[转帖]Flannel 环境搭建与分析

flannel,环境,搭建,分析 · 浏览次数 : 0

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**vxlan 模式报文** | 字节 | 值 | |---|---| | 12 | 21:15.194354 | | 21 | 21:15.194372 | | 28 | 2812:21:15.194375 | | 32 | 0x00 | | 40 | 0x00 | | 48 | 172.16.112.133 | | 56 | 172.16.112.130 | | 64 | 0x00 | | 72 | 0x00 | | 80 | 0x00 | | 88 | 0x00 | | 96 | 0x00 | | 104 | 0x00 | | 112 | 0x00 | | 120 | 0x00 | | 128 | 0x00 | | 136 | 0x00 | | 144 | 0x00 | | 152 | 0x00 | | 160 | 0x00 | | 168 | 0x00 | | 176 | 0x00 | | 184 | 0x00 | | 192 | 0x00 | | 196 | 0x00 | | 204 | 0x00 | | 212 | 0x00 | | 220 | 0x00 | | 228 | 0x00 | | 236 | 0x00 | | 244 | 0x00 | | 252 | 0x00 | | 260 | 0x00 | | 268 | 0x00 | | 276 | 0x00 | | 284 | 0x00 | | 292 | 0x00 | | 296 | 0x00 | | 304 | 0x00 | | 312 | 0x00 | | 320 | 0x00 | | 328 | 0x00 | | 336 | 0x00 | | 344 | 0x00 | | 352 | 0x00 | | 360 | 0x00 | | 368 | 0x00 | | 376 | 0x00 | | 384 | 0x00 | | 392 | 0x00 | | 396 | 0x00 | | 404 | 0x00 | | 412 | 0x00 | | 420 | 0x00 | | 428 | 0x00 | | 436 | 0x00 | | 444 | 0x00 | | 452 | 0x00 | | 460 | 0x00 | | 468 | 0x00 | | 476 | 0x00 | | 484 | 0x00 | | 492 | 0x00 | | 496 | 0x00 | | 504 | 0x00 | | 512 | 0x00 | | 520 | 0x00 | | 528 | 0x00 | | 536 | 0x00 | | 544 | 0x00 | | 552 | 0x00 | | 560 | 0x00 | | 568 | 0x00 | | 576 | 0x00 | | 584 | 0x00 | | 592 | 0x00 | | 596 | 0x00 | | 604 | 0x00 | | 612 | 0x00 | | 620 | 0x00 | | 628 | 0x00 | | 636 | 0x00 | | 644 | 0x00 | | 652 | 0x00 | | 660 | 0x00 | | 668 | 0x00 | | 676 | 0x00 | | 684 | 0x00 | | 692 | 0x00 | | 696 | 0x00 |

正文

https://switch-router.gitee.io/blog/flanenl/

介绍

Flannel是CoreOS团队针对Kubernates设计的跨主机容器网络解决方案, 它可以使集群中不同节点上运行的docker容器都具有全集群唯一的虚拟IP地址。

举个例子,在一个由3台主机节点组成系统中,用户希望每个节点上容器的IP地址在各自设定的子网范围内:

Host1: 10.0.1.0/24 Host2: 10.0.2.0/24 Host3: 10.0.3.0/24

但是在 docker 的默认配置中,容器的IP地址是由节点上的 docker 服务自身决定的。以容器默认使用的 bridge 网络为例，其分配到的 IP 地址与 docker0 桥处于同一个网段。而如果没有手动配置，多台主机上的 docker0 的 IP 地址很有可能重复，那么，主机上运行的容器也就有可能被分配到相同的 IP 地址。虽然可以通过手工配置 docker 服务的启动参数(-bip)来使得各个主机的 docker0 桥 IP 地址各异，但这样的手动方式大大增加运维难度。并且除了IP地址，容器间的网络互通还需要配置主机间的 route table，neigh table 等等。而 Flannel 可以使这些工作变得简单。

