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config ppp bidirectionally via modem

Posted on 2007-03-19
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Last Modified: 2010-03-18
Here is a blast from the past, comms over serial modems

I need to setup 2 fedora core 5 machines such that a connection can be initiated at either end via these modems. I would prefer to explicitly start & stop the connection process myself rather than rely upon ppp etc to automatically set them up and close them down.

The connection will need to allow command-line login and also ftp in one direction.

I can handle the ftp conversation once the connection between the machines is made.
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Question by:NickUpson
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by:Nopius
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1) Setup PPP server on each Linux with PAP authentication.

2) Suppose your modem is here: "/dev/modem" -> "/dev/ttyS1"

3) Install required packages
yum install mgetty
yum install ppp

4) edit /etc/inittab:
S1:2345:respawn:/sbin/mgetty -D ttyS1

5) edit /etc/mgetty+sendfax/login.config:
/AutoPPP/ - a_ppp /usr/sbin/pppd auth -chap +pap login debug

6) edit /etc/ppp/pap-secrets:
# client server secret IP addresss
* remote "secret" *
remote * "secret" *

7) edit /etc/ppp/options:
lock
-detach
modem
crtscts
asyncmap 0
#proxyarp

8) Edit /etc/ppp/options.ttyS1 with IP addresses localip:remoteip like:
192.168.1.1:192.168.1.2

9) Running PPP client on each Linux should look like here:
pppd connect 'chat "" "ATZ" "" ATDT555-1800 CONNECT ""'  /dev/ttyS1 115200 modem noauth user remote


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by:NickUpson
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where do I put the modem setup, (phone no, etc)
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by:Nopius
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Phone number is setup in 9) in client connection script. In my example it's 555-1800
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by:NickUpson
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Can I avoid the pap authentication & just have security from the login id/password. I'm trying to make this a simple as possible and involve as few changes to the default system as possible
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by:Nopius
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Nick. To avoid any PPP authentication change in
5)
/AutoPPP/ - a_ppp /usr/sbin/pppd noauth -chap -pap debug
7) add
noauth
9) remove these 3 parameters "noauth user remote"
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by:NickUpson
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I assume 6) is no longer required

I seem to remember problems trying to dial out on a port that has getty enabled
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by:Nopius
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May be you are right. Probably getty uses tty lock file while talking to modem port. I'm not sure is lock created while answering dial-in request or on start of getty.
To try out if it's possible to use the same tty, install minicom and try connect to your modem manually while getty is running.
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Nopius earned 500 total points
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Also I remember one recommendation to use different devices for dial-in and dial-out (cua0 against ttyS0). You may also try it if you have lock problems.
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