Maybe that is too simple. A few qualifications:
>>Do all Internet services require the user to have an IP number? When
>>I send an email, for example, does the receiving system need to know
>>my IP number, or simply the IP number of my SMTP server?
> Yes. ALL (as in every) computer (or communicating device) on the Internet
> has to have an IP address. There are no exceptions.
If you are on the inside of a gateway or firewall, your IP-address is irrelevant
to the network. All our users have IP-addresses that would be "illegal " on
the Internet, but it is only our gateway's IP address that is used. Of course it
is valid to state that our users are not on the Internet (we do not offer browsing,
I tend to sympathise with the stethoscope guy especially when it comes to offer
Web browsing on a 9600bps line) but it is possible to offer both e-mail and
browsing w/o each user having a valid Internet IP address.
Note that a e-mail address does not map to an IP-address, it is the server that
maps like that
[log in to unmask]
could be the same as
[log in to unmask]
Where "me" is a user on the server "some.server.com" and that server has the
IP address stated.
In fact you need not have (even an invalid) IP address to use E-mail, since many
mail systems made for e.g. Novell networks, Lotus Notes etc. can work w/o TCP/IP,
and will have a gateway to the Net.
For the home users, they have no fixed IP address, but normally receives
one at the time they log on to their service provider. That way the ISP only
needs to have enough (valid) IP addresses for the number of lines, not as
many as the number of users (normally 1/10 the number for a good ISP).
To browse the Web from inside a Firewall your IP address will not appear in
your packages, only the firewall's IP address. Since there is no WWW browsing
without TCP/IP you would still have a IP address on the inside, but that might be
one already in use on the Internet, nobody would notice.
The techniques of using IP services w/o assigning a IP address for every
single connected device on the Internet is helping us from already having
total IP address starvation.
>[log in to unmask]
You can find the IP address very simple for the server eo.wn.apc.org
(the simples I can think of is to use the "Ping" program), but you can
not find the user's IP address unless you investigate the mail headers
from him and find it there. And even then it is probably a temporary
address as stated above.