Docker Networking

Summary:

1) Bridge Network: Default & Custom

2) Host Network

3) None/Null Network

DOCKER NETWORKING 
In Docker, if 2 containers communicate to each other, it means they are in a network.

Do note that unlike centos, ubuntu does not have ping command in-built. so you need to install it in the containers themselves:

apt-get update

apt-get install iputils-ping  # 333kb 

 

To look at available docker network commands:

Command:-> docker network --help

connect	Connect a container to a network
create	Create a network
disconnect	Disconnect a container from a network
inspect	Display detailed information on one or more networks
ls	List networks
prune	Remove all unused networks
rm	Remove one or more networks

To find all the IP addresses on a system

Command:-> ip a

Find all the networks in docker

Command:-> docker network ls

Types of Networks in Docker

1) Bridge

1a) Default Bridge Network

It is the default network (docker0) in docker, which means if a container is created by default it is created on top of bridge network docker0.

If 2 or more containers get created on the bridge network then they are automatically in the same network, which means they can communicate with each other.

Step 1:- Create container c1 with ubuntu image

docker container run -it --name c1 -d ubuntu

Step 2:- Check c1 container is running on the docker0 network

ip a

you will find one veth.... on docker0

Also, check the CIDR for docker0

Step 3:- Check the IP address of the container, it should be in the CIDR range of the docker0 network. In my case, IP address of c2 is "172.17.0.2"

docker container inspect c1

Step 4:- Create container c2 with centos image

docker container run -it --name c2 -d centos

Step 5:- Check c2 container is running on the docker0 network

ip a

you will find one more veth.... on docker0

Also, check the CIDR for docker0

Step 6:- Check the IP address of the container, it should be in the CIDR range of the docker0 network. In my case IP address of c2 is "172.17.0.3"

docker container inspect c2

Step 7:- Check container c2 ping to c1. It should get a reply from c1 because both are in the same network (default bridge network)

docker exec -it c2 bash

ping 172.17.0.2

 

1b) Custom Bridge Network or User Define Bridge Network

When a network which is created by user or sysadmin so that specified containers can run on it then it is a custom bridge network.

To make your own custom bridge network, follow the steps below:
Step 1: List all the containers

docker network ls

Step 2: Create a new default Bridge network br1 (-d is drive)

docker network create -d bridge br1

Step 3: Verify network is created successfully. It should be listed in docker networks.

docker network ls

Step 4: Inspect br1 network to find more detailed information.

docker network inspect br1

•         "Driver": "bridge",
•         "EnableIPv6": false,
•         "IPAM": {
•             "Driver": "default",
•             "Options": {},
•             "Config": [
•                 {
•                     "Subnet": "172.18.0.0/16",
•                     "Gateway": "172.18.0.1"

Step 4.2: You can create a bridge network with your own subnet

docker network create -d bridge --subnet=192.168.0.0/16 --gateway=192.168.0.1 br2

docker inspect br2

•         "Driver": "bridge",
•         "EnableIPv6": false,
•         "IPAM": {
•             "Driver": "default",
•             "Options": {},
•             "Config": [
•                 {
•                     "Subnet": "192.168.0.0/16",
•                     "Gateway": "192.168.0.1"
•                 }

It means if the containers get created on this network layer then they have IP addresses in 192.168.0.1/16 range.

Step 6:- Create a container on top of br1 network on ubuntu base image.

docker container run -it --name c1 --network br1 -d ubuntu

Step 7: Inspect the container and it should have IP address within the br1 CIDR range.

docker container inspect c1

Step 8: Remove the container and network.

docker rm -f c1

docker network rm br1

docker network ls