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- [Instructor] You can turn any

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ordinary computer into a router.

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Here is what you need.

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Hardware-wise, a second network interface card,

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or NIC, is necessary.

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In terms of software, you could be using

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any Linux distribution.

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Ubuntu is our choice.

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If you're using a physical computer,

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go ahead and plug in your second NIC and set it up.

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A virtual machine, or VM, requires a virtual NIC.

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Here is the big picture view.

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Think of what a home router does.

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It allows you to share a single external IP address

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among multiple hosts in the same local area network, or LAN.

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We call this feature network address translation, or NAT.

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NAT also enables you to forward packets.

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There could be two types of forwarding.

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One is ingress forwarding, meaning forwarding packets

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from outside your network into your network.

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The other is egress, meaning forwarding packets

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from within your network to the outside of your network.

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This diagram shows our overall network architecture

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we're working toward throughout this course.

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In the previous lessons,

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we set up our host firewall on a local host.

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The rest of the architecture

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yet to be completed is grayed out.

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In this chapter, we'll configure

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a second Ubuntu VM host as a router.

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It has two network interface cards,

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network interface card zero, or eth0,

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and network interface card one, or eth1.

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Between these two network interfaces

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is where the forwarding is happening,

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whether it's ingress forwarding or egress forwarding.

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And behind the Ubuntu host as a router,

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you can see an additional host connected

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through a switch the is also connected

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to the Ubuntu host routers NIC1 or eth1.

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What I'm showing you here is precisely

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how your home router works.

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The only difference is that the entire computer,

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namely Ubuntu host, is now dedicated as a router.