典型组网

上图为 Flannel 系统运行的典型组网。Flannel 运行在每台需要运行 docker 容器的 host 上，etcd 是一个分布式数据库，它运行在另一台 host 上(实际上，它也可以运行在某台运行 Flannel 的 host 上)，它存储着 Flannel 当前的 IP 资源池以及当前的已分配状况，这是不同 host上的容器 IP 不同的关键。当某台 host 上的 Flannel 启动时，它会访问 etcd 去得到一个空闲的 IP 网段，并将自己已占用该网段的信息写入 etcd ，这样其他 host 就不能分配到同样的网段了。每台运行 Flanne l服务的 host 之间通过 backend 转发跨主机容器之间的网络流量。可选择的 backend 有 host-gw udp vxlan ipip gce alivpc awsvpc等模式，下面将通过实例演示host-gw udp vxlan三种模式。

环境准备

Host1: ubuntu16.04 docker18.06.0ce etcd-3.2.4 对外网卡ens33: 172.16.112.128 Host2: ubuntu16.04 docker18.06.0ce flanneld-0.10 对外网卡ens33: 172.16.112.133 Host3: ubuntu16.04 docker18.06.0ce flanneld-0.10 对外网卡ens33: 172.16.112.130

etcd安装(host1)

1 下载二进制安装包 etcd-v3.2.4-linux-amd64.tar.gz 解压后复制etcd 和 etcdctl到 /usr/local/bin/ 目录 2 创建文件/etc/etcd/etcd.conf

ETCD_DATA_DIR="/var/run/etcd"
ETCD_ADVERTISE_CLIENT_URLS="http://172.16.112.128:2379,http://127.0.0.1:2379"
ETCD_NAME="node-1"
ETCD_LISTEN_CLIENT_URLS="http://172.16.112.128:2379,http://127.0.0.1:2379" 

3 创建 Service 文件/lib/system/system/etcd.service

[Unit]
Description=Etcd Server
Documentation=https://github.com/coreos/etcd
After=network.target
After=network-online.target
Wants=network-online.target
[Service]
User=root
Type=notify
EnvironmentFile=-/etc/etcd/etcd.conf
ExecStart=/usr/local/bin/etcd  
LimitNOFILE=40000
[Install]
WantedBy=multi-user.target 

4 启动Service，可以看到其运行状态正常

root@node-1:~# systemctl start etcd 
systemctl status etcd
● etcd.service - Etcd Server
   Loaded: loaded (/lib/systemd/system/etcd.service; disabled; vendor preset: enabled)
   Active: active (running) since Fri 2018-09-07 03:23:49 PDT; 2 days ago
     Docs: https://github.com/coreos/etcd
 Main PID: 20497 (etcd)
    Tasks: 7
   Memory: 81.9M
      CPU: 8min 46.959s
   CGroup: /system.slice/etcd.service
           └─20497 /usr/local/bin/etcd 

5 创建/etc/flannel-config.json如下（以host-gw为例）

root@node-1:~# cat /etc/flannel-config.json 
{
  "Network":"10.2.0.0/16",
  "SubnetLen":24,
  "Backend":{
      "Type":"host-gw" 
  }
}

6 将之后flannel网络的分配信息存入etcd

root@node-1:~# etcdctl set /docker-subnet/network/config < /etc/flannel-config.json 
{
  "Network":"10.100.0.0/16",
  "SubnetLen":24,
  "Backend":{
      "Type":"host-gw" 
  }
}

flannel 安装(host1)

下载二进制安装包flannel-v0.10.0-linux-amd64.tar.gz 解压后将 flanneld 和mk-docker-opts.sh复制到 /usr/local/bin/ 目录

创建Service文件/lib/system/system/flanneld.service

[Unit]
Description=Flanneld
After=network.target
Before=docker.service
[Service]
User=root
ExecStart=/usr/local/bin/flanneld --etcd-endpoints=http://172.16.112.128:2379 --iface=ens33 -etcd-prefix=/docker-subnet/network
Type=notify
LimitNOFILE=65536 

