такая вот проблема, в логе:
Apr 23 11:38:20 mx pptpd[26755]: MGR: Launching /usr/sbin/pptpctrl to handle client
Apr 23 11:38:20 mx pptpd[26755]: CTRL: local address = 172.16.0.1
Apr 23 11:38:20 mx pptpd[26755]: CTRL: remote address = 172.16.0.2
Apr 23 11:38:20 mx pptpd[26755]: CTRL: pppd options file = /etc/ppp/pptpd-options
Apr 23 11:38:20 mx pptpd[26755]: CTRL: Client 223.255.253.49 control connection started
Apr 23 11:38:20 mx pptpd[26755]: CTRL: Received PPTP Control Message (type: 1)
Apr 23 11:38:20 mx pptpd[26755]: CTRL: Made a START CTRL CONN RPLY packet
Apr 23 11:38:20 mx pptpd[26755]: CTRL: I wrote 156 bytes to the client.
Apr 23 11:38:20 mx pptpd[26755]: CTRL: Sent packet to client
Apr 23 11:38:20 mx pptpd[26755]: CTRL: Received PPTP Control Message (type: 7)
Apr 23 11:38:20 mx pptpd[26755]: CTRL: Set parameters to 100000000 maxbps, 64 window size
Apr 23 11:38:20 mx pptpd[26755]: CTRL: Made a OUT CALL RPLY packet
Apr 23 11:38:20 mx pptpd[26755]: CTRL: Starting call (launching pppd, opening GRE)
Apr 23 11:38:20 mx pptpd[26755]: CTRL: pty_fd = 9
Apr 23 11:38:20 mx pptpd[26755]: CTRL: tty_fd = 10
Apr 23 11:38:20 mx pptpd[26756]: CTRL (PPPD Launcher): program binary = /usr/sbin/pppd
Apr 23 11:38:20 mx pptpd[26756]: CTRL (PPPD Launcher): local address = 172.16.0.1
Apr 23 11:38:20 mx pptpd[26756]: CTRL (PPPD Launcher): remote address = 172.16.0.2
Apr 23 11:38:20 mx pppd[26756]: Plugin /usr/lib/pptpd/pptpd-logwtmp.so loaded.
Apr 23 11:38:20 mx pppd[26756]: pptpd-logwtmp: $Version$
Apr 23 11:38:20 mx pppd[26756]: The remote system is required to authenticate itself
Apr 23 11:38:20 mx pppd[26756]: but I couldn't find any suitable secret (password) for it to use to do so.
Apr 23 11:38:20 mx pppd[26756]: (None of the available passwords would let it use an IP address.)
Apr 23 11:38:20 mx pptpd[26755]: CTRL: I wrote 32 bytes to the client.
Apr 23 11:38:20 mx pptpd[26755]: CTRL: Sent packet to client
Apr 23 11:38:20 mx pptpd[26755]: GRE: read(fd=9,buffer=8058640,len=8196) from PTY failed: status = -1 error = Input/output error, usually caused by unexpected termination of pppd, check option syntax and pppd logs
Apr 23 11:38:20 mx pptpd[26755]: CTRL: PTY read or GRE write failed (pty,gre)=(9,10)
Apr 23 11:38:20 mx pptpd[26755]: CTRL: Reaping child PPP[26756]
Apr 23 11:38:20 mx pptpd[26755]: CTRL: Client 223.255.253.49 control connection finished
Apr 23 11:38:20 mx pptpd[26755]: CTRL: Exiting now
Apr 23 11:38:20 mx pptpd[26538]: MGR: Reaped child 26755

хотя в chap-secrets есть все:
# Secrets for authentication using CHAP
# client server secret IP addresses

user pptpd 123

клиент (винХР) вываливается с ошибкой 800