tlug: PPP for Dummies :-)

[Karl-Max Wagner <karlmax@example.com>]

Hi everybody,

as there apparently are people having trouble with getting ppp
running ( wonder why.....it's that easy..... ) I'll give some
instruction of doing it the quick and dirty and easy way.

First, the basis for checking any modem connection is a terminal
program. Minicom is simple and handy.

Start up Minicom and see to it that it is started on the serial
port your modem is connected to. See to it that the modem is
initialized correctly. Test that by dialling into an ordinary
BBS system and see whether everything works correctly. Try a
zmodem download, if possible to verify whether that works.

Everything OK ? Good. Now we will proceed to getting a ppp
connection to your Internet provider. Before we proceed any
further, we will deal with the theory of authentication first.

There are two fundamental ways of authentication: terminal and
pap/chap authentication. Terminal authentication is just what it
says: you get a "login:" prompt, reply with your login name,
then you get a "Password:" prompt and you reply with your
password. Then you are logged in. If you did that with your
ISP, you won't get a shell prompt now. After a few seconds
you'll see garbage like this: #$%&'()~+* This is actually the
ppp daemon of your ISP trying to talk to its colleague of your
machine.

In case you have pap/chap authentication you just wait for your
modem to get the connection to your ISP. Then you leave your
terminal program WITHOUT CLOSING DOWN THE CONNECTION and start
your ppp in authentication mode. Your pppd now talks to that one
of the ISP and does the authentication for you and then sets up
the ppp connection. Nifty, eh ?

In the case of Minicom you do that by typing the sequence CTRL-A Q
and then starting up your pppd with the required parameters.

Good, you say, and what are the required parameters ? Here is
what I use for terminal authentication:

/usr/sbin/pppd /dev/ttyS1 57600 crtscts mtu 1500 mru 1500 \
defaultroute noipdefault

What does that mean ? Glad ya asked :-)

In the above pppd is started using its absolute address (a
little bit of luxury maybe....). It is connected to the
interface /dev/ttyS1, in other words, COM2 (to use DOS lingo)
with a speed of 57600 bits/second. On the serial interface
hardware flow control is used using the RTS/CTS status lines (
this is what "crtscts" means ). The maximum packet sizes for
transmission (mtu) and reception (mru) are 1500 bytes ( this is
what "mtu 1500 mru 1500" mean ). Then follows a "\" which simply
escapes the linefeed at the end of the line to append the stuff
of the next line, too.

What the fuch then means "defaultroute noipdefault".
Hahaaa....that's the net wizard's special incantations.....

A "defaultroute" has to do with Internet routing. It is the
interface to which all requests for addresses locally unknown
are sent. Locally unknown means, if the addresses or the network
to which they belong are not explicitely entered into your
kernel routing table ( to read it type "route" at the command
prompt ). And now the important catch......

It may happen that you configured your scripts in a way that the
defaultroute is already set to your ethernet card interface if
you have one. In this case your kernel sends all requests to
your ethernet interface instead to the ppp interface and from
there into the Internet. 

So what have you got then ? Your PPP connection runs fine, but
all your requests to the Internet go into the Bg Bit Bucket.

Ultra super uncool megabummer !!!! No Internet !

So, when doing a "route" and the default does not point to
ppp something you got that problem. Go and change the startup
scripts involved. Then reboot and start up ppp again. If route
now shows the correct default route you're all set. Go and enjoy
the Internet.....

Now for the remaining incantation that reads "noipdefault". Most
probably you don't have a fixed IP address, your ISP assigns you
one each time you dial in. This "noipdefault makes pppd ask for
the assignment of an IP address from the ISP and subsequently
using it for the connection. Just leave it there. It always
works :-)

More catches......
It is of utmost importance that the speed and the interface you
connect to using Minicom and subsequently pppd are EXACTLY the
same for both or your pppd will die after a few seconds. So if
you connect to /dev/modem under Minicom you also have to connect
to /dev/modem with pppd. /dev/cua1 or /dev/ttyS1 WON'T do, even
when /dev/modem is a link to one of them.

Also see to it that the protocol under Minicom is set to "8n1"
(8 data bits, no parity, one stop bit).

OK.....and how about that pap/chap stuff ? Well, just a little
extension......

Here is my callup of pppd for pap:

/usr/sbin/pppd /dev/ttyS1 57600 crtscts mtu 1500 mru 1500 \
defaultroute noipdefault remotename oberland.net user karlmax

As you can see, it's exactly the same garbage than above with
some stuff added, more specifically "remotename oberland.net
user karlmax". The remotename is simply the name of my ISP (the
best in the world - you should subscribe to them, too) and my
username there.

Actually, the remotename is only required to find the correct
line in the file containing the password, /etc/ppp/pap-secrets.

In my case it looks like this:

karlmax   oberland.net   MyPassword

It may have more than one line, but I need only one. The
sequence of entries in a line is <username> <remotename>
<password>.

Hey, and don't try to pirate my account with the above. I have
another password, of course.....

As already said in the above, you just use Minicom to get a
modem connection running and then leave it and start up pppd to
do the rest. I put all that into little scripts calling up
minicom first and automatically launching pppd when I leave
minicom.

And by the way, there is a good book on Linux networking: Olaf
Kirch's "Linux Network administrator's Guide". The book is
excellent and helped me a lot when I started. It is available
from O'Reilly in paper form or from any good LDP archive in
electronic form. Get it and study it.

Hello, TLUG archivar ! Please could you put this posting into
some sort of archive, into the TLUG homepage or whatever ? I
have that eerie feeling that the next newbie will ask the same
questions soon and I don't want to post that every week ! Thank
you !

Hope that helps. Questions welcome !

                                Karl-Max Wagner
                                karlmax@example.com
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