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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP Administration and Troubleshooting Utilities and Protocols

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TCP/IP Network Status Utility (netstat)
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Miscellaneous TCP/IP Troubleshooting Protocols: Echo, Discard, Character Generator, Quote Of The Day, Active Users, Daytime, Time
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TCP/IP Configuration Utilities (ipconfig, winipcfg and ifconfig)
(Page 2 of 5)

ifconfig Syntaxes, Options and Parameters

Table 304 provides a simplified summary of the different functions that ifconfig can perform, and the syntaxes that are used to specify each in a typical UNIX implementation (NetBSD in this case). Table 305 describes the common options and parameters that can be used for many of these different modes. When ifconfig is used to modify an interface’s configuration, this is done by setting any of several dozen configuration parameters, using the syntax shown in the last row of Table 304; I have provided a brief description of some sample parameters in Table 306 (see your ifconfig documentation for a complete list).

Table 304: Typical UNIX ifconfig Syntaxes, Options and Parameters

Syntax, Options and Parameters


ifconfig [-L] [-m] <interface>

When ifconfig is called with just an interface specification and no other options (other than possibly “-L” and “-m”), it displays the configuration information for that network interface.

Note that entering “ifconfig” by itself with no interface just causes help information for the parameter to be displayed; to see all interfaces, the “-a” parameter should be used.

ifconfig -a [-L] [-m] [-b] [-d]
[-u] [-s] [<family>]

Displays information about all the interfaces on the host. The output may be restricted using the universal parameters shown, or by specifying an address family (see Table 305).

ifconfig -l [-b] [-d] [-u] [-s]

Lists all available interfaces on the system.

ifconfig <interface> create

Creates the specified logical network interface on the host, which is then configured using the syntax shown in the last row of this table. Note that some variations of UNIX allow certain parameters to be set at the time of creation.

ifconfig <interface> destroy

Destroys the specified logical interface.

ifconfig <interface> [<family>]
[<address> [<dest_address>]]

Configures parameters for a particular interface on the host. If the address is being set, it is the first parameter specified, after the optional address family, if present. The “<dest_address>” is used to specify a destination address for a point-to-point link. After this, any of several dozen parameters may be specified for the interface, some of which are shown in Table 306.

Table 305: Typical UNIX ifconfig Universal Options and Parameters

Option / Parameter



Displays the address lifetime for IPv6 addresses.


Displays all supported media for the interface.


Limits the display of interface information to broadcast interfaces.


Shows only interfaces that are presently down (disabled).


Shows only interfaces that are presently up (operational).


Shows only interfaces that may be connected.


Specifies a particular address family, either to limit output or indicate what address type is being configured. The value “inet” is used for IPv4 and “inet6” for IPv6.

Table 306: Typical UNIX ifconfig Interface Configuration Parameters



alias / -alias

Establishes or removes a network address alias.

arp / -arp

Enables / disables the use of ARP on this interface.


Removes the specified network address.


Marks an interface as being “down”, disabling it.

media <type>

Sets the media type of the interface to a particular value.

mtu <n>

Sets the maximum transmission unit (MTU) of the interface.

netmask <mask>

Sets the network or subnet mask for the interface’s address.

prefixlen <n>

Same as “netmask” but allows the mask to be specified using a CIDR-style prefix length.


Sets an interface “up”, enabling it.

Note: Since creating, destroying or modifying interfaces can cause a host to stop working properly, administrative (super-user) rights are generally required on most systems in order to do anything with ifconfig other than examining the existing configuration.

ifconfig Sample Output

In Table 307, I have provided a sample output of the “ifconfig -a” command on one of the UNIX machines I use regularly, showing the settings for its interfaces.

Table 307: Sample Routing Table Display From Windows netstat Utility

%ifconfig -a
address: 00:a0:c9:8c:f4:a1
media: Ethernet autoselect (100baseTX full-duplex)
status: active
inet netmask 0xffffffe0 broadcast
inet alias netmask 0xffffffff broadcast
lo0: flags=8009<UP,LOOPBACK,MULTICAST> mtu 33228
inet netmask 0xff000000

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