ISDN Dial-On-Demand: Can't Stop dial with arp packets...

ISDN Dial-On-Demand: Can't Stop dial with arp packets...

Post by Jim Valavani » Thu, 30 Oct 1997 04:00:00



Hello again everybody,

I have installed linux 2.0.30 (Slackware 3.3) on a machine located
remotely from my office connected with ISDN dial-on-demand modem.   I
have diagnosed the dial-out of this machine with TCPDUMP to see why the
machine is dialing out for no reason every 6 minutes or so.

This is the packet that is received from tcp dump from remote host
(durham).

15:28:08.980232 arp who-has ryno.cit-llc.com tell durham.cit-llc.com

ryno is another linux machine on my LAN and durham is the machine on the
remote end that I would like to prevent from dialing out when this
happens.

Now, I ran into a similar problem in a previous version of linux and
modified the /usr/src/linux/net/ipv4/arp.c file and recompiling and
restarting the new kernel.  This has not worked yet as I have tried
different values for the ARP_TIMEOUT and other variables in that file.

Not sure how I can prevent this dial-out from the remote machine.
In case it matters the ISDN boxes that I use are from COMBINET now owned
by Cisco.  Maybe I can filter ARP packets from the ISDN modem?

All help is greatly appreciated.  (I need to save money on this phone
bill).

TIA

Jim Valavanis

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1. Spppcontrol isdn dial-on-demand won't work

I have set up a 4.7 box with a Fritz!PCI 2.0 to use as a gateway. Dial-up
and NAT works fine (meanwhile). But the box won't dial-on-demand when a
client sends a request, neither would it drop the line after the idle-time
set in isdnd.rc (in my case I have set it to 90 seconds for testing)...

This is my rc.local (which seems to work fine, the system is connected when
booted):

# Bring ISDN interface up and connect to ISP
ifconfig isp0 delete -link1 down
echo -n 'Configuring ISP0 to AON Complete:'
echo -n ' spppcontrol';
spppcontrol isp0 myauthname="xxx" myauthproto=pap myauthsecret="xxx"
disable-vj disable-ipv6
echo -n 'up';
ifconfig isp0 0.0.0.0 0.0.0.1 link1 up
echo '.'
route add default -interface isp0
/usr/sbin/sendmail -bd -q30m

Following are the two scripts I currently use to dial resp. drop the line
again:

# ISDN-UP
ifconfig isp0 delete -link1 down
echo -n 'Configuring ISP0 to AON Complete:'
echo -n ' spppcontrol';
spppcontrol isp0 myauthname="xxx" myauthproto=pap myauthsecret="xxx"
disable-vj disable-ipv6
echo -n 'up';
ifconfig isp0 0.0.0.0 0.0.0.1 link1 up
echo '.'
route add default -interface isp0

# ISDN-DOWN
ifconfig isp0 delete -link1 down
ifconfig isp0 link1 up

After bringing the line down with the last script and trying to call a web
page on one of the clients in the LAN nothing would happen, spppcontrol
won't establish a connection.

Any advise?

Thanks
Dominik

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