3 启动flannel服务

root@node-2:~# systemctl start flanneld.service 
root@node-2:~# systemctl status flanneld.service 
● flanneld.service - Flanneld
Loaded: loaded (/lib/systemd/system/flanneld.service; static; vendor preset: enabled)
Active: active (running) since Mon 2018-09-10 01:32:26 PDT; 5s ago
 Main PID: 26076 (flanneld)
 Tasks: 7
Memory: 10.1M
   CPU: 146ms
CGroup: /system.slice/flanneld.service
        └─26076 /usr/local/bin/flanneld --etcd-endpoints=http://172.16.112.128:2379 --iface=ens33 -etcd-prefix=/docker-subnet/network

可以从subnet.env看到从hode-1上获得的子网信息

root@node-2:~# cat /run/flannel/subnet.env 
FLANNEL_NETWORK=10.100.0.0/16
FLANNEL_SUBNET=10.100.50.1/24
FLANNEL_MTU=1500
FLANNEL_IPMASQ=false 

4 执行 mk-docker-opts脚本，得到docker启动参数

root@node-2:~# mk-docker-opts.sh 
root@node-2:~# cat /run/docker_opts.env 
DOCKER_OPT_BIP="--bip=10.100.50.1/24"
DOCKER_OPT_IPMASQ="--ip-masq=true"
DOCKER_OPT_MTU="--mtu=1500"
DOCKER_OPTS=" --bip=10.100.50.1/24 --ip-masq=true --mtu=1500" 

5 修改docker服务参数 /lib/system/system/docker.service

EnvironmentFile=/run/docker_opts.env
ExecStart=/usr/bin/dockerd -H fd:// $DOCKER_OPTS

重新启动docker, 可以看到启动参数中已经有 bip为我们从etcd中获得的网段信息(10.100.50.1/24)了

root@node-2:~# systemctl daemon-reload
root@node-2:~# systemctl restart docker
root@node-2:~# systemctl status docker
● docker.service - Docker Application Container Engine
Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
Active: active (running) since Mon 2018-09-10 01:39:56 PDT; 21s ago
  Docs: https://docs.docker.com
 Main PID: 26664 (dockerd)
 Tasks: 18
Memory: 53.9M
   CPU: 769ms
CGroup: /system.slice/docker.service
        ├─26664 /usr/bin/dockerd -H fd:// --bip=10.100.50.1/24 --ip-masq=true --mtu=1500
        └─26673 docker-containerd --config /var/run/docker/containerd/containerd.toml 

docker0 分配的IP地址也符合预期

root@node-2:~# ifconfig docker0
docker0   Link encap:Ethernet  HWaddr 02:42:d0:bc:0a:1f  
       inet addr:10.100.50.1  Bcast:10.100.50.255  Mask:255.255.255.0
       inet6 addr: fe80::42:d0ff:febc:a1f/64 Scope:Link
       UP BROADCAST MULTICAST  MTU:1500  Metric:1
       RX packets:93 errors:0 dropped:0 overruns:0 frame:0
       TX packets:289 errors:0 dropped:0 overruns:0 carrier:0
       collisions:0 txqueuelen:0 
       RX bytes:5628 (5.6 KB)  TX bytes:27078 (27.0 KB) 

在Host3 上重复此过程，得到的网段地址为10.100.83.0/24

root@node-3:~# ifconfig docker0
docker0   Link encap:Ethernet  HWaddr 02:42:fa:91:74:a1  
       inet addr:10.100.83.1  Bcast:10.100.83.255  Mask:255.255.255.0
       inet6 addr: fe80::42:faff:fe91:74a1/64 Scope:Link
       UP BROADCAST MULTICAST  MTU:1500  Metric:1
       RX packets:114 errors:0 dropped:0 overruns:0 frame:0
       TX packets:275 errors:0 dropped:0 overruns:0 carrier:0
       collisions:0 txqueuelen:0 
       RX bytes:7112 (7.1 KB)  TX bytes:25875 (25.8 KB) 

