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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
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2 Answers 2

Personally I am unfamiliar with this. But I like to go out of my way to help.

There were users experiencing the same issue as yourself and have fixed it. Here is the related ubuntuforums post for a possible fix: Ubuntu Forums

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Try opening a webpage. Does it take longer than it normally would? You might receive invalid answers because of a slow Internet connection. If that is the case, try getting a better connection. Plug into Ethernet if you haven't already.

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