Updated: April 19, 2023 |
The following script starts the Point-to-Point Protocol daemon, pppd, with a chat script, waits for the modem to ring, answers it, and starts PPP services with CHAP (Challenge-Handshake Authentication Protocol) authentication. After PPP services have terminated, or an error on modem answer occurs, it restarts and waits for the next call.
#!/bin/sh SERIAL_PORT=$1 DEFAULT_SERIAL_PORT=/dev/ser1 PPPD="/usr/sbin/pppd" DO_CHAT="chat -v ABORT BUSY ABORT CARRIER ABORT ERROR \ TIMEOUT 32000000 RING ATA TIMEOUT 60 CONNECT \d\d\d" STTY="/bin/stty" ECHO="/bin/echo" LOCAL_IP=10.99.99.1 REMOTE_IP=10.99.99.2 if [ "$SERIAL_PORT" == "" ]; then SERIAL_PORT=$DEFAULT_SERIAL_PORT fi #do some initialization $STTY +sane +raw < $SERIAL_PORT while [ true ]; do $ECHO "Waiting on modem $SERIAL_PORT..." $ECHO "Starting PPP services..." $PPPD connect "$DO_CHAT" debug nodetach auth +chap \ $LOCAL_IP:$REMOTE_IP $SERIAL_PORT done;
The TIMEOUT is 32000000 because it's a long period of time before the timeout takes effect; chat doesn't allow an infinite wait. The /etc/ppp/chap-secrets is as follows:
# Client Server Secret Addresses allowed ############################################################## * * "password" *
You can also extend the chat script that answers the modem to be a little more robust with specific events that should restart the answering service other than the events given. You might want to add other features as well.
Here's the buildfile used to set up a machine to allow telnet connections (to log in for shell access) and tftp access (for file transfer) over PPP:
[virtual=x86_64,bios +compress] .bootstrap = { startup-x86 -K8250.2f8^0.57600.1843200.16 -v PATH=/proc/boot procnto-smp-instr -vvv } [+script] startup-script = { pci-server & waitfor /dev/pci # Start 1 keyboard console devc-con -n8 & # Start serial A driver waitfor /dev/con1 reopen /dev/con1 devc-ser8250 -e -b38400 waitfor /dev/ser1 pipe touch /tmp/syslog syslogd devc-pty io-pkt-v4-hc -pabc100 if_up -p abc0 inetd & display_msg "[Shell]" [+session] PATH=/bin:/proc/boot /bin/sh & } # Make /tmp point to the shared memory area... [type=link] /tmp=/dev/shmem [type=link] /bin/sh=/bin/ksh # We use the "C" shared lib libc.so libgcc_s.so.1 /usr/lib/ldqnx-64.so.2=ldqnx-64.so.2 libsocket.so devc-con devc-ser8250 devc-pty pci-server pipe io-pkt-v4-hc /bin/echo=echo /bin/stty=stty tail pci chat ifconfig ping syslogd touch ./modem_ans_ppp.sh #Services (telnetd etc) config inetd /usr/sbin/telnetd=telnetd /usr/sbin/tftpd=tftpd /usr/sbin/pppd=pppd /bin/login=login /bin/ksh=ksh /etc/ppp/chap-secrets = { # Client Server Secret Addrs ######################################### * * "password" * } /etc/syslog.conf = { *.* /tmp/syslog } # Inetd config Files /etc/services= /etc/services /etc/protocols= /etc/protocols /etc/termcap= /etc/termcap /etc/passwd= /etc/passwd /etc/default/login= /etc/default/login /etc/resolv.conf= /etc/resolv.conf /etc/nsswitch.conf= /etc/nsswitch.conf /etc/shadow = /etc/shadow /etc/inetd.conf = { telnet stream tcp nowait root /usr/sbin/telnetd in.telnetd tftp dgram udp wait root /usr/sbin/tftpd in.tftpd } /etc/hosts = { 127.1 localhost.localdomain localhost 10.99.99.1 server server 10.99.99.2 client client }
Using two computers with modems, you can have one automatically answer, establish PPP services, and authenticate. You can then telnet and tftp to the server from a client. Use these client pppd parameters (in addition to the same chap-secrets file):
pppd connect "chat -v -f/tmp/dial_modem" auth +chap /dev/ser3
but use the appropriate serial port for the client-side modem instead of /dev/ser3. Make sure you use the full path to your modem script. The chat script, dial_modem, is fairly simple:
ABORT 'NO CARRIER' ABORT 'ERROR' ABORT 'BUSY' '' ATDTxxxxxxx CONNECT ''