连通性实验分析

host-gw模式

前面准备环境时，正是按照host-gw方式分配I的

在host2和host3上各运行一个busybox容器来测试其连通性

root@node-2:~# docker run --name bbox2 -tid busybox
759fb9b67f0b21901da1ab6870d3e592bc2923eb0b753d5c009630d5e2c228d5
root@node-2:~# docker exec bbox2 ifconfig
eth0      Link encap:Ethernet  HWaddr 02:42:0A:64:32:02  
          inet addr:10.100.50.2  Bcast:10.100.50.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:18 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:2335 (2.2 KiB)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B) 

root@node-3:~# docker run --name bbox3 -tid busybox
60da1aefb40d9e96984888554cfbc3e927974a6cb1422f679f6a4e2381184385
root@node-3:~# docker exec bbox3 ifconfig
eth0      Link encap:Ethernet  HWaddr 02:42:0A:64:53:02  
          inet addr:10.100.83.2  Bcast:10.100.83.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:18 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:2335 (2.2 KiB)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B) 

此时的组网环境为 host-gw

我们使用ICMP报文来验证其连通性 (同时，使用tcpdump监视host2上的docker0和ens33网卡)

root@node-2:~# docker exec bbox2 ping -c 4 10.100.83.2
PING 10.100.83.2 (10.100.83.2): 56 data bytes
64 bytes from 10.100.83.2: seq=0 ttl=62 time=0.441 ms
64 bytes from 10.100.83.2: seq=1 ttl=62 time=0.384 ms
64 bytes from 10.100.83.2: seq=2 ttl=62 time=0.361 ms
64 bytes from 10.100.83.2: seq=3 ttl=62 time=0.414 ms 

可以看出两个容器之间是可以ping通的。

root@node-2:~# tcpdump -i docker0 -vv
tcpdump: listening on docker0, link-type EN10MB (Ethernet), capture size 262144 bytes
03:50.054787 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 10.100.50.1 tell 10.100.50.2, length 28
03:50.054807 ARP, Ethernet (len 6), IPv4 (len 4), Reply 10.100.50.1 is-at 02:42:d0:bc:0a:1f (oui Unknown), length 28
03:50.054811 IP (tos 0x0, ttl 64, id 52386, offset 0, flags [DF], proto ICMP (1), length 84)
100.50.2 > 10.100.83.2: ICMP echo request, id 3072, seq 0, length 64
03:50.055149 IP (tos 0x0, ttl 62, id 59405, offset 0, flags [none], proto ICMP (1), length 84)
100.83.2 > 10.100.50.2: ICMP echo reply, id 3072, seq 0, length 64
03:51.055498 IP (tos 0x0, ttl 64, id 52420, offset 0, flags [DF], proto ICMP (1), length 84)
100.50.2 > 10.100.83.2: ICMP echo request, id 3072, seq 1, length 64
03:51.055792 IP (tos 0x0, ttl 62, id 59524, offset 0, flags [none], proto ICMP (1), length 84)
100.83.2 > 10.100.50.2: ICMP echo reply, id 3072, seq 1, length 64
03:52.056381 IP (tos 0x0, ttl 64, id 52433, offset 0, flags [DF], proto ICMP (1), length 84) 

root@node-2:~# tcpdump -i ens33 -n icmp -vv
tcpdump: listening on ens33, link-type EN10MB (Ethernet), capture size 262144 bytes
04:57.146397 IP (tos 0x0, ttl 63, id 59135, offset 0, flags [DF], proto ICMP (1), length 84)
16.112.133 > 10.100.83.2: ICMP echo request, id 5888, seq 0, length 64
04:57.146785 IP (tos 0x0, ttl 63, id 8507, offset 0, flags [none], proto ICMP (1), length 84)
100.83.2 > 172.16.112.133: ICMP echo reply, id 5888, seq 0, length 64
04:58.148039 IP (tos 0x0, ttl 63, id 59199, offset 0, flags [DF], proto ICMP (1), length 84)
16.112.133 > 10.100.83.2: ICMP echo request, id 5888, seq 1, length 64
04:58.148295 IP (tos 0x0, ttl 63, id 8744, offset 0, flags [none], proto ICMP (1), length 84)
100.83.2 > 172.16.112.133: ICMP echo reply, id 5888, seq 1, length 64
04:59.148941 IP (tos 0x0, ttl 63, id 59359, offset 0, flags [DF], proto ICMP (1), length 84) 

对比 docker0 和 ens33 上的抓包情况可以看出，原始的 ICMP 报文在从 host2 上，经过了一次SNAT，源IP从容器IP替换成了主机IP

root@node-2:~# iptables -t nat -S
...
-A POSTROUTING -s 10.100.50.0/24 ! -o docker0 -j MASQUERADE
...

