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IFTAB

Section: Linux Programmer's Manual (5)
Updated: 01 March 2004
Index Return to Main Contents
 

NAME

iftab - static information about the network interfaces  

DESCRIPTION

The file /etc/iftab contains descriptive information about the various network interfaces. iftab is only used by the program ifrename(8) to assign a consistent network interface name to each network interface.

/etc/iftab defines a set of mappings. Each mapping contains an interface name and a set of selectors. The selectors allow ifrename to identify each network interface on the system. If a network interface matches all descriptors of a mapping, ifrename attempt to change the name of the interface to the interface name given by the mapping.  

MAPPINGS

Each mapping is described on a separate line, it starts with an interface name, and contains a set of descriptors, separated by space or tabs.

The relationship between descriptors of a mapping is a logical and. A mapping matches a network interface only is all the descriptors match. If a network interface doesn't support a specific descriptor, it won't match any mappings using this descriptor.

If you want to use alternate descriptors for an interface name (logical or), specify two different mappings with the same interface name (one on each line). Ifrename always use the first matching mapping starting from the end of iftab, therefore more restrictive mapping should be specified last.  

INTERFACE NAME

The first part of each mapping is an interface name. If a network interface matches all descriptors of a mapping, ifrename attempt to change the name of the interface to the interface name given by the mapping.

The interface name of a mapping is either a plain interface name (such as eth2 or wlan1) or a interface name pattern containing a single wildcard (such as eth* or wlan*). In case of wildcard, the kernel replace the '*' with the lowest available integer making this interface name unique. Note that wildcard is only supported for kernel 2.6.1 and 2.4.30 and later.

It is discouraged to try to map interfaces to default interfaces names such as eth0, wlan0 or ppp0. The kernel use those as the default name for any new interface, therefore most likely an interface will already use this name and prevent ifrename to use it. Even if you use takeover, the interface may already be up in some cases. Not using those name will allow you to immediately spot unconfigured or new interfaces.
Good names are either totally unique and meaningfull, such as mydsl or privatehub, or use larger integer, such as eth5 or wlan5. The second type is usually easier to integrate in various network utilities.  

DESCRIPTORS

Each descriptor is composed of a descriptor name and descriptor value. Descriptors specify a static attribute of a network interface, the goal is to uniquely identify each piece of hardware.

Most users will only use the mac selector, other selectors are for more specialised setup.

mac mac address
Matches the MAC Address of the interface with the specified MAC address. The MAC address of the interface can be shown using ifconfig(8) or ip(8). The specified MAC address may contain a '*' for wilcard matching.
This is the most common selector, as most interfaces have a unique MAC address allowing to identify network interfaces without ambiguity. However, some interfaces don't have a valid MAC address until they are brought up, in such case using this selector is tricky.
arp arp type
Matches the ARP Type (also called Link Type) of the interface with the specified ARP type. The ARP Type of the interface can be shown using ifconfig(8) or ip(8).
This selector is useful when a driver create multiple network interfaces for a single network card.
driver driver name
Matches the Driver Name of the interface with the specified driver name. The Driver Name of the interface can be shown using ethtool -i(8).
businfo bus information
Matches the Bus Information of the interface with the specified bus information. The Bus Information of the interface can be shown using ethtool -i(8).
firmware firmware revision
Matches the Firmware Revision of the interface with the firmware revision information. The Firmware Revision of the interface can be shown using ethtool -i(8).
baseaddress base address
Matches the Base Address of the interface with the specified base address. The Base Address of the interface can be shown using ifconfig(8).
Because most cards use dynamic allocation of the Base Address, this selector is only useful for ISA and EISA cards.
irq irq line
Matches the IRQ Line (interrupt) of the interface with the specified IRQ line. The IRQ Line of the interface can be shown using ifconfig(8).
Because there are IRQ Lines may be shared, this selector is usually not sufficient to uniquely identify an interface.
iwproto wireless protocol
Matches the Wireless Protocol of the interface with the specified wireless protocol. The Wireless Protocol of the interface can be shown using iwconfig(8).
This selector is only supported on wireless interfaces and is not sufficient to uniquely identify an interface.
pcmciaslot pcmcia slot
Matches the Pcmcia Socket number of the interface with the specified slot number. Pcmcia Socket number of the interface can be shown using cardctl ident(8).
This selector is usually only supported on 16 bits cards, for 32 bits cards it is advised to use the selector businfo.
SYSFS{filename} value
Matches the sysfs attribute given by filename to the specified value. sysfs attributes of the interface can be read in one of the directory in the directory /sys/class/net/. For example, the filename address is the MAC address of the device and should be identical to the selector mac.
The sysfs filesystem is only supported with 2.6.X kernel and need to be mounted. sysfs selectors are not as efficient as other selectors, therefore they should be avoided for maximum performance.
 

EXAMPLE

# This is a comment
eth2           mac 08:00:09:DE:82:0E

eth3           driver wavelan interrupt 15 baseaddress 0x390

eth4           driver pcnet32 businfo 0000:02:05.0

air*           mac 00:07:0E:* arp 1

myvpn  SYSFS{address} 00:10:83:*
 

AUTHOR

Jean Tourrilhes - jt@hpl.hp.com  

FILES

/etc/iftab  

SEE ALSO

ifrename(8), ifconfig(8), ip(8), ethtool(8), iwconfig(8).


 

Index

NAME
DESCRIPTION
MAPPINGS
INTERFACE NAME
DESCRIPTORS
EXAMPLE
AUTHOR
FILES
SEE ALSO




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