[pptp-server] LCP: timeout sending Config-Request

[Vlad Strezhnev]

We have a problem connecting to PopToP server through a firewall.
(Direct connection works OK)
It appears that our firewall lets packets through but then the 
connection fails with timeout.
Following is a log of a sample session.
Highlighted is the relevant line.
Could anybody give a hint on where we should look first for 
misconfiguration?

#Start of the log ###############

Sep 14 19:00:42 [hosthame] pptpd[2586]: CTRL: Client [ip address] 
control connection started
Sep 14 19:00:42 [hosthame] pptpd[2586]: CTRL: Starting call 
(launching pppd, opening GRE)
Sep 14 19:00:42 [hosthame] kernel: CSLIP: code copyright 1989 Regents 
of the University of California 
Sep 14 19:00:42 [hosthame] kernel: PPP: version 2.3.11 (demand 
dialling) 
Sep 14 19:00:42 [hosthame] kernel: PPP line discipline registered. 
Sep 14 19:00:42 [hosthame] kernel: registered device ppp0 
Sep 14 19:00:42 [hosthame] pppd[2587]: pppd 2.3.11 started by root, 
uid 0
Sep 14 19:00:42 [hosthame] pppd[2587]: Using interface ppp0
Sep 14 19:00:42 [hosthame] pppd[2587]: Connect: ppp0 <--> /dev/pts/1
Sep 14 19:00:42 [hosthame] pptpd[2586]: GRE: Discarding duplicate 
packet
Sep 14 19:01:12 [hosthame] last message repeated 27 times
##################################################################
Sep 14 19:01:12 [hosthame] pppd[2587]: LCP: timeout sending Config-
Requests 
##################################################################
Sep 14 19:01:12 [hosthame] pppd[2587]: Connection terminated.
Sep 14 19:01:12 [hosthame] pppd[2587]: Exit.
Sep 14 19:01:12 [hosthame] pptpd[2586]: GRE: 
read(fd=4,buffer=12010667c,len=8196) \
	from PTY failed: status = -1 error = Input/output error
Sep 14 19:01:12 [hosthame] pptpd[2586]: CTRL: PTY read or GRE write 
failed (pty,gre)=(4,5)
Sep 14 19:01:12 [hosthame] pptpd[2586]: CTRL: Client [ip address] 
control connection finished