分析

在 host-gw 模式中，host3 上 Flannel 启动后，Flannel 会在 host2 上增加一条路由如下，即为 host3 上分配的网段设置下一条网关172.16.112.130.这样，所有在 host2 上，所有目的地址是 host3 上容器IP的报文的下一条都为 host3，且从本地的ens33网卡发出。

root@node-2:~# ip route
...
10.100.83.0/24 via 172.16.112.130 dev ens33 
...

同理，在 host3 上也有相应的路由设置，为目的地址为 host2 所分网段的报文设置下一跳网关

root@node-3:~# ip route
...
10.100.50.0/24 via 172.16.112.133 dev ens33 
...

udp 模式

在 host1 上，编辑 flannel 的网络配置文件，并将配置重新写入 etcd，为了区别，将IP资源池换成 10.101.0.0/16

root@node-1:~# etcdctl set /docker-subnet/network/config < /etc/flannel-config.json 
{
  "Network":"10.101.0.0/16",
  "SubnetLen":24,
  "Backend":{
      "Type":"udp" 
  }
} 

在 host2 和 host3 上重启flannel服务，执行mk-docker-opts.sh脚本，重启 docker 服务

root@node-2:~# systemctl restart flanneld.service 
root@node-2:~# cat /run/flannel/subnet.env 
FLANNEL_NETWORK=10.101.0.0/16
FLANNEL_SUBNET=10.101.83.1/24
FLANNEL_MTU=1472
FLANNEL_IPMASQ=false
root@node-2:~# mk-docker-opts.sh 
root@node-2:~# systemctl restart docker 

host2 分配到 10.101.83.1/24 网段， bbox2 上eth0分配的IP地址为 10.101.83.2/24 host3 分配到 10.101.12.1/24 网段， bbox3 上eth0分配的IP地址为 10.101.12.2/24

查看host2上的路由表

root@node-2:~# ip route
default via 172.16.112.2 dev ens33  proto static  metric 100 
10.101.0.0/16 dev flannel0  proto kernel  scope link  src 10.101.83.0 
10.101.83.0/24 dev docker0  proto kernel  scope link  src 10.101.83.1 
......

注意其中第2条，它表示目的地址是 10.101.0.0/16网段 (排除10.101.83.0/24网段) 的报文都要经过 flannel0 设备转发，那么flannel0 是什么?

root@node-2:~# ip -d link show dev flannel0 
27: flannel0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1472 qdisc pfifo_fast state UNKNOWN mode DEFAULT group default qlen 500
    link/none  promiscuity 0 
    tun 
root@node-2:~# ifconfig flannel0
flannel0  Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:10.101.83.0  P-t-P:10.101.83.0  Mask:255.255.0.0
          inet6 addr: fe80::f837:978c:898b:55ee/64 Scope:Link
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1472  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500 
          RX bytes:0 (0.0 B)  TX bytes:144 (144.0 B) 

可以看出flannel0是一个tun设备，此时的组网环境为 udp

同样使用ICMP报文验证容器之间的连通性 (同时监控docker0 flannel0 ens33上报文)

root@node-2:~# docker exec bbox2 ping -c 4 10.101.12.2
PING 10.101.12.2 (10.101.12.2): 56 data bytes
64 bytes from 10.101.12.2: seq=0 ttl=60 time=3.440 ms
64 bytes from 10.101.12.2: seq=1 ttl=60 time=1.004 ms
64 bytes from 10.101.12.2: seq=2 ttl=60 time=0.898 ms
64 bytes from 10.101.12.2: seq=3 ttl=60 time=0.776 ms 

