借用网上一张图，画的挺好~ 来自http://blog.csdn.net/xinghun_4/article/details/50492041
对应解释如下
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[root@docker3 ~]# iptables -nL -t nat -v
Chain PREROUTING (policy ACCEPT 2 packets, 1152 bytes)
pkts bytes target prot opt in out source destination
10837 3999K KUBE-SERVICES all -- * * 0.0.0.0/0 0.0.0.0/0 /* kubernetes service portals */
====》1. 进入的请求，首先匹配PREROUTING 链里的该规则，并进入KUBE-SERVICES链
238 27286 DOCKER all -- * * 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type LOCAL
Chain INPUT (policy ACCEPT 2 packets, 1152 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 8 packets, 480 bytes)
pkts bytes target prot opt in out source destination
61563 3722K KUBE-SERVICES all -- * * 0.0.0.0/0 0.0.0.0/0 /* kubernetes service portals */
0 0 DOCKER all -- * * 0.0.0.0/0 !127.0.0.0/8 ADDRTYPE match dst-type LOCAL
Chain POSTROUTING (policy ACCEPT 8 packets, 480 bytes)
pkts bytes target prot opt in out source destination
61840 3742K KUBE-POSTROUTING all -- * * 0.0.0.0/0 0.0.0.0/0 /* kubernetes postrouting rules */
====》6. 需要路由到另一个主机的连接经由POSTROUTING该规则，进入KUBE-POSTROUTING 链
62 4323 MASQUERADE all -- * !docker0 10.2.39.0/24 0.0.0.0/0
0 0 MASQUERADE all -- * !docker0 10.1.33.0/24 0.0.0.0/0
Chain DOCKER (2 references)
pkts bytes target prot opt in out source destination
0 0 RETURN all -- docker0 * 0.0.0.0/0 0.0.0.0/0
Chain KUBE-MARK-DROP (0 references)
pkts bytes target prot opt in out source destination
0 0 MARK all -- * * 0.0.0.0/0 0.0.0.0/0 MARK or 0x8000
Chain KUBE-MARK-MASQ (6 references)
pkts bytes target prot opt in out source destination
2 128 MARK all -- * * 0.0.0.0/0 0.0.0.0/0 MARK or 0x4000
Chain KUBE-NODEPORTS (1 references)
pkts bytes target prot opt in out source destination
2 128 KUBE-MARK-MASQ tcp -- * * 0.0.0.0/0 0.0.0.0/0 /* default/k8s-nginx: */ tcp dpt:30780
2 128 KUBE-SVC-2RMP45C4XWDG5BGC tcp -- * * 0.0.0.0/0 0.0.0.0/0 /* default/k8s-nginx: */ tcp dpt:30780
====》3.请求命中上述两个规则，一个进行进入KUBE-MARK-MASQ 链进行标记，一个进入KUBE-SVC-2RMP45C4XWDG5BGC链
Chain KUBE-POSTROUTING (1 references)
pkts bytes target prot opt in out source destination
1 64 MASQUERADE all -- * * 0.0.0.0/0 0.0.0.0/0 /* kubernetes service traffic requiring SNAT */ mark match 0x4000/0x4000
====》7. 执行源地址转换(在flannel网络这里转换的地址是flannel.1即flannel在ifconfig里输出接口的地址），发往另一个node
Chain KUBE-SEP-D5T62RWZFFOCR77Q (1 references)
pkts bytes target prot opt in out source destination
0 0 KUBE-MARK-MASQ all -- * * 10.2.39.3 0.0.0.0/0 /* default/k8s-nginx: */
1 64 DNAT tcp -- * * 0.0.0.0/0 0.0.0.0/0 /* default/k8s-nginx: */ tcp to:10.2.39.3:80
====》5-2. DNAT到本机，交给INPUT
Chain KUBE-SEP-IK3IYR4STYKRJP77 (1 references)
pkts bytes target prot opt in out source destination
0 0 KUBE-MARK-MASQ all -- * * 10.2.39.2 0.0.0.0/0 /* kube-system/kube-dns:dns-tcp */
0 0 DNAT tcp -- * * 0.0.0.0/0 0.0.0.0/0 /* kube-system/kube-dns:dns-tcp */ tcp to:10.2.39.2:53
Chain KUBE-SEP-WV6S37CDULKCYEVE (1 references)
pkts bytes target prot opt in out source destination
