安装软件：
yum install epel-release
yum install openswan xl2tpd ppp lsof
1./etc/ipsec.conf
config setup protostack=netkey dumpdir=/var/run/pluto/ nat_traversal=yes virtual_private=%v4:10.0.0.0/8,%v4:192.168.0.0/16,%v4:172.16.0.0/12,%v4:25.0.0.0/8,%v4:100.64.0.0/10,%v6:fd00::/8,%v6:fe80::/10 conn L2TP-PSK-NAT rightsubnet=vhost:%priv also=L2TP-PSK-noNAT conn L2TP-PSK-noNAT authby=secret pfs=no auto=add keyingtries=3 dpddelay=30 dpdtimeout=120 dpdaction=clear rekey=no ikelifetime=8h keylife=1h type=transport left=xxx.xxx.xxx.xxx leftprotoport=17/1701 right=%any rightprotoport=17/%any