可以发现，也是可以ping通的。

docker0上的ICMP报文

root@node-2:~# tcpdump -i docker0 -vv
tcpdump: listening on docker0, link-type EN10MB (Ethernet), capture size 262144 bytes
54:12.868669 IP (tos 0x0, ttl 64, id 42742, offset 0, flags [DF], proto ICMP (1), length 84)
101.83.2 > 10.101.12.2: ICMP echo request, id 2816, seq 0, length 64
54:12.870702 IP (tos 0x0, ttl 60, id 21839, offset 0, flags [none], proto ICMP (1), length 84)
101.12.2 > 10.101.83.2: ICMP echo reply, id 2816, seq 0, length 64
54:13.870698 IP (tos 0x0, ttl 64, id 42882, offset 0, flags [DF], proto ICMP (1), length 84)
101.83.2 > 10.101.12.2: ICMP echo request, id 2816, seq 1, length 64
54:13.871515 IP (tos 0x0, ttl 60, id 22088, offset 0, flags [none], proto ICMP (1), length 84)
101.12.2 > 10.101.83.2: ICMP echo reply, id 2816, seq 1, length 64

flannel0上的ICMP报文

root@node-2:~# tcpdump -i flannel0 -vv
tcpdump: listening on flannel0, link-type RAW (Raw IP), capture size 262144 bytes
54:12.868749 IP (tos 0x0, ttl 63, id 42742, offset 0, flags [DF], proto ICMP (1), length 84)
101.83.0 > 10.101.12.2: ICMP echo request, id 2816, seq 0, length 64
54:12.870659 IP (tos 0x0, ttl 61, id 21839, offset 0, flags [none], proto ICMP (1), length 84)
101.12.2 > 10.101.83.0: ICMP echo reply, id 2816, seq 0, length 64
54:13.870725 IP (tos 0x0, ttl 63, id 42882, offset 0, flags [DF], proto ICMP (1), length 84)
101.83.0 > 10.101.12.2: ICMP echo request, id 2816, seq 1, length 64
54:13.871504 IP (tos 0x0, ttl 61, id 22088, offset 0, flags [none], proto ICMP (1), length 84)
101.12.2 > 10.101.83.0: ICMP echo reply, id 2816, seq 1, length 64

ens33 上的UDP报文（ens33上已经抓不到ICMP报文了）

root@node-2:~# tcpdump udp -i ens33 -v 
02:57:09.349575 IP (tos 0x0, ttl 64, id 23956, offset 0, flags [DF], proto UDP (17), length 112)
    172.16.112.133.8285 > node-3.8285: UDP, length 84
02:57:09.349874 IP (tos 0x0, ttl 64, id 31417, offset 0, flags [DF], proto UDP (17), length 112)
    node-3.8285 > 172.16.112.133.8285: UDP, length 84
02:57:10.350543 IP (tos 0x0, ttl 64, id 24046, offset 0, flags [DF], proto UDP (17), length 112)
    172.16.112.133.8285 > node-3.8285: UDP, length 84
02:57:10.350868 IP (tos 0x0, ttl 64, id 31597, offset 0, flags [DF], proto UDP (17), length 112)
    node-3.8285 > 172.16.112.133.8285: UDP, length 84

ICMP报文在传输过程中经过了几次变化：

docker0上 10.101.83.2 > 10.101.12.2
flannel0上 10.101.83.0 > 10.101.12.2
ens33上 172.16.112.133 > 172.16.112.130 内层10.101.83.0 > 10.101.12.2 (内层报文可通过wireshark看出来是一个IP报文)

分析

udp模式中，Flannel会创建 tun 设备 flannel0，所有跨主机流量在内核会通过 flannel0转发，会被 Flannel 用户态读取（第一次报文变化），而在 Flanne l用户态读取后，Flannel会将报文进行隧道封装，将 ICMP 报文外层包裹为 UDP 报文（第二次报文变化） udp2

VxLAN 模式

与之前 udp 模式的修改方式类似，在 host1 上，将backend类型修改为 vxlan，资源池替换为 10.102.0.0/16

root@node-1:~# etcdctl set /docker-subnet/network/config < /etc/flannel-config.json 
{
  "Network":"10.102.0.0/16",
  "SubnetLen":24,
  "Backend":{
      "Type":"vxlan" 
  }
} 

