1. 环境说明
该环境安装了docker ，并启动了一个容器做了端口映射
iptables 里raw、mangle 表都是空的
// docker 容器
docker ps| grep 43040d1aba46
43040d1aba46 aylei/aliyun-exporter:0.3.1 "python -u /usr/loca…" 2 months ago Up 2 months 9522/tcp, 0.0.0.0:9525->9525/tcp gallant_lumiere
// iptables filter 表 配置
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy DROP)
target prot opt source destination
DOCKER-USER all -- 0.0.0.0/0 0.0.0.0/0
DOCKER-ISOLATION-STAGE-1 all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
DOCKER all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
Chain DOCKER (1 references)
target prot opt source destination
ACCEPT tcp -- 0.0.0.0/0 172.17.0.6 tcp dpt:9525
Chain DOCKER-ISOLATION-STAGE-1 (1 references)
target prot opt source destination
DOCKER-ISOLATION-STAGE-2 all -- 0.0.0.0/0 0.0.0.0/0
RETURN all -- 0.0.0.0/0 0.0.0.0/0
Chain DOCKER-ISOLATION-STAGE-2 (1 references)
target prot opt source destination
DROP all -- 0.0.0.0/0 0.0.0.0/0
RETURN all -- 0.0.0.0/0 0.0.0.0/0
Chain DOCKER-USER (1 references)
target prot opt source destination
RETURN all -- 0.0.0.0/0 0.0.0.0/0
// iptables nat 表配置
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy DROP)
target prot opt source destination
DOCKER-USER all -- 0.0.0.0/0 0.0.0.0/0
DOCKER-ISOLATION-STAGE-1 all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
DOCKER all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
Chain DOCKER (1 references)
target prot opt source destination
ACCEPT tcp -- 0.0.0.0/0 172.17.0.6 tcp dpt:9525
Chain DOCKER-ISOLATION-STAGE-1 (1 references)
target prot opt source destination
DOCKER-ISOLATION-STAGE-2 all -- 0.0.0.0/0 0.0.0.0/0
RETURN all -- 0.0.0.0/0 0.0.0.0/0
Chain DOCKER-ISOLATION-STAGE-2 (1 references)
target prot opt source destination
DROP all -- 0.0.0.0/0 0.0.0.0/0
RETURN all -- 0.0.0.0/0 0.0.0.0/0
Chain DOCKER-USER (1 references)
target prot opt source destination
RETURN all -- 0.0.0.0/0 0.0.0.0/0
[root@yunwei_jenkins-dev_1 ~]# iptables -t nat -nL
Chain PREROUTING (policy ACCEPT)
target prot opt source destination
DOCKER all -- 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type LOCAL
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
DOCKER all -- 0.0.0.0/0 !127.0.0.0/8 ADDRTYPE match dst-type LOCAL
Chain POSTROUTING (policy ACCEPT)
target prot opt source destination
MASQUERADE all -- 172.17.0.0/16 0.0.0.0/0
MASQUERADE tcp -- 172.17.0.6 172.17.0.6 tcp dpt:9525
Chain DOCKER (2 references)
target prot opt source destination
RETURN all -- 0.0.0.0/0 0.0.0.0/0
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:9525 to:172.17.0.6:9525
2. 数据如何经过iptables
接着来梳理，数据经过iptables 是如何处理的。首先需要了解iptables 的组成：
iptables 有4表（raw、mangle、nat、filter）5链（prerouting、input、forward、output、postrouting），数据经过iptables 需要按顺序经过5链进行处理。看下图：
image.png
1、首先数据经过prerouting表，由于 raw、mangle表都为空，所以可以直接看nat表的prerouting 链：
从这里可以看到通过nat表中的prerouting链，将所有访问本地地址的数据都匹配到Docker 链；
而Docker 这里有DNAT 规则，将访问宿主机 9525端口的数据转发到 172.17.0.6:9525
// nat 表
# iptables -t nat -nL
Chain PREROUTING (policy ACCEPT)
target prot opt source destination
DOCKER all -- 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type LOCAL
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
DOCKER all -- 0.0.0.0/0 !127.0.0.0/8 ADDRTYPE match dst-type LOCAL
Chain POSTROUTING (policy ACCEPT)
target prot opt source destination
MASQUERADE all -- 172.17.0.0/16 0.0.0.0/0
MASQUERADE tcp -- 172.17.0.6 172.17.0.6 tcp dpt:9525
Chain DOCKER (2 references)
target prot opt source destination
RETURN all -- 0.0.0.0/0 0.0.0.0/0
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:9525 to:172.17.0.6:9525
2、再到input链，其中mangle表为空，直接看nat、filter表中的input链：
从【1】可以看到nat 中input链以及filter表的input链都没做任何规则
// filter表
# iptables -t filter -nL
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy DROP)
target prot opt source destination
DOCKER-USER all -- 0.0.0.0/0 0.0.0.0/0
DOCKER-ISOLATION-STAGE-1 all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
DOCKER all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
Chain DOCKER (1 references)
target prot opt source destination
ACCEPT tcp -- 0.0.0.0/0 172.17.0.6 tcp dpt:9525
Chain DOCKER-ISOLATION-STAGE-1 (1 references)
target prot opt source destination
DOCKER-ISOLATION-STAGE-2 all -- 0.0.0.0/0 0.0.0.0/0
RETURN all -- 0.0.0.0/0 0.0.0.0/0
Chain DOCKER-ISOLATION-STAGE-2 (1 references)
target prot opt source destination
DROP all -- 0.0.0.0/0 0.0.0.0/0
RETURN all -- 0.0.0.0/0 0.0.0.0/0
Chain DOCKER-USER (1 references)
target prot opt source destination
RETURN all -- 0.0.0.0/0 0.0.0.0/0
3、再接着到output链，raw、mangle为空，直接查看nat、filter表中的output 链
从上可以看到 nat 表中的output链将所有目的地址为非环回地址的本地地址数据匹配到Docker链，然后重复DNAT；
再到filter表中的output链没有做任何规则
4、 最后到postrouting 链，mangle 为空，nat 表将目标地址为0.0.0.0 数据通过SNAT做动态转发出去，而目标地址为172.17.0.6 的则转发到9525 端口
PS：
这是经过朋友的讲解和自己一些理解，如有错误请指正。
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