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AFRIK-IT  April 1998

AFRIK-IT April 1998

Subject:

Re: Defining the Internet (long)

From:

Dr Eberhard W Lisse <[log in to unmask]>

Reply-To:

[log in to unmask]

Date:

Sat, 11 Apr 1998 20:20:45 +0100

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (108 lines)

Hi

I personally am getting ever more frightened by this or rather where
this is coming from.

In message <[log in to unmask]>, Jeff Cochrane 205 writes:

> > Yes. ALL (as in every) computer (or communicating device) on the Internet
> > has to have an IP address.  There are no exceptions.

> I have a friend in Malawi who has an address something like this:
>
> [log in to unmask]
>
> How do I find out what this friend's IP address is?

He doesn't have an IP address because his communicating device is NOT
on the Internet.

Remember what I wrote about the Matrix?

The Internet is as we discussed before, a network of internets. Each
communicating device on any of those internets has an IP number. The
devices communicate with each other by sending each other packets
which are defined by a protocol. Each packet has the sender's and the
recipient's netwrok address number in it.

It's a layered protocol:

    Ethernet<->IP<->TCP<->SMTP(MTA)/POP(MUA)<->TCP<->IP<->Ethernet
DialUp<->PPP<->IP<->TCP<->SMTP(MTA)/POP(MUA)<->TCP<->IP<->Ethernet

The particular feature of interest of IP is that the communicating
devices decide (routers) where to send the packets, not the sender. If
one adds a new device the routers can "learn" about this and tell
other routers.  If a router goes down, other routes can establish
temselves.

If you dial up to an ISP, using PPP you are given a UNIQUE IP address
temporarily. Your computer is now visible on the Internet.  The TCP
protocol establishes a virtual, error free connection with the target
software. It does not mind about where that software sits, IP does
that part.

Your mail program (MUA) connects to a Mail Transfer Agent (MTA)
usually called sendmail speaking SMTP.  As TCP establishes an error
free virtual connection to the target, the Simple Mail Transfer
Protocol does not need to do any fancy stuff.

To receive mail, your mail program uses the Post Office Protocol to
read your mail file on a server again via TCP also using a very simple
language.

Now how does mail gets sent to [log in to unmask] when eo.wn.apc.org
is not on the Internet?

The MTAs use DNS (Domain Name System) to figure this out.

I don't want to go into too much detail, but basically all systems
that can receive mail (on the Matrix) (should) have at least one DNS
data base entry defining their Mail eXchange host(s).

Let's look at an example:

LISTSERV.HEA.IE.        1h5m43s IN A    193.1.198.5
LISTSERV.HEA.IE.        1h5m43s IN MX   100 LISTSERV.HEA.IE.

AFRIK-IT's list server is on the Internet with the IP number
193.1.198.5 and is its own Mail eXchanger.

eo.wn.apc.org.          1d6h IN MX      10 demiurge.wn.apc.org.
eo.wn.apc.org.          1d6h IN MX      20 wn.apc.org.


EO does not have an IP number but it has two Mail eXchangers. If
DEMIURGE is off line mail goes to WN until it comes back.

Now the beauty of this is that only DEMIURGE needs to know how to
deliver and receive mail to and from EO. (Actually not even that, it
just must forward it somewhere, somehow)

My guess is that in this particular case they use FIDO protocol but it
could be UUCP, DECNET, Appletalk, or Xwhatever.

Now the tools I used to figure out the DNS stuff are part of the most
common DNS server, the Berkely InterNet Daemon (bind).

On a Unix system

        dig listserv.hea.ie any any
        dig eo.wn.apc.org any any

will give the above and some more info. For Macintosh and Windows95
there other tools to be found on simtel and tucows mirrors for example
under the heading DNS.

If more information is needed there are excellent resources on DNS on
the net, the best being HTTP://www.dns.net/dnsrd/

greetings, el
--
Dr. Eberhard W. Lisse\         /              Swakopmund State Hospital
<[log in to unmask]>         *        |               Resident Medical Officer
Private Bag 5004       \      / +264 81 124 6733 (cell) 64 461005(h) 461004(f)
Swakopmund, Namibia     ;____/ Domain Coordinator for NA-DOM (el108)
Vice-Chairman, Board of Trustees, Namibian Internet Development Foundation,
an Association not for Gain. NAMIDEF is the Namibian Internet Service Provider.

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