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In this video, you'll learn about network bridges.

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So a bridge is used to introduce a software-defined bridge, and that behaves as a virtualized

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switch.

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Bridges are very common in virtualization and containers.

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They allow you to define an internal network to which your virtual machines or your Docker

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containers can connect.

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And using a bridge allows for creation of an internal network, which is strictly separated

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from the outside using network address translation technology.

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And that means that all the devices that are connected to the bridge are not directly accessible.

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But nodes on the bridge can address external nodes if that is needed.

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But external nodes can only access nodes behind the bridge using port forwarding.

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That's also when why later you are going to learn about Docker containers.

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And when we talk about accessing these containers, you need to configure port forwarding.

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BRCTL command is a common command that can be used to control bridges.

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And bridges can be created through NetPlan or using network manager-related tools.

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But most cases where you will see bridges is in containerized environments.

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Let me show you.

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So here I'm on an Ubuntu virtual machine that I'm using for different purposes.

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And I'm going to show you IP link show.

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And what do we see in IP link show?

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We see Docker 0.

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Now what is this Docker 0?

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Docker 0 is my Docker bridge used by Docker containers.

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And IPA is showing that this Docker bridge has its internal network 172.17.0.1 behind

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all Docker containers are.

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And how about IP route show?

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Well, IP route show defines this internal network.

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And that means that if my host is receiving any incoming requests to 172.17.0.0, it will

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put it on 172.17.0.1.

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And if I would have any Docker containers running, well, this bridge is what is going

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to be used to allow me to access them.

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We'll learn more about that in lesson 21.