Internet Addresses
Addresses
TCP/IP Protocols |
Packets of Information |
Addresses |
The Naming System |
Finding Addresses |
Going Futher
The address on a normal letter typically has several lines,
each of which supplies different levels of information about
the exact location corresponding to the address. In a very
similar way, addresses for Internet information packets
have four fields that contain numbers and are separated
by periods. For example,
160.36.28.37
is an IP address. However, people generally can remember
names better than numbers, so it is convenient to associate
a name with such an IP address. In this case, the corresponding
name is
csep10.phys.utk.edu.
The translation between the numbers used by the network,
and the name more commonly used by people is done by a computer
called a nameserver. The purpose of a nameserver is to look
up addresses, so its function may be likened to directory
assistance on the telephone system.
If I specify csep10.phys.utk.edu as an IP address to a
network, the first thing that it does is call its "directory
assistance" - that is, a nameserver - to get the number
associated with that name. (Actually, most computers have
a small list of address-name mappings stored locally that
they first consult, and only go to an external nameserver
if they don't find the address there.) The network uses
only the number, but by this method the humans and the computers
are both kept happy: the computers in the network just have
to deal with the numbers, which is what they do best, and
the humans using the computers need only remember more symbolic
names like
mycomputer.myplace.mynet.mycountry.
which is what humans do better. Of course, the humans can
also supply the IP address directly to the network as a
number. Then, the nameserver isn't invoked. In fact, sometimes
the nameservers, since they are machines, are down for some
reason and one MUST supply the number to the network. However,
that doesn't happen too often these days on modern and well
maintained networks because there usually is more than one
nameserver available, and if one is down another can often
be found by the network when it needs a name translated.
|