In this article we will explore the networking options provided by docker on a single host setup.
Docker provides the basic infrastructure for networking containers in a single host. When
installing docker creates a virtual ethernet bridge called “docker0”. Docker uses the network that
is not in conflict with the host network. When we start the docker service , it will first check
whether we have given a custom bridge option to the docker daemon.if not docker will create its
own bridge called “docker0”
If we run the ifconfig command on host , we can see
docker0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.17.0.1 netmask 255.255.0.0 broadcast 0.0.0.0
inet6 fe80::42:fcff:fed3:c709 prefixlen 64 scopeid 0x20<link>
ether 02:42:fc:d3:c7:09 txqueuelen 0 (Ethernet)
RX packets 50 bytes 3368 (3.2 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 16 bytes 1978 (1.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
While creating this , it will first try to find the network range that is not being used by the host.It
used the ip route command to find the networks that host needs to reach and then finds a range
that does not conflict with any.
As said a virtual ethernet bridge called “docker0” is created.The job of the bridge is to connect 2
different networks and forwards packets from one connected network to the other. The “docker0”
does the same job to all the network interfaces that are connected to this.
Docker provides 3 default networks
[puppet@root$:~]$ docker network ls
NETWORK ID NAME DRIVER SCOPE
064b2749f867 bridge bridge local
2a81b1db3008 host host local
192aee8753a7 none null local
The Bridge,host and None.
Bridge - The bridge network is provided by default and this is the network to which a container
created on this host connects. This maps the “docker0” bridge on the host.
Lets start a Containers and once started check the container ID using
[puppet@root$:~]$ docker ps --format="{{.ID}} {{.Names}}"
2031be9aeaa6 stoic_leavitt
Flat No: 212, 2nd Floor, Annapurna Block, Aditya Enclave, Ameerpet,Hyderabad-16.
E-mail: info@kellytechno.com www.kellytechno.com Ph.No: 040-6462 6789, 998 570 6789.
Now check the bridge network interface using the inspect command as below,
[puppet@root$:~]$ docker network inspect bridge
[
{
"Name": "bridge",
"Id": "064b2749f8678f4429df796d84ae7547a7ccf3e5b9d0b7ea17584195e5628c7f",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "172.17.0.0/16",
"Gateway": "172.17.0.1"
}
]
},
"Internal": false,
"Containers": {
"2031be9aeaa6b47031318ae7c62aaf226d72bd008333e005c7d936fafb85d032": {
"Name": "stoic_leavitt",
"EndpointID":
"a7423df61658290c9e8e9f51fa9f2f357561252b5381616f526e4492b20a2400",
"MacAddress": "02:42:ac:11:00:02",
"IPv4Address": "172.17.0.2/16",
"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": {}
}
]
Flat No: 212, 2nd Floor, Annapurna Block, Aditya Enclave, Ameerpet,Hyderabad-16.
E-mail: info@kellytechno.com www.kellytechno.com Ph.No: 040-6462 6789, 998 570 6789.
In the above output we can see that the container we started uses the bridge network by default.
The entry com.docker.network.bridge.name": "docker0" shows that the bridge is mapped to
docker0. The containers that we create will be added to this network by default and will be
assigned an IP address from the subset of the IPs reserved for bridge. In the above case the
container will be given with IP address from 172.17.0.2/16 range. If we login to the container
and use the ifconfig command like below,
[puppet@root$:~]$ docker exec -it 2031be9aeaa6 ifconfig
eth0 Link encap:Ethernet HWaddr 02:42:ac:11:00:02
inet addr:172.17.0.2 Bcast:0.0.0.0 Mask:255.255.0.0
inet6 addr: fe80::42:acff:fe11:2/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:8 errors:0 dropped:0 overruns:0 frame:0
TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:648 (648.0 B) TX bytes:648 (648.0 B)
We can see that the IP address is assigned based on the Host.
None - This is used to attach a container to a no network.Containers attached to this network will
not have a IP address and will be stand-alone. The none network is useful to create containers
that need to be standalone batch jobs without any dependency on other networks.
Start a Container with the None network as
[puppet@root$:~]$ docker run -dit --net=none ifconfig-ubuntu /bin/bash
ab10aef79d5b3b387ede1197ae7ce63813be7341cf9e1109f57a5813827da76b
Now if we run the ifconfig command inside the container we can see no IP address,
[puppet@root$:~]$ docker exec -it ab10aef79d5b ifconfig
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
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:0
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Host - When a container connects to the Host network , it gets the same configuration of the
host. We can start a container with the host network and then inspect for details.
Flat No: 212, 2nd Floor, Annapurna Block, Aditya Enclave, Ameerpet,Hyderabad-16.
