0 背景

目的需求：
SNAT：实现没有公网IP的ECS实例借助有公网的ECS访问外网
环境需求：
首先有公网的主机与没有公网的主机必须同一个VPC安全组（确保两个主机内网互通才可以）

1 详细步骤

1、开启端口转发。
vim /etc/sysctl.conf
2、增加：
net.ipv4.ip_forward = 1
3、持久化：
sysctl -p
4、iptables -t nat -I POSTROUTING -s 192.168.20.52/32 -j SNAT --to-source 192.168.20.50
5、查看规则
#iptables -t nat -L
6、在控制台配置路由表
7、配置 FORWARD 链规则
#允许来自内网服务器的转发流量
sudo iptables -I FORWARD 1 -s 172.22.31.77 -j ACCEPT

#允许返回流量（状态跟踪）
sudo iptables -I FORWARD 2 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
8、参考链接：
https://developer.aliyun.com/article/607330?spm=5176.smartservice_service_robot_chat_new.0.0.1d7643ecxgFIta
https://blog.csdn.net/qq_39626154/article/details/114691370
https://blog.csdn.net/weixin_51369125/article/details/134334942?utm_medium=distribute.pc_relevant.none-task-blog-2_defaultbaidujs_baidulandingword~default-5-134334942-blog-114691370.235^v43pc_blog_bottom_relevance_base5&spm=1001.2101.3001.4242.4&utm_relevant_index=8
https://blog.csdn.net/xglinux/article/details/126536553?spm=1001.2101.3001.6650.3&utm_medium=distribute.pc_relevant.none-task-blog-2%7Edefault%7EBlogCommendFromBaidu%7ERate-3-126536553-blog-114691370.235%5Ev43%5Epc_blog_bottom_relevance_base5&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2%7Edefault%7EBlogCommendFromBaidu%7ERate-3-126536553-blog-114691370.235%5Ev43%5Epc_blog_bottom_relevance_base5&utm_relevant_index=6
https://blog.csdn.net/ck784101777/article/details/139347915
https://blog.csdn.net/xiaoxinla/article/details/118159253?spm=1001.2101.3001.6650.6&utm_medium=distribute.pc_relevant.none-task-blog-2%7Edefault%7EBlogCommendFromBaidu%7ERate-6-118159253-blog-139347915.235%5Ev43%5Epc_blog_bottom_relevance_base5&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2%7Edefault%7EBlogCommendFromBaidu%7ERate-6-118159253-blog-139347915.235%5Ev43%5Epc_blog_bottom_relevance_base5&utm_relevant_index=13
https://blog.csdn.net/weixin_46389364/article/details/109393899?spm=1001.2101.3001.6650.5&utm_medium=distribute.pc_relevant.none-task-blog-2%7Edefault%7EBlogCommendFromBaidu%7ERate-5-109393899-blog-139347915.235%5Ev43%5Epc_blog_bottom_relevance_base5&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2%7Edefault%7EBlogCommendFromBaidu%7ERate-5-109393899-blog-139347915.235%5Ev43%5Epc_blog_bottom_relevance_base5&utm_relevant_index=10