然后重启flannel和docker

host2 分配到 10.102.20.1/24 网段， bbox2 上eth0分配的IP地址为 10.101.20.2/24 host3 分配到 10.102.19.1/24 网段， bbox3 上eth0分配的IP地址为 10.101.19.2/24

查看网卡，可知Flannel为host2创建了一个vxlan设备flannel.1 IP:10.102.20.0/32 MAC: 72:45:d3:56:86:48

root@node-2:~# ip -d link show dev flannel.1 
3: flannel.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UNKNOWN mode DEFAULT group default 
    link/ether 72:45:d3:56:86:48 brd ff:ff:ff:ff:ff:ff promiscuity 0 
    vxlan id 1 local 172.16.112.133 dev ens33 srcport 0 0 dstport 8472 
root@node-2:~# ip addr show dev flannel.1 
3: flannel.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UNKNOWN group default 
    link/ether 72:45:d3:56:86:48 brd ff:ff:ff:ff:ff:ff
    inet 10.102.20.0/32 scope global flannel.1
       valid_lft forever preferred_lft forever 

同理, 在host3上 Flannel.1 IP: 10.102.19.0/32 MAC:d6:1a:65:fc:48:77

root@node-3:~# ip -d link show dev flannel.1 
3: flannel.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UNKNOWN mode DEFAULT group default 
    link/ether d6:1a:65:fc:48:77 brd ff:ff:ff:ff:ff:ff promiscuity 0 
    vxlan id 1 local 172.16.112.130 dev ens33 srcport 0 0 dstport 8472 nolearning ageing 300 udpcsum addrgenmode none 
root@node-3:~# ip addr show dev flannel.1 
3: flannel.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UNKNOWN group default 
    link/ether d6:1a:65:fc:48:77 brd ff:ff:ff:ff:ff:ff
    inet 10.102.19.0/32 scope global flannel.1
       valid_lft forever preferred_lft forever 

在host2上查看其路由表，可以看到Flannel为主机增加了一条跨主机流量的路由

root@node-2:~# ip route
default via 172.16.112.2 dev ens33  proto static  metric 100 
10.102.19.0/24 via 10.102.19.0 dev flannel.1 onlink 
...

再查看其邻居表，可以看到其增加了一条针对 host3 上的 flannel.1 的设置 (d6:1a:65:fc:48:77为 host3 上 flannel.1 的MAC地址,10.102.19.0为IP地址)

root@node-2:~# ip neigh
10.102.19.0 dev flannel.1 lladdr d6:1a:65:fc:48:77 PERMANENT

查看其fdb，可以看到一条设置（其中172.16.112.130为 host3 上的 ens33 的IP地址）

root@node-2:~# bridge fdb
d6:1a:65:fc:48:77 dev flannel.1 dst 172.16.112.130 self permanent 
......

同理 Flannel也为 Host3上进行了相同的配置

此时的组网图为 vxlan

依然使用 busybox 进行 ICMP 通信实验 (同时监控docker0 flanne.1 ens33上的报文情况)

root@node-2:~# docker exec bbox2 ping 10.102.19.2
PING 10.102.19.2 (10.102.19.2): 56 data bytes
64 bytes from 10.102.19.2: seq=0 ttl=62 time=1.287 ms
64 bytes from 10.102.19.2: seq=1 ttl=62 time=1.326 ms
64 bytes from 10.102.19.2: seq=2 ttl=62 time=1.792 ms
64 bytes from 10.102.19.2: seq=3 ttl=62 time=1.653 ms 

依然可以ping通

docker0上的报文如下

root@node-2:~# tcpdump -i docker0 -vv
tcpdump: listening on docker0, link-type EN10MB (Ethernet), capture size 262144 bytes
21:15.194354 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 10.102.20.1 tell 10.102.20.2, length 28
21:15.194372 ARP, Ethernet (len 6), IPv4 (len 4), Reply 10.102.20.1 is-at 02:42:1a:0c:ec:3e (oui Unknown), length 28
21:15.194375 IP (tos 0x0, ttl 64, id 37449, offset 0, flags [DF], proto ICMP (1), length 84)
102.20.2 > 10.102.19.2: ICMP echo request, id 2816, seq 0, length 64
21:15.195431 IP (tos 0x0, ttl 62, id 23004, offset 0, flags [none], proto ICMP (1), length 84)
102.19.2 > 10.102.20.2: ICMP echo reply, id 2816, seq 0, length 64

