To hide the diversity of equipment that may be used in a networking
environment, TCP/IP defines an abstract interface
through which the hardware is accessed. This interface offers a set of
operations that is the same for all types of hardware and basically deals
with sending and receiving packets.
For each peripheral networking device, a corresponding interface has
to be present in the kernel. For example, Ethernet interfaces in Linux
are called by such names as eth0 and
eth1; PPP (discussed in Chapter 8 ) interfaces are named ppp0
and ppp1; and FDDI interfaces are given names
like fddi0 and fddi1. These
interface names are used for configuration purposes when you want to
specify a particular physical device in a configuration command, and
they have no meaning beyond this use.
Before being used by TCP/IP networking, an interface must be assigned
an IP address that serves as its identification when communicating
with the rest of the world. This address is different from the
interface name mentioned previously; if you compare an interface to a
door, the address is like the nameplate pinned on it.
Other device parameters may be set, like the maximum size of datagrams
that can be processed by a particular piece of hardware, which is referred
to as Maximum Transfer Unit (MTU). Other attributes
will be introduced later. Fortunately, most attributes have sensible defaults.