Полдключаюсь к pptpd из Windows XP.
Раз, два - подключение проходит нормально.
Jan 18 14:34:10 pmbc pptpd[19472]: CTRL: Client 193.110.17.24 control connection started
Jan 18 14:34:10 pmbc pptpd[19472]: CTRL: Starting call (launching pppd, opening GRE)
Jan 18 14:34:10 pmbc pppd[19473]: Plugin /usr/lib/pptpd/pptpd-logwtmp.so loaded.
Jan 18 14:34:10 pmbc pppd[19473]: pptpd-logwtmp: $Version$
Jan 18 14:34:10 pmbc pppd[19473]: pppd 2.4.3 started by root, uid 0
Jan 18 14:34:10 pmbc pppd[19473]: Using interface ppp0
Jan 18 14:34:10 pmbc pppd[19473]: Connect: ppp0 <--> /dev/pts/2
Jan 18 14:34:10 pmbc pptpd[19472]: GRE: Bad checksum from pppd.
Jan 18 14:34:10 pmbc pptpd[19472]: CTRL: Ignored a SET LINK INFO packet with real ACCMs!
Jan 18 14:34:10 pmbc ppp(pam_unix)[19473]: session opened for user fes by (uid=0)
Jan 18 14:34:10 pmbc pppd[19473]: user fes logged in
Jan 18 14:34:10 pmbc pppd[19473]: PAP peer authentication succeeded for fes
Jan 18 14:34:10 pmbc pppd[19473]: found interface eth1 for proxy arp
Jan 18 14:34:10 pmbc pppd[19473]: local  IP address <my_inet_ip>
Jan 18 14:34:10 pmbc pppd[19473]: remote IP address <my_local_ip>
Jan 18 14:34:10 pmbc pppd[19473]: pptpd-logwtmp.so ip-up ppp0 fes <client_ip>

Отключаюсь.

Пытаюсь подключиться снова:

Jan 18 15:28:32 pmbc pptpd[20429]: CTRL: Client <client_ip> control connection started
Jan 18 15:28:32 pmbc pptpd[20429]: CTRL: Starting call (launching pppd, opening GRE)
Jan 18 15:28:32 pmbc pppd[20430]: Plugin /usr/lib/pptpd/pptpd-logwtmp.so loaded.
Jan 18 15:28:32 pmbc pppd[20430]: pptpd-logwtmp: $Version$
Jan 18 15:28:32 pmbc pppd[20430]: pppd 2.4.3 started by root, uid 0
Jan 18 15:28:32 pmbc pppd[20430]: Using interface ppp0
Jan 18 15:28:32 pmbc pppd[20430]: Connect: ppp0 <--> /dev/pts/1
Jan 18 15:28:32 pmbc pptpd[20429]: GRE: Bad checksum from pppd.
Jan 18 15:29:02 pmbc pppd[20430]: LCP: timeout sending Config-Requests
Jan 18 15:29:02 pmbc pppd[20430]: Connection terminated.
Jan 18 15:29:02 pmbc pppd[20430]: Using interface ppp0
Jan 18 15:29:02 pmbc pppd[20430]: Connect: ppp0 <--> /dev/pts/1
Jan 18 15:29:02 pmbc pppd[20430]: tcflush failed: Bad file descriptor
Jan 18 15:29:02 pmbc pppd[20430]: tcsetattr: Invalid argument (line 1016)
Jan 18 15:29:02 pmbc pppd[20430]: Exit.
Jan 18 15:29:02 pmbc pptpd[20429]: GRE: read(fd=6,buffer=804e5a0,len=8196) from PTY failed: status = -1 error = Input/output error, usually caused by unexpected termination of pppd, check option syntax and pppd logs
Jan 18 15:29:02 pmbc pptpd[20429]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7)
Jan 18 15:29:02 pmbc pptpd[20429]: CTRL: Client <client_IP> control connection finished
Jan 18 15:29:13 pmbc hal.hotplug[20460]: timout(10000 ms) waiting for /class/net/ppp0

Что за лажа? У кого-то есть идеи?
p.s. За это время я не менял ни конфиги сервера, ни настройки параметров VPN подключения на винде клиента.
F1!