firewall - выключен
Обнаружил, что когда в интерфейсах появляется ppp0 и тип PPP (PPP Dialup Client) - соединение не происходит.
а когда в интерфейсах появляется ppp0 и тип PPP (PPTP VPN Server) - подключиться получается.
/var/log/messages:
Jan 5 12:40:12 CentOS-55-64-minimal pptpd[6116]: CTRL: Client XXX.XXX.XXX.XXX control connection started
Jan 5 12:40:12 CentOS-55-64-minimal pptpd[6116]: CTRL: Starting call (launching pppd, opening GRE)
Jan 5 12:40:12 CentOS-55-64-minimal pppd[6117]: Plugin /usr/lib64/pptpd/pptpd-logwtmp.so loaded.
Jan 5 12:40:12 CentOS-55-64-minimal pppd[6117]: pptpd-logwtmp: $Version$
Jan 5 12:40:12 CentOS-55-64-minimal pppd[6117]: pppd 2.4.4 started by root, uid 0
Jan 5 12:40:12 CentOS-55-64-minimal pppd[6117]: Using interface ppp1
Jan 5 12:40:12 CentOS-55-64-minimal pppd[6117]: Connect: ppp1 <--> /dev/pts/2
Jan 5 12:40:42 CentOS-55-64-minimal pppd[6117]: LCP: timeout sending Config-Requests
Jan 5 12:40:42 CentOS-55-64-minimal pppd[6117]: Connection terminated.
Jan 5 12:40:42 CentOS-55-64-minimal pppd[6117]: Modem hangup
Jan 5 12:40:42 CentOS-55-64-minimal pppd[6117]: Exit.
Jan 5 12:40:42 CentOS-55-64-minimal pptpd[6116]: 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
Jan 5 12:40:42 CentOS-55-64-minimal pptpd[6116]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7)