NAME

ifconfig − configure network interface parameters

SYNOPSIS

ifconfiginterface[address_family][address[dest_address]][parameters]
[netmaskmask] [broadcastaddress][metricn]

ifconfiginterface[protocol_family]

DESCRIPTION

The ifconfig command is used to assign an address to a network interface and/or to configure network interface parameters.  The ifconfig command also 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 some other operating parameters.  When used without options, ifconfig displays the current configuration for a network interface.  If a protocol family is specified, ifconfig will report only the details specific to that protocol family. 

The interface parameter is a string of the form “name_unit”, for example, emd1.  The interface name −a is reserved and will cause the remainder of the arguments to be applied to each address of each interface in a sequential manner. 

Since an interface may receive transmissions using different protocols − each of which may require separate naming schemes − the parameters and addresses need to be interpreted according to the rules of a specified address_family parameter (which may change the interpretation of the remaining command line parameters).  Currently, only the Internet address_family is supported: ether and inet. 

If no address_family value is specified, inet will be assumed. 

For the DARPA Internet family (inet), the address is either a host name present in the host name data base [see hosts(4)], or a DARPA Internet address expressed in the Internet standard “dot notation”.  Typically, an Internet address specified in dot notation will consist of your system’s network number and the machine’s unique host number.  For example, a typical Internet address could be 192.9.200.44 where 192.9.200 is the “network number” and 44 is the machine’s “host number”. 

For the ether address family, the address is an Ethernet address represented as

x : x : x : x : x : x where x is a hexadecimal number between 0 and ff. 

If the dest_address parameter is supplied in addition to the address parameter, this specifies the address of the correspondent on the other end of a point-to-point link. 

OPTIONS

The following are valid values for parameters:

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. 

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, but this action will not automatically disable routes using this interface. 

trailers
(inet only) Enable the use of a trailer link-level encapsulation when sending (the default value).  If a network interface supports the trailers option (i.e., trailer encapsulation), the system will − when possible − encapsulate outgoing messages in a manner which will minimize the number of memory-to-memory copy operations performed by the receiver.  On networks which support the Address Resolution Protocol (ARP) − see arp(7); currently, arp applies only to the 10 Mb/s Ethernet − this flag indicates that the system should request that other systems should use trailer encapsulation when sending to this host.  Similarly, the trailer encapsulation technique will be used when sending to those other hosts which have made such requests. 

−trailers
Disable the use of the trailer link-level encapsulation technique. 

arp Enable the use of the Address Resolution Protocol (ARP) in mapping between network-level addresses and link-level addresses (the default value).  Currently, this is implemented for mapping between ARPA Internet addresses and 10Mb/s Ethernet addresses. 

−arp Disable the use of the Address Resolution Protocol. 

metric n
Set the routing metric of the interface to n; the default value is 0.  The routing metric is used by the routing protocol [routed(1M)].  Higher metrics have the effect of making a route less favorable: that is, the “metric” values are counted as additional hops to the destination network or host. 

netmask mask
(inet only) Specify how much of the “address space” 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 [see networks(4)].  The mask will contain 1 ’s for the bit positions in the 32-bit “address space” to be used for the network and subnet portions, and 0 ’s for the host portion.  The mask should contain at least the standard network portion; the subnet field should be adjacent to the network portion.  If a + (plus sign) is given for the netmask value, then the network number will looked up in the /etc/netmasks file. 

broadcast address
(inet only) Specify the address for representing broadcasts to the network.  The default broadcast address is the address with a host part of all 1 ’s.  A + (plus sign) given for the broadcast value causes the broadcast address to be reset to a default value appropriate for the (possibly new) Internet address and netmask parameters.  Note that the arguments of ifconfig are interpreted left to right: therefore the following two command lines may yield different sets of values to be assigned to the broadcast addresses for this interface:

      ifconfig −a netmask + broadcast +

      and

      ifconfig −a broadcast + netmask +

onepacket packet_size threshold
Enable the “one-packet” mode of operation which is used for any interface which cannot handle “back-to-back” packets. The keyword onepacket must be followed by two numeric parameters which specify the packet_size and threshold values, respectively.  If “small packet detection” is not desired, these two parameters should be set to zero.  [See tcp(7) for an explanation of the “one-packet” mode of operation.]

−onepacket
Disable the “one-packet” mode of operation.

EXAMPLES

If your workstation is not attached to an Ethernet, the emd1 interface should be marked down as follows:

ifconfig emd1 down

To print out the addressing information for each interface, use

ifconfig −a

To reset each interface’s broadcast address after the netmasks have been set correctly, use

ifconfig −a broadcast +

FILES

/dev/nit

/etc/netmasks

/etc/slattachcalls ifconfig to start the serial lines

SEE ALSO

arp(1M), netstat(1M), routed(1M), tcp(1M), arp(4), hosts(4), netmasks(4),
networks(4), strcf(4), arp(7), tcp(7). 

DIAGNOSTICS

There are diagnostic messages to indicate that the specified interface does not exist, that the requested address is unknown, or that the user is not privileged and tried to alter an interface’s configuration. 

NOTES

Only the super-user may modify the configuration of a network interface. 

The super-user is also the only one who may use the ether address_family. 

The trailers feature is machine-dependent and therefore its use is not recommended. 

The arp option is not applicable in the STREAMS environment.  The use of arp for an interface is specified in etc/strcf.  The arp driver will be opened when the STREAMS stack is built.