Centos 7:
/sbin/iptables -A INPUT -p udp -m policy --dir in --pol ipsec -m udp --dport 1701 -j ACCEPT
/sbin/iptables -A INPUT -p udp -m udp --dport 1701 -j ACCEPT
/sbin/iptables -A INPUT -p udp -m udp --dport 500 -j ACCEPT
/sbin/iptables -A INPUT -p udp -m udp --dport 4500 -j ACCEPT
/sbin/iptables -A INPUT -p esp -j ACCEPT
/sbin/iptables -A INPUT -m policy --dir in --pol ipsec -j ACCEPT
/sbin/iptables -A FORWARD -d 10.0.10.0/24 -j ACCEPT
/sbin/iptables -A FORWARD -s 10.0.10.0/24 -j ACCEPT
/sbin/iptables -A FORWARD -i ppp+ -m state --state NEW,RELATED,ESTABLISHED -j ACCEPT
/sbin/iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
/sbin/iptables -t nat -A POSTROUTING -s 10.0.10.0/24 -o eth0 -j MASQUERADE