Dealing with networks

Goal

This project is about getting to know basic networking concepts of Docker. You will:

create your own network
establish the connection between two containers
create your own IPv6 network with specific subnets

Tools

Try to solve the tasks below independently with the help of the slides and the cheatsheet.
If you have any problems, you will find a fold-out block for each task describing the solution.

Preparation - Setting the VSCode

First make sure that you are back in the workspace folder. In this hands-on we will look at the connection between two containers in different scenarios. This is easiest if the two containers are open side by side in split terminal windows. To do this, open VSCode, open a terminal and click on Split Button . Your VSCode should then look something like this: Split View

Task 1 - Default bridge networks

1.1: Start container

Start a container in the left and right terminal with :

docker run -it --rm corewire/network-playground /bin/bash

For this hands-on, we have created a small Alpine-based container in which network diagnostic tools are pre-installed.

1.2: Find out network information

Find out the IP addresses for both containers with:

ip a

1.3: Test the container connection

Execute the following command in the container in the right terminal:
```
tcpdump icmp
```
The container now monitors all ICMP traffic live, i.e. all PING packets.
Execute a ping in the container in the left terminal to the container in the right terminal:
```
ping <container ip>
```
You can now see in the right-hand terminal how the traffic arrives at the container.

Task 2 - User-defined bridge networks

2.1: Create your own network

Exit the tcpdump in the right terminal with Ctrl+c and leave the container with exit.
Create a new network with the name my-network.

Solution (click on the arrow if you get stuck)

Execute the following command in one of the two terminals:

docker network create my-network

Inspect your network and check which subnet is used in my-network.

Solution (click on the arrow if you get stuck)

Execute the following command in one of the two terminals:

docker network inspect my-network

2.2: Start container with network

Start the container again in the right-hand terminal, but this time with the network you have just created:
```
docker run -it --rm --network=my-network corewire/network-playground /bin/bash
```
Start tcpdump again, query the new IP address with ip a and try, as above, to reach the right container from the left one. This is not successful in this case, as the containers are in different networks.

Solution (click on the arrow if you get stuck)

Execute the following command in the container in the right terminal:

tcpdump icmp

Now find out the new IP with the following command:

ip a

The container now monitors all ICMP traffic live, i.e. all PING packets. Ping the container in the left terminal to the container in the right terminal:

ping <container ip>

You will not see any traffic arriving at the container here, as the containers are in different networks.

Stop the left container with exit.
Start the left container in the new network.

Solution (click on the arrow if you get stuck)

To start the network in the left container, use the following command:

docker run -it --rm --network=my-network corewire/network-playground /bin/bash

Test the connection between the containers again with tcpdump and ping.
The connection is now possible again.

2.3: Using the DNS

Stop both containers again and also start them with a name. This can be set via --name=<container name>.
Test the connection again with tcpdump and ping, using the assigned name as the destination address.

Solution (click on the arrow if you get stuck)

Left terminal:

docker run -it --rm --network=my-network --name=left corewire/network-playground /bin/bash

Right terminal:

docker run -it --rm --network=my-network --name=right corewire/network-playground /bin/bash

tcpdump icmp

Left terminal:

ping right

Task 3: IPv6 networks

Stop both containers again.
Create a new network my-ipv6-network with the specified subnet fd00:0:0:1::/64

Solution (click on the arrow if you get stuck)

To create the network in one of the containers, use the following command:

docker network create --ipv6 --subnet fd00:0:0:1::/64 my-ipv6-network

Now start the two containers in the my-ipv6-network network.

Solution (click on the arrow if you get stuck)

Left terminal:

docker run -it --rm --network=my-ipv6-network --name=left corewire/network-playground /bin/bash

Right terminal:

docker run -it --rm --network=my-ipv6-network --name=right corewire/network-playground /bin/bash

You can now monitor the ipv6 packets with tcpdump icmp6.

Solution (click on the arrow if you get stuck)

Right terminal:

tcpdump icmp6

Left terminal:

ping6 right