E-mail: info@kellytechno.com www.kellytechno.com Ph.No: 040-6462 6789, 998 570 6789.
Docker Network Commands - Here are the summary of the network commands provided by
docker.
Docker network connect|disconnect <Network Name> <Container> : Connects or disconnects
the containers to the network specified
Docker network inspect <network Name> : inspects the network and provides the details in the
JSON format
Docker network ls : list all the available docker networks
Docker network rm <network Name> : remove the docker network
Docker network create [--driver <driver Name>] <network Name> : creates a network with the
specified driver name taking the driver specified
The driver are generally bridge ,none and host. The driver is a network plugin that adapts the
networking features of docker to the host networking support.
[puppet@root$:~]$ docker network create --driver bridge sample-1
87af01944848c312d4bcf51564bf26a0830b40617074cf3922b9e74673c2cb29
[puppet@root$:~]$ docker network ls
NETWORK ID NAME DRIVER SCOPE
064b2749f867 bridge bridge local
2a81b1db3008 host host local
192aee8753a7 none null local
87af01944848 sample-1 bridge local
[puppet@root$:~]$ docker run -dit ifconfig-ubuntu /bin/bash
b624040483f41c47cb36252dc943953ff461fdfe78790e48760f95158534d637
[puppet@root$:~]$ docker run -dit ifconfig-ubuntu /bin/bash
7f99932627942a352b529e8c98dd8d20a95b8a424298875cb1423e626b32d35e
[puppet@root$:~]$ docker ps --format="{{.ID}} {{.Names}}"
7f9993262794 furious_mccarthy
b624040483f4 gigantic_williams
[puppet@root$:~]$ docker network connect sample-1 furious_mccarthy
[puppet@root$:~]$ docker network connect sample-1 gigantic_williams
[puppet@root$:~]$ docker network inspect sample-1
[
{
"Name": "sample-1",
"Id": "87af01944848c312d4bcf51564bf26a0830b40617074cf3922b9e74673c2cb29",
Flat No: 212, 2nd Floor, Annapurna Block, Aditya Enclave, Ameerpet,Hyderabad-16.
E-mail: info@kellytechno.com www.kellytechno.com Ph.No: 040-6462 6789, 998 570 6789.
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": {},
"Config": [
{
"Subnet": "172.18.0.0/16",
"Gateway": "172.18.0.1/16"
}
]
},
"Internal": false,
"Containers": {
"7f99932627942a352b529e8c98dd8d20a95b8a424298875cb1423e626b32d35e": {
"Name": "furious_mccarthy",
"EndpointID":
"6c5d2810768493e605365bba36633d107a066ea9eba243d0832c92934cec40ea",
"MacAddress": "02:42:ac:12:00:02",
"IPv4Address": "172.18.0.2/16",
"IPv6Address": ""
},
"b624040483f41c47cb36252dc943953ff461fdfe78790e48760f95158534d637": {
"Name": "gigantic_williams",
"EndpointID":
"359b1c392f9345724f44ed07e3067b3f80ee51e269d8f8e172fe72c4c41a3e42",
"MacAddress": "02:42:ac:12:00:03",
"IPv4Address": "172.18.0.3/16",
"IPv6Address": ""
}
},
}
]
[puppet@root$:~]$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS
PORTS NAMES
7f9993262794 ifconfig-ubuntu "/bin/bash" About a minute ago Up About a
minute furious_mccarthy
b624040483f4 ifconfig-ubuntu "/bin/bash" About a minute ago Up About a
minute gigantic_williams
Flat No: 212, 2nd Floor, Annapurna Block, Aditya Enclave, Ameerpet,Hyderabad-16.
E-mail: info@kellytechno.com www.kellytechno.com Ph.No: 040-6462 6789, 998 570 6789.
[puppet@root$:~]$ docker exec -it 7f9993262794 ping -c 4 b624040483f4
PING b624040483f4 (172.18.0.3): 56 data bytes
64 bytes from 172.18.0.3: icmp_seq=0 ttl=64 time=0.047 ms
64 bytes from 172.18.0.3: icmp_seq=1 ttl=64 time=0.056 ms
64 bytes from 172.18.0.3: icmp_seq=2 ttl=64 time=0.052 ms
64 bytes from 172.18.0.3: icmp_seq=3 ttl=64 time=0.049 ms
--- b624040483f4 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.047/0.051/0.056/0.000 ms
In the above example ,we have created a network called “sample-1” . we also created 2
containers and attached them to the sample-1. In order to check whether they are in same
network , we pinged the second container from the first container.
Flat No: 212, 2nd Floor, Annapurna Block, Aditya Enclave, Ameerpet,Hyderabad-16.
E-mail: info@kellytechno.com www.kellytechno.com Ph.No: 040-6462 6789, 998 570 6789.
