports
insertion and extraction of VLAN tags on its own (usually in
firmware) and that it should pass packets to and from the parent
unaltered.
-vlandev [iface]
If the driver is a vlan(4) pseudo device, disassociate the parent
interface from it. This breaks the link between the vlan(4)
interface and its parent, clears its VLAN tag, flags and its link
address and shuts the interface down. The iface argument is use‐
less and hence deprecated.
The ifconfig utility 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 pro‐
tocol family.
If the -m flag is passed before an interface name, ifconfig will display
the capability list and all of the supported media for the specified
interface.
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).
The -v flag may be used to get more verbose status for an interface.
The -C flag may be used to list all of the interface cloners available on
the system, with no additional information. Use of this flag is mutually
exclusive with all other flags and commands.
The -r flag may be used to show additional information related to the
count of route references on the network interface.
For bridge interfaces, the list of addresses learned by the bridge is not
shown when displaying information about all interfaces except when the -v
flag is used.
Only the super-user may modify the configuration of a network interface.
NOTES
The media selection system is relatively new and only some drivers sup‐
port it (or have need for it).
EXAMPLES
Assign the IPv4 address 192.0.2.10, with a network mask of 255.255.255.0,
to the interface en0:
# ifconfig en0 inet 192.0.2.10 netmask 255.255.255.0
Add the IPv4 address 192.0.2.45, with the CIDR network prefix /28, to the
interface en0, using add as a synonym for the canonical form of the
option alias:
# ifconfig en0 inet 192.0.2.45/28 add
Remove the IPv4 address 192.0.2.45 from the interface en0:
# ifconfig en0 inet 192.0.2.45 -alias
Add the IPv6 address 2001:DB8:DBDB::123/48 to the interface en0:
# ifconfig en0 inet6 2001:db8:bdbd::123 prefixlen 48 alias
Note that lower case hexadecimal IPv6 addresses are acceptable.
Remove the IPv6 address added in the above example, using the / character
as shorthand for the network prefix, and using delete as a synonym for
the canonical form of the option -alias:
# ifconfig en0 inet6 2001:db8:bdbd::123/48 delete
Configure the interface en1, to use 100baseTX, full duplex Ethernet media
options:
# ifconfig en1 media 100baseTX mediaopt full-duplex
Create the software network interface gif1:
# ifconfig gif1 create
Destroy the software network interface gif1:
# ifconfig gif1 destroy
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.
SEE ALSOnetstat(1), netintro(4), sysctl(8)HISTORY
The ifconfig utility appeared in 4.2BSD.
BUGS
Basic IPv6 node operation requires a link-local address on each interface
configured for IPv6. Normally, such an address is automatically config‐
ured by the kernel on each interface added to the system; this behaviour
may be disabled by setting the sysctl MIB variable
net.inet6.ip6.auto_linklocal to 0.
If you delete such an address using ifconfig, the kernel may act very
odd. Do this at your own risk.
BSD June 20, 2008 BSD
