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Quoting from the ifconfig man page:

ifconfig is used to configure the kernel-resident network interfaces. It is used at boot time to set up interfaces as necessary. After that, it is usually only needed when debugging or when system tuning is needed.

What does kernel-resident mean?

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From Serial Line Networking in Linux:

The term Network Interface is used for marking both the interface itself and the whole low-level stuff including HW specific things. The whole low-level communication stuff in LINUX consists basically of two things:

Kernel-Resident Network Interface

Kernel object used by TCP/IP as the Network Interface.
    lo: loopback network interface
    eth0: ethernet network interface
    sl2: SLIP/CSLIP network interface
    ppp0: PPP network interface

Device driver

Driver of your network card or serial port or something else.
Examples: /dev/ttyS0 ...
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So . . . kernel object means the "dev" device? Can the network card ( physical network interface ) be kernel resident without an appropriate driver ( module? ) installed? – chad Sep 25 '12 at 17:42
@chad: Kernel Resident means the in kernel memory data structures. They are used by the device driver to operate the hardware. If you try to configure an interface for which no driver exists it will fail. – bahamat Sep 25 '12 at 18:03
So, the driver creates the "in kernel memory data structures"? – chad Sep 25 '12 at 18:05

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