ifconfig Command

Purpose

Configures or displays network interface parameters for a network using TCP/IP.

Syntax

ifconfig Interface [ AddressFamily [ Address [ DestinationAddress  ] ] [ Parameters... ] ]

ifconfig Interface [ ProtocolFamily ] Interface ProtocolFamily

ifconfig -a [ -l ] [ -d ] [ -u ] [ ProtocolFamily ]

Description

You can use the ifconfig command to assign an address to a network interface and to configure or display the current network interface configuration information. The ifconfig command must be used at system startup to define the network address of each interface present on a machine. After system startup, it can also be used to redefine an interface's address and its other operating parameters. The network interface configuration is held on the running system and must be reset at each system restart. The ifconfig command interprets the IFF_MULTICAST flag and prints its value if it is set.

An interface can receive transmissions in differing protocols, each of which may require separate naming schemes. It is necessary to specify the AddressFamily parameter, which may change the interpretation of the remaining parameters. The address families currently supported are inet, inet6, and ns.

For the DARPA-Internet family, inet, the address is either a host name present in the hostname database, that is, the /etc/hosts file, or a DARPA-Internet address expressed in the Internet standard dotted decimal notation.

For the Xerox Network Systems (XNS) family, ns, addresses are net:a.b.c.d.e.f., where net is the assigned network number (in decimals), and each of the 6 bytes of the host number, a through f, are specified in hexadecimal. The host number may be omitted on 10-Mbps Ethernet interfaces, which use the hardware physical address, and on interfaces other than the first interface.

While any user can query the status of a network interface, only a user who has administrative authority can modify the configuration of those interfaces.

The ifconfig function 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.

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

Gratuitous ARP is supported for ethernet, token-ring, and FDDI interfaces. This means when an IP address is assigned, the host sends an ARP request for its own address (the new address) to inform other machines of its address so that they can update their ARP entry immediately. It also lets hosts detect duplicate IP address. If you get a response to the ARP request, an error is logged in /var/adm/ras/errlog which can be viewed using errpt command (or using SMIT interface) for the error ID AIXIF_ARP_DUP_ADDR.

Flags

Parameters

ifconfig interface inet6 first address

Examples

The following are examples using the ifconfig command on a TCP/IP network and an XNS network:

Inet Examples

1. To query the status of a serial line IP interface, enter the command in the following format:

   ifconfig  sl1

   In this example, the interface to be queried is sl1. The result of the command looks similar to the following:

   sl1:  flags=51<UP,POINTOPOINT,RUNNING>
               inet  192.9.201.3  -->  192.9.354.7  netmask  ffffff00

2. To configure the local loopback interface, enter the command in the following format:

   ifconfig  lo0  inet  127.0.0.1  up

3. To mark the local Token-Ring interface as down, enter the command in the following format:

   ifconfig  tr0  inet  down

   In this example, the interface to be marked is token0.

   Note: Only a user with root user authority can modify the configuration of a network interface.

4. To turn rfc1323 off for all connections over en5 (assuming that the global value is 1), enter:

   ifconfig en0 rfc1323 0

XNS Examples

1. To configure a Standard Ethernet type interface for XNS, enter the command in the following format:

   ifconfig  en0  ns  110:02.60.8c.2c.a4.98  up

   In this example, ns is the XNS address family, 110 is the network number and 02.60.8c.2c.a4.98 is the host number, which is the Ethernet address unique to each individual interface. Specify the host number when there are multiple Ethernet hardware interfaces, as the default may not correspond to the proper interface. The Ethernet address can be obtained by the commands:

   ifconfig  en0
   netstat  -v

   The XNS address can be represented several ways, as shown in the following examples:

   • 123#9.89.3c.90.45.56
   • 5-124#123-456-900-455-749
   • 0x45:0x9893c9045569:90
   • 0456:9893c9045569H

   The XNS address in the first example is in decimal format. The address in the second example is broken into groups of three digits, with each group separated by a - (minus sign). The 0x and H addresses are in hex format. Finally, the 0 in front of the last address indicates that the number is in octal format.

2. To configure an IEEE Ethernet 802.3 type interface for XNS, enter the command in the following format:

   ifconfig  et0  ns  120:02.60.8c.2c.a4.98  up

   The en0 and et0 interfaces are considered as separate interfaces even though the same Ethernet adapter is used. Two separate networks can be defined and used at the same time as long as they have separate network numbers. Multiple Ethernet adapters are supported.

   Note: The host number should correspond to the Ethernet address on the hardware adapter. A system can have multiple host numbers.

3. To configure an Internet encapsulation XNS interface, enter the command in the following format:

   ifconfig  en0  inet  11.0.0.1  up
   ifconfig  en0  ns  110:02.60.8c.2c.a4.98  up
   ifconfig  en0  ns  130:02.60.8c.34.56.78  ipdst  11.0.0.10

   The first command brings up the Internet with the inet address 11.0.0.1. The second command configures the en0 interface to be network 110 and host number 02.60.8c.2c.a4.98 in the ns address family. This defines the host number for use when the XNS packet is encapsulated within the Internet packet. The last command defines network 130, host number 02.60.8c.34.56.78, and destination Internet address 11.0.0.10. This last entry creates a new network interface, nsip. Use the netstat -i command for information about this interface.

Files

Related Information

The netstat command.

The hosts file format, networks file format.

TCP/IP Network Interfaces, Understanding Protocols, TCP/IP Routing, Subnet Addresses in AIX Version 4.3 System Management Guide: Communications and Networks.

Xerox Network Systems (XNS) Overview for Programming in AIX Version 4.3 General Programming Concepts: Writing and Debugging Programs.