一、
当Docker进程启动时，会在主机上创建一个名为docker0的虚拟网桥，此主机上启动的Docker容器会连接到这个虚拟网桥上。虚拟网桥的工作方式和物理交换机类似，这样主机上的所有容器就通过交换机连在了一个二层网络中。
从docker0子网中分配一个IP给容器使用，并设置docker0的IP地址为容器的默认网关。在主机上创建一对虚拟网卡veth pair设备，Docker将veth pair设备的一端放在新创建的容器中，并命名为eth0（容器的网卡），另一端放在主机中，以vethxxx这样类似的名字命名，并将这个网络设备加入到docker0网桥中。可以通过brctl show命令查看。
bridge模式是docker的默认网络模式，不写--net参数，就是bridge模式。使用docker run -p时，docker实际是在iptables做了DNAT规则，实现端口转发功能。可以使用iptables -t nat -vnL查看。
bridge模式如下图所示：
#我本地启动了2个容器
docker pull ubuntu
docker pull nginx
root@arun:~# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
e81696ccf7db ubuntu "bash" 16 minutes ago Up 16 minutes ubuntu-default
64e678f0dc2e nginx "/docker-entrypoint.…" 49 minutes ago Up 49 minutes 80/tcp nginx-default
#(2)从宿主机上看
#其中的docker0为网桥,ens33是vm的网卡,最后的两个veth即为两个容器对应的在docker0上的虚拟网卡,如上图所示;
root@arun:~# ifconfig
docker0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.17.0.1 netmask 255.255.0.0 broadcast 172.17.255.255
inet6 fe80::42:79ff:fe9e:56d1 prefixlen 64 scopeid 0x20<link>
ether 02:42:79:9e:56:d1 txqueuelen 0 (Ethernet)
RX packets 17271 bytes 730406 (730.4 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 17954 bytes 47369915 (47.3 MB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
ens33: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.31.95 netmask 255.255.255.0 broadcast 192.168.31.255
inet6 fe80::20c:29ff:fed0:2fa9 prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:d0:2f:a9 txqueuelen 1000 (Ethernet)
RX packets 113793 bytes 141872357 (141.8 MB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 42423 bytes 3327679 (3.3 MB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1000 (Local Loopback)
RX packets 292 bytes 27086 (27.0 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 292 bytes 27086 (27.0 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
veth9151ca7: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet6 fe80::98f7:91ff:fe22:cf0e prefixlen 64 scopeid 0x20<link>
ether 9a:f7:91:22:cf:0e txqueuelen 0 (Ethernet)
RX packets 12356 bytes 677385 (677.3 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 12517 bytes 36370839 (36.3 MB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
vetha32505c: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet6 fe80::c8c2:b6ff:fee4:38cd prefixlen 64 scopeid 0x20<link>
ether ca:c2:b6:e4:38:cd txqueuelen 0 (Ethernet)
RX packets 4915 bytes 294815 (294.8 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 5468 bytes 11001466 (11.0 MB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
* 可以从docker网络设备管理看出,都哪些容器插到了bridge docker0上:
root@arun:~# docker network ls
NETWORK ID NAME DRIVER SCOPE
405a37e19268 bridge bridge local
3a788fcf07b7 host host local
ab45462b6b41 none null local
#从以下可以看到有哪两个容器连接到了bridage0上:
root@arun:~# docker network inspect 405a37e19268
"Containers": {
"64e678f0dc2e27041c5d0f329a485c4b1d0585e9a9f4db6e6b51de10f08d66d7": {
"Name": "nginx-default",
"EndpointID": "ac7df1259dc70e52f45946d6905510909b27c2681cacb5ea43b7d33194b95dd6",
"MacAddress": "02:42:ac:11:00:02",
"IPv4Address": "172.17.0.2/16",
"IPv6Address": ""
},
"e81696ccf7db9a1fbd3ea199afa7b646fdcd82b1431a387264cdbafd0ad5be7a": {
"Name": "ubuntu-default",
"EndpointID": "a8befcf9167c7433a985dee31eef23cf2024c04de8da100ffefbfb27439ac9ec",
"MacAddress": "02:42:ac:11:00:03",
"IPv4Address": "172.17.0.3/16",
"IPv6Address": ""
}
},
"Options": {
"com.docker.network.bridge.default_bridge": "true",
"com.docker.network.bridge.enable_icc": "true",
"com.docker.network.bridge.enable_ip_masquerade": "true",
"com.docker.network.bridge.host_binding_ipv4": "0.0.0.0",
"com.docker.network.bridge.name": "docker0",
"com.docker.network.driver.mtu": "1500"
},
"Labels": {}
}
]
#Reference: https://segmentfault.com/a/1190000040335988