VPN за NAT

Имеется сервер CentOS с VPN + AD, перед ним стоит Debian(NAT).

#centos-kvm
$IPT -t nat -A PREROUTING -s xx.xx.33.219 -d xx.xx.1.2 -p tcp -m tcp --dport 1723 -j DNAT --to-destination 192.168.1.5:1723
$IPT -t nat -A PREROUTING -s xx.xx.33.219 -d xx.xx.1.2 -p tcp -m tcp --dport 47 -j DNAT --to-destination 192.168.1.5:47


Mar 30 13:38:02 srv-m pptpd[23379]: CTRL: Client xx.xx.33.219 control connection started
Mar 30 13:38:02 srv-m pptpd[23379]: CTRL: Starting call (launching pppd, opening GRE)
Mar 30 13:38:02 srv-m pppd[23380]: Plugin winbind.so loaded.
Mar 30 13:38:02 srv-m pppd[23380]: WINBIND plugin initialized.
Mar 30 13:38:02 srv-m pppd[23380]: pppd 2.4.5 started by notlive, uid 0
Mar 30 13:38:02 srv-m pppd[23380]: Using interface ppp0
Mar 30 13:38:02 srv-m pppd[23380]: Connect: ppp0 <--> /dev/pts/5
Mar 30 13:38:02 srv-m pptpd[23379]: GRE: read(fd=7,buffer=6097c0,len=8260) from network failed: status = -1 error = Protocol not available
Mar 30 13:38:02 srv-m pptpd[23379]: CTRL: GRE read or PTY write failed (gre,pty)=(7,6)
Mar 30 13:38:02 srv-m pppd[23380]: Modem hangup
Mar 30 13:38:02 srv-m pppd[23380]: Connection terminated.
Mar 30 13:38:02 srv-m kernel: libfcoe_device_notification: NETDEV_UNREGISTER ppp0
Mar 30 13:38:02 srv-m pppd[23380]: Exit.
Mar 30 13:38:02 srv-m pptpd[23379]: CTRL: Client xx.xx.33.219 control connection finished

Дело в том что на сервера Debian(NAT) стоит ВПН сервер.Вот я думаю, может в этом вся проблема?