添加相应的iptables策略：
添加filter 表的forward链
iptables -I FORWARD -m state -d 192.168.122.0/24 --state NEW,RELATED,ESTABLISHED -j ACCEPT
添加nat 表的prerouting链
iptables -t nat -I PREROUTING -p tcp --dport 1433 -j DNAT --to-destination 192.168.122.242:1433
原文：http://blog.51cto.com/ting2junshui/2045143