0 0 KUBE-MARK-MASQ all -- * * 10.2.39.2 0.0.0.0/0 /* kube-system/kube-dns:dns */
0 0 DNAT udp -- * * 0.0.0.0/0 0.0.0.0/0 /* kube-system/kube-dns:dns */ udp to:10.2.39.2:53
Chain KUBE-SEP-X7YOSBI66WAQ7F6X (2 references)
pkts bytes target prot opt in out source destination
0 0 KUBE-MARK-MASQ all -- * * 172.16.199.17 0.0.0.0/0 /* default/kubernetes:https */
0 0 DNAT tcp -- * * 0.0.0.0/0 0.0.0.0/0 /* default/kubernetes:https */ recent: SET name: KUBE-SEP-X7YOSBI66WAQ7F6X side: source mask: 255.255.255.255 tcp to:172.16.199.17:6443
Chain KUBE-SEP-YXWG4KEJCDIRMCO5 (1 references)
pkts bytes target prot opt in out source destination
0 0 KUBE-MARK-MASQ all -- * * 10.2.4.2 0.0.0.0/0 /* default/k8s-nginx: */
1 64 DNAT tcp -- * * 0.0.0.0/0 0.0.0.0/0 /* default/k8s-nginx: */ tcp to:10.2.4.2:80
====》5-1. DNAT到另一个node，随后执行postrouting
Chain KUBE-SERVICES (2 references)
pkts bytes target prot opt in out source destination
0 0 KUBE-SVC-2RMP45C4XWDG5BGC tcp -- * * 0.0.0.0/0 169.169.148.143 /* default/k8s-nginx: cluster IP */ tcp dpt:80
0 0 KUBE-SVC-NPX46M4PTMTKRN6Y tcp -- * * 0.0.0.0/0 169.169.0.1 /* default/kubernetes:https cluster IP */ tcp dpt:443
0 0 KUBE-SVC-TCOU7JCQXEZGVUNU udp -- * * 0.0.0.0/0 169.169.0.53 /* kube-system/kube-dns:dns cluster IP */ udp dpt:53
0 0 KUBE-SVC-ERIFXISQEP7F7OF4 tcp -- * * 0.0.0.0/0 169.169.0.53 /* kube-system/kube-dns:dns-tcp cluster IP */ tcp dpt:53
2 128 KUBE-NODEPORTS all -- * * 0.0.0.0/0 0.0.0.0/0 /* kubernetes service nodeports; NOTE: this must be the last rule in this chain */ ADDRTYPE match dst-type LOCAL
====》2.连接随后并该规则匹配，进入KUBE-NODEPORTS 链
Chain KUBE-SVC-2RMP45C4XWDG5BGC (2 references)
pkts bytes target prot opt in out source destination
1 64 KUBE-SEP-D5T62RWZFFOCR77Q all -- * * 0.0.0.0/0 0.0.0.0/0 /* default/k8s-nginx: */ statistic mode random probability 0.50000000000
1 64 KUBE-SEP-YXWG4KEJCDIRMCO5 all -- * * 0.0.0.0/0 0.0.0.0/0 /* default/k8s-nginx: */
====》4.请求被该链中两个规则匹配，这里只有两个规则，按照50% RR规则进行负载均衡分发，两个目标链都是进行DNAT，一个转到本node的pod IP上，一个转到另一台宿主机的pod上，因为该service下只有两个pod
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Chain KUBE-SVC-ERIFXISQEP7F7OF4 (1 references)
pkts bytes target prot opt in out source destination
0 0 KUBE-SEP-IK3IYR4STYKRJP77 all -- * * 0.0.0.0/0 0.0.0.0/0 /* kube-system/kube-dns:dns-tcp */
Chain KUBE-SVC-NPX46M4PTMTKRN6Y (1 references)
pkts bytes target prot opt in out source destination
0 0 KUBE-SEP-X7YOSBI66WAQ7F6X all -- * * 0.0.0.0/0 0.0.0.0/0 /* default/kubernetes:https */ recent: CHECK seconds: 10800 reap name: KUBE-SEP-X7YOSBI66WAQ7F6X side: source mask: 255.255.255.255
0 0 KUBE-SEP-X7YOSBI66WAQ7F6X all -- * * 0.0.0.0/0 0.0.0.0/0 /* default/kubernetes:https */
Chain KUBE-SVC-TCOU7JCQXEZGVUNU (1 references)
pkts bytes target prot opt in out source destination
0 0 KUBE-SEP-WV6S37CDULKCYEVE all -- * * 0.0.0.0/0 0.0.0.0/0 /* kube-system/kube-dns:dns */
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本地下载 在被转发目标node的物理网口抓包（需decode as vxlan)
