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Troubleshooting PPTP Connections

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When troubleshooting a PPTP VPN connection it is always a good idea to watch  /var/log/daemon.log for information. 
Log messages for a successful operations will look like this:

• successful PPTP server startup:

  Nov 25 18:42:49 gw pptpd[28892]: MGR: Maximum of 100 connections reduced to 11, not enough IP addresses
  ... given
  Nov 25 18:42:49 gw pptpd[28893]: MGR: Manager process started
  Nov 25 18:42:49 gw pptpd[28893]: MGR: Maximum of 11 connections available

   

• successful client connection:

  Dec  5 19:10:13 gw pptpd[30721]: CTRL: Client 192.168.1.225 control connection started
  Dec  5 19:10:13 gw pptpd[30721]: CTRL: Starting call (launching pppd, opening GRE)
  Dec  5 19:10:13 gw pppd[30722]: pppd 2.4.4 started by root, uid 0
  Dec  5 19:10:13 gw pppd[30722]: Using interface ppp0
  Dec  5 19:10:13 gw pppd[30722]: Connect: ppp0 <--> /dev/pts/3
  Dec  5 19:10:16 gw pppd[30722]: MPPE 128-bit stateless compression enabled
  Dec  5 19:10:16 gw pppd[30722]: not replacing existing default route via 213.157.174.129
  Dec  5 19:10:16 gw pppd[30722]: Cannot determine ethernet address for proxy ARP
  Dec  5 19:10:16 gw pppd[30722]: local  IP address 172.17.13.1
  Dec  5 19:10:16 gw pppd[30722]: remote IP address 172.17.13.2
  Dec  5 19:11:48 gw pppd[30722]: LCP terminated by peer (MPPE disabled)
  Dec  5 19:11:48 gw pppd[30722]: Connect time 1.6 minutes.
  Dec  5 19:11:48 gw pppd[30722]: Sent 0 bytes, received 3184 bytes.
  Dec  5 19:11:48 gw pptpd[30721]: CTRL: EOF or bad error reading ctrl packet length.
  Dec  5 19:11:48 gw pptpd[30721]: CTRL: couldn't read packet header (exit)
  Dec  5 19:11:48 gw pptpd[30721]: CTRL: CTRL read failed
  Dec  5 19:11:48 gw pptpd[30721]: CTRL: Reaping child PPP[30722]
  Dec  5 19:11:48 gw pppd[30722]: Modem hangup
  Dec  5 19:11:48 gw pppd[30722]: Connection terminated.
  Dec  5 19:11:48 gw pppd[30722]: Exit.
  Dec  5 19:11:48 gw pptpd[30721]: CTRL: Client 192.168.1.225 control connection finished

 

Log messages for errors will look like this:

• invalid username or password for a certain connection:

  Nov 25 18:56:11 gw pptpd[17817]: CTRL: Client 192.168.1.122 control connection started
  Nov 25 18:56:11 gw pptpd[17817]: CTRL: Starting call (launching pppd, opening GRE)
  Nov 25 18:56:11 gw pppd[17818]: pppd 2.4.4 started by root, uid 0
  Nov 25 18:56:11 gw pppd[17818]: Using interface ppp0
  Nov 25 18:56:11 gw pppd[17818]: Connect: ppp0 <--> /dev/pts/2
  Nov 25 18:56:14 gw pppd[17818]: Warning - secret file /etc/ppp/chap-secrets has world and/or group
    ... access
  Nov 25 18:56:14 gw pppd[17818]: Peer dan failed CHAP authentication
  Nov 25 18:56:14 gw pppd[17818]: Connection terminated.
  Nov 25 18:56:14 gw pppd[17818]: Exit.

   

• GRE protocol filtered by other routers or firewalls:

  Nov 25 18:56:14 gw pptpd[17817]: GRE: read(fd=9,buffer=804fa40,len=8196) from PTY failed: status = -1
    ... error = Input/output error, usually caused by unexpected termination of pppd, check option syntax
    ... and pppd logs
  Nov 25 18:56:14 gw pptpd[17817]: CTRL: PTY read or GRE write failed (pty,gre)=(9,10)
  Nov 25 18:56:14 gw pptpd[17817]: CTRL: Reaping child PPP[17818]