In this video, you'll learn about network bridges.
So a bridge is used to introduce a software-defined bridge, and that behaves as a virtualized
switch.
Bridges are very common in virtualization and containers.
They allow you to define an internal network to which your virtual machines or your Docker
containers can connect.
And using a bridge allows for creation of an internal network, which is strictly separated
from the outside using network address translation technology.
And that means that all the devices that are connected to the bridge are not directly accessible.
But nodes on the bridge can address external nodes if that is needed.
But external nodes can only access nodes behind the bridge using port forwarding.
That's also when why later you are going to learn about Docker containers.
And when we talk about accessing these containers, you need to configure port forwarding.
BRCTL command is a common command that can be used to control bridges.
And bridges can be created through NetPlan or using network manager-related tools.
But most cases where you will see bridges is in containerized environments.
Let me show you.
So here I'm on an Ubuntu virtual machine that I'm using for different purposes.
And I'm going to show you IP link show.
And what do we see in IP link show?
We see Docker 0.
Now what is this Docker 0?
Docker 0 is my Docker bridge used by Docker containers.
And IPA is showing that this Docker bridge has its internal network 172.17.0.1 behind
all Docker containers are.
And how about IP route show?
Well, IP route show defines this internal network.
And that means that if my host is receiving any incoming requests to 172.17.0.0, it will
put it on 172.17.0.1.
And if I would have any Docker containers running, well, this bridge is what is going
to be used to allow me to access them.
We'll learn more about that in lesson 21.