[lug] ppp and eth0

Gary Hodges Gary.Hodges at noaa.gov
Wed Apr 28 10:55:21 MDT 2004

rm at fabula.de wrote:

>On Wed, Apr 28, 2004 at 09:28:54AM -0600, Gary Hodges wrote:
>>Do I need to bring eth0 down when making a ppp connection?  I've had a 
>>student working on a task for me and he believes that eth0 needs to be 
>>brought down before the ppp connection is established.  This doesn't 
>>make sense to me, but it wouldn't be the first time he proved me wrong.
That would be "Gary," but Gray sounds like a decent nickname....

>>I might be able to help more if you can provide a bit more information.

Thanks for the offer.  My configuration is an isolated machine connected 
to an instrument with CAT5 cable, and a modem on /dev/ttyS1 with ppp 
used to connect to the internet when needed.

eth0:  (PC: -> (Instrument:
ppp: Dials an ISP (NIST) to connect to the internet to upload data, set 
time, etc.

I have to confess an almost total lack of knowledge with Linux and PPP.  
I've let another person deal with this totally and I'm now just sticking 
my nose in because some things don't make sense.  My problem is that 
when PPP is active, I don't get data through eth0.  Also, if I fail to 
connect with PPP than I'm left with no connection to my instrument.  I 
actually just commented out the portions of the scripts that bring eth0 
down and it seemed to work, so maybe I'm fine now.

  Of course, I ship this computer to Mississippi tomorrow so everything 
has to be bullet proof today. :-)  I'd like to have the simplest scripts 
to accomplish the task.

The current scripts with my latest comments:
gwn-tsi:/home/tsi# more /etc/ppp/ppp-on
#/sbin/ifconfig eth0 down
cp /etc/ppp/options.bak /etc/ppp/options
exec /usr/sbin/pppd /dev/ttyS1  57600
gwn-tsi:/home/tsi# more /etc/ppp/ppp-off
# If the ppp0 pid file is present then the program is running. Stop it.
if [ -r /var/run/$DEVICE.pid ]; then
    kill -INT `head -1 /var/run/$DEVICE.pid`
# If the kill did not work then there is no process running for this
# pid. It may also mean that the lock file will be left. You may wish
# to delete the lock file at the same time.
         if [ ! "$?" = "0" ]; then
             rm -f /var/run/$DEVICE.pid
             echo "ERROR: Removed stale pid file"
             exit 1
# Success. Let pppd clean up its own junk.
echo "PPP link to $DEVICE terminated."
/sbin/route delete default
mv /etc/ppp/options /etc/ppp/options.bak
#/sbin/ifconfig eth0 up
#/sbin/route add -net netmask dev lo
#/sbin/route add default gw

exit 0
# The PPP process is not running for ppp0
echo "ERROR: PPP link is not active on $DEVICE"
exit 1

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