[Linux] PPP

http://www.faqs.org/docs/Linux-HOWTO/PPP-HOWTO.html#AEN1219
How to Setup a Linux Firewall with PPPoE/NAT/iptables
http://axion.physics.ubc.ca/ppp-linux.html#PPPOptions
http://pptpclient.sourceforge.net/howto-diagnosis.phtml
http://www.yolinux.com/TUTORIALS/LinuxTutorialPPP.html
http://www.linux.org.tw/CLDP/OLD/PPP-HOWTO.html