Modems and PPP on Linux

First, watch out for those pesky WinModems!

Enabling dialin PPP access to a Linux server takes several small steps which are easy to forget, so here they are in one handy list.

• Set up the modem and check that you can dial out using minicom.
• Install mgetty and write its config file (typically /etc/mgetty+sendfax/mgetty.config), kind of like this one:

  debug 1
  fax-id +001-999-555-1212
  port ttyS2
    speed 57600
    rings 8
    modem-type c2.0
  

• Also configure /etc/mgetty+sendfax/login.config by enabling the line

  /AutoPPP/ -     a_ppp   /usr/sbin/pppd auth -chap +pap login debug
  

• Add the following lines to /etc/ppp/pap-secrets to allow everyone except root to use the dialin line.

  *       *       ""      *
  root    *       -       -
  

• Configure /etc/ppp/options as follows, where aa.bb.cc.dd is the address you want the server to assign to the calling client. Choose aa.bb.cc.dd to be on the same subnet as the server. pp.qq.rr.ss is the IP address of the DNS and WINS providers on the server's network.

  ttyS2 modem 38400 crtscts lock nodetach
  :aa.bb.cc.dd ktune proxyarp
  ms-dns pp.qq.rr.ss ms-wins pp.qq.rr.ss