这台机器上也部署了pptp，pptp已经验证正常。
金山云主机，单网卡
iptables 配置：-A INPUT -p udp -m udp --dport 4500 -j ACCEPT
-A FORWARD -d 172.16.226.0/24 -j ACCEPT
-A FORWARD -s 172.16.226.0/24 -j ACCEPT
-A FORWARD -d 172.16.227.0/24 -j ACCEPT
-A FORWARD -s 172.16.227.0/24 -j ACCEPT
-A FORWARD -m policy --dir in --pol ipsec -j ACCEPT
-A FORWARD -i ppp+ -m state --state NEW,RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
-A OUTPUT -p tcp -m tcp --sport 1723 -j ACCEPT
-A OUTPUT -p gre -j ACCEPT
-A POSTROUTING -s 172.16.226.0/24 -o eth0 -j MASQUERADE
-A POSTROUTING -s 172.16.226.0/24 -o eth0 -j SNAT --to-source 外网IP
-A POSTROUTING -s 172.16.227.0/24 -o eth0 -j MASQUERADE
-A POSTROUTING -s 172.16.227.0/24 -o eth0 -j SNAT --to-source 外网IP