CentOS 7.x How to install PPTP VPN

why can't access

Apr  7 18:20:46 conoha pptpd[2985]: CTRL: Starting call (launching pppd, opening GRE)
Apr  7 18:20:46 conoha pppd[2986]: Plugin /usr/lib64/pptpd/pptpd-logwtmp.so loaded.
Apr  7 18:20:46 conoha pppd[2986]: pppd 2.4.5 started by root, uid 0
Apr  7 18:20:46 conoha pppd[2986]: Using interface ppp0
Apr  7 18:20:46 conoha pppd[2986]: Connect: ppp0 <--> /dev/pts/1
Apr  7 18:20:46 conoha NetworkManager[2957]: <info>  (ppp0): new Generic device (carrier: UNKNOWN, driver: 'unknown', ifindex: 13)
Apr  7 18:21:16 conoha pppd[2986]: LCP: timeout sending Config-Requests
Apr  7 18:21:16 conoha pppd[2986]: Connection terminated.
Apr  7 18:21:16 conoha NetworkManager[2957]: <warn>  (ppp0): failed to disable userspace IPv6LL address handling
Apr  7 18:21:16 conoha pppd[2986]: Modem hangup
Apr  7 18:21:16 conoha pppd[2986]: Exit.
Apr  7 18:21:16 conoha pptpd[2985]: GRE: read(fd=6,buffer=611860,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  7 18:21:16 conoha pptpd[2985]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7)

help me~~

solved, firewall problem GRE Protocal 47

reference : http://blog.ivps.kr/61