flanne.1上的报文如下

root@node-2:~# tcpdump -i flannel.1 -vv
tcpdump: listening on flannel.1, link-type EN10MB (Ethernet), capture size 262144 bytes
21:15.194390 IP (tos 0x0, ttl 63, id 37449, offset 0, flags [DF], proto ICMP (1), length 84)
102.20.0 > 10.102.19.2: ICMP echo request, id 2816, seq 0, length 64
21:15.195425 IP (tos 0x0, ttl 63, id 23004, offset 0, flags [none], proto ICMP (1), length 84)
102.19.2 > 10.102.20.0: ICMP echo reply, id 2816, seq 0, length 64
21:16.197793 IP (tos 0x0, ttl 63, id 37695, offset 0, flags [DF], proto ICMP (1), length 84)
102.20.0 > 10.102.19.2: ICMP echo request, id 2816, seq 1, length 64
21:16.198588 IP (tos 0x0, ttl 63, id 23066, offset 0, flags [none], proto ICMP (1), length 84)
102.19.2 > 10.102.20.0: ICMP echo reply, id 2816, seq 1, length 64 

ens33上的udp报文如下:

root@node-2:~# tcpdump udp -i ens33 -vv
tcpdump: listening on ens33, link-type EN10MB (Ethernet), capture size 262144 bytes
12:21:15.194972 IP (tos 0x0, ttl 64, id 28096, offset 0, flags [none], proto UDP (17), length 134)
    172.16.112.133.38092 > node-3.8472: [bad udp cksum 0x39ac -> 0xae89!] OTV, flags [I] (0x08), overlay 0, instance 1
IP (tos 0x0, ttl 63, id 37449, offset 0, flags [DF], proto ICMP (1), length 84)
    10.102.20.0 > 10.102.19.2: ICMP echo request, id 2816, seq 0, length 64
12:21:15.195415 IP (tos 0x0, ttl 64, id 64197, offset 0, flags [none], proto UDP (17), length 134)
    node-3.45840 > 172.16.112.133.8472: [udp sum ok] OTV, flags [I] (0x08), overlay 0, instance 1
IP (tos 0x0, ttl 63, id 23004, offset 0, flags [none], proto ICMP (1), length 84)
    10.102.19.2 > 10.102.20.0: ICMP echo reply, id 2816, seq 0, length 64 

可以看出,与UDP模式相似, vxlan模式也是利用了隧道封装完成跨主机报文的传递

docker0上 10.102.20.2 > 10.102.19.2
flannel0上 10.102.20.0 > 10.102.19.2
ens33上外层 172.16.112.133 > 172.16.112.130 , 内层 10.102.20.0 > 10.102.19.2 (内层报文可通过wireshark看到是一个二层报文)

分析

与UDP模式不同, vxlan模式的报文封装都是在内核完成的, 它是标准的vxlan封装过程,在此过程中,查询了route table, neigh table, fdb table,这也正是 Flannel 为主机内核写入的信息

ICMP request 发送过程:

bbox2 组装ICMP报文但缺少下一跳mac
bbox2 有路由 default via 10.102.20.1 dev eth0, 因此它要首先拿到10.102.20.1 的mac地址,所以它发送ARP报文
docker0 回复 bbox2 其mac地址02:42:1A:0C:EC:3E
bbox2 组装ICMP报文
docker0 收到后, 根据路由 10.102.19.0/24 via 10.102.19.0 dev flannel.1 onlink 将报文转发给 flannel.1, 指定下一跳网关为10.102.19.0 (host3的flannel.1地址), 而由neigh表能查询到其mac为 d6:1a:65:fc:48:77
vxlan 设备 flannel.1 对报文进行处理, 修改除dmac, smac, sip
vxlan 设备flannel.1 对报文进行vxlan封装, 上面的ICMP作为内层报文, 现在组装外层报文由fbd表可查得 dip = 172.16.112.130 sip = IP(host2’s ens33)