PPP connection via mac or win modem dialup to dedicated Linux ppp server

PPP connection via mac or win modem dialup to dedicated Linux ppp server

Post by David DeMel » Mon, 27 Apr 1998 04:00:00


I'm running a Caldera OpenLinux installation with kernel 2.0.29.

I'm having problems setting up the Linux box as a ppp server. I've read
all of the other posts here from those with similar problems and also the
PPP-HOWTO and the SERIAL-HOWTO, as well as Craig Hunt's TCP/IP Network
Admin. annd Olaf Kirch's Linux NAG. And yes, I've checked out the online
docs at Caldera, but I think there is something basic that's eluding me
and hope someone can help.

I'm trying to set the machine up as a limited ppp server (one modem/port)
so that I can dial in with a mac or windows laptop using those OS's ppp
implementations to get full TCP/IP access to the internet. I can't find
any discussion of this anywhere - all talk is about linking Linux to

Using mgetty, I've successfully set up dialin access and can connect from
the laptop and use the shell account.

When I try to use MacPPP, for example, and issue the command

      'exec /usr/src/pppd -detach'

ppp launches successfully and I can communicate via TCP/IP between the Mac
and the Linux box (Eudora, Anarchie, Netscape, etc.).

But I can't get past the linux box to the rest of the world.

I have compiled the kernel with IP Forwarding enabled.

I'm giving the laptop an IP in the same subnet as the Linux box
(, which may be a problem (I don't know).

I don't understand how to get the laptop to see the Linux box as a
gateway. Am I even on the right track in trying to do that? I have tried
adding routes manually on the Linux side, but nothing I've tried has

Thanks in advance for taking a second to look at the following, and if you
can point me in the right direction I'd really appreciate it.

This is a picture of what's going on:
                  <GATEWAY FOR MY SUBNET>         (
                  <eth0 OF MY LINUX BOX>          (
                          |   |
                  <ppp0 OF MY LINUX BOX>          (

My /etc/ppp/options looks like this:
asyncmap 0

And I've also tried one that looks like this:
asyncmap 0

Regardless of which one I use, the results of 'netstat -nr' while the ppp
connection is active always look like this:
# netstat -nr
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface UH     1500 0          0 ppp0 U      1500 0          0 eth0       U      3584 0          0 lo         UG     1500 0          0 eth0

David DeMello


1. LINUX<(nullmodem)>Mac PPP connection; LINUX as PPP-server


We are trying to run PPP thru a NULL-MODEM connection between
  -PC running LINUX (running kernel ver. 2.0.0, PPP ver. 2.2.0)
    and a
  -Macintosh running FreePPP ver. 2.5 and apple TCP/IP 1.1

Of course, we want LINUX to be the PPP-server and the Mac to be
the client.

This is how far we get:

   as root, we run:

   /usr/sbin/pppd -detach modem crtscts lock : /dev/ttyS1

   In the terminal window FreePPP recognises the ppp-startup string
   sent by linux. The local IP is also set.
   Anyway, all seems to go well. FreePPP says:
      -establishing communicatiom
      -established communication
      -(short time passes)
      -link dead
      -connection was established but it is not a reliable connection
       was terminated.

meanwhile at LINUX:
/var/adm/messages reads:
Sep 29 17:18:34 zorn pppd[147]: pppd 2.2.0 started by root, uid 0
Sep 29 17:18:58 zorn pppd[147]: Serial connection established.
Sep 29 17:18:59 zorn pppd[147]: Using interface ppp0
Sep 29 17:18:59 zorn pppd[147]: Connect: ppp0 <--> /dev/ttyS1
Sep 29 17:19:01 zorn pppd[147]: local  IP address
Sep 29 17:19:01 zorn pppd[147]: remote IP address

We have the feeling we are quite close to succes... :-}
Can anybody help us out?

Thanks in advance!

Maarten and David

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