I am a network engineer having quite limited experience with Ubuntu. I have been following up these online instructions to set up a pptp server but without much luck to get it to work. My server is a vm running an Apple Xserve behind a Cisco firewall. I made sure tcp 1723 and GRE are opened for the box. Below is the syslog output, looks like I always got stuck at GRE: Bad checksum from pppd. I'm running Ubuntu 10.04. Sep 24 13:21:53 ubuntu pptpd[1231]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7) Sep 24 13:21:53 ubuntu pptpd[1231]: CTRL: Reaping child PPP[1232] Sep 24 13:21:53 ubuntu pptpd[1231]: CTRL: Client 166.137.85.165 control connection finished Sep 24 13:22:41 ubuntu pptpd[1276]: MGR: connections limit (100) reached, extra IP addresses ignored Sep 24 13:22:41 ubuntu pptpd[1277]: MGR: Manager process started Sep 24 13:22:41 ubuntu pptpd[1277]: MGR: Maximum of 100 connections available Sep 24 13:22:50 ubuntu pptpd[1278]: CTRL: Client 166.137.85.165 control connection started Sep 24 13:22:51 ubuntu pptpd[1278]: CTRL: Starting call (launching pppd, opening GRE) Sep 24 13:22:51 ubuntu pppd[1279]: Plugin /usr/lib/pptpd/pptpd-logwtmp.so loaded. Sep 24 13:22:51 ubuntu pppd[1279]: pppd 2.4.5 started by root, uid 0 Sep 24 13:22:51 ubuntu pppd[1279]: Using interface ppp0 Sep 24 13:22:51 ubuntu pppd[1279]: Connect: ppp0 <--> /dev/pts/1 Sep 24 13:22:51 ubuntu pptpd[1278]: GRE: Bad checksum from pppd. Sep 24 13:23:21 ubuntu pppd[1279]: LCP: timeout sending Config-Requests Sep 24 13:23:21 ubuntu pppd[1279]: Connection terminated. Sep 24 13:23:21 ubuntu pppd[1279]: Modem hangup Sep 24 13:23:21 ubuntu pppd[1279]: Exit. Sep 24 13:23:21 ubuntu pptpd[1278]: GRE: read(fd=6,buffer=805a540,len=8196) from PTY failed: status = -1 error = Input/output error, usually caused by unexpected termination of pppd, check option syntax and pppd logs Sep 24 13:23:21 ubuntu pptpd[1278]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7) Sep 24 13:23:21 ubuntu pptpd[1278]: CTRL: Reaping child PPP[1279] Sep 24 13:23:21 ubuntu pptpd[1278]: CTRL: Client 166.137.85.165 control connection finished