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If you already have such a device on your network providing these services, then 
there's nothing for you to do. You can skip this section. But if you'd like to set up 
your own router, then feel free to proceed.
If you'd like to proceed and set up a router, then the first order of business is to 
decide which device on your network will serve that purpose. Often, administrators 
will build DNS, DHCP, and routing services all into the same server, so you can 
even use the same device you've used earlier to work through the DNS and DHCP 
examples for our purposes in this section. In order for a device to function as a 
gateway, it should have at least two network interfaces, one to your ISP device (such 
as a cable modem) and another interface connected to a network switch that your 
other servers will connect to. The interface connected to your ISP device should use 
DHCP, so it will obtain an IP address directly from your ISP. This interface may 
need a static IP with details provided from the ISP, if relevant.
Depending on what kind of internet connection you have, Linux itself can likely 
replace whatever device your internet modem connects to. A good example of this is 
a cable modem that your office or home router may utilize. In this case, the modem 
provides your internet connection, and then your router allows other devices on 
your network to access it. In some cases, your modem and router may even be the 
same device. Therefore, depending on the hardware you have, this method of setting 
up your networking may or may not be efficient. But if you do have the hardware 
available, you'll be able to manage the entire networking stack with Ubuntu Server 
quite easily.
Why might you want to create 
your own internet gateway? One potential reason is 
that it's often the case that security patches aren't provided for commercial routers 
and firewall devices. New vulnerabilities are discovered all the time, and if your 
router or firewall is no longer supported by the manufacturer, it may allow outside 
threats into your network. By setting up an internet gateway with Ubuntu, you'll 
benefit from the regular updates that Canonical provides. As long as you're using a 
version of Ubuntu that's still supported (such as an LTS release, as is the case with 
Ubuntu 20.04), you'll benefit from a more secure platform. If nothing else, a physical 
server that we can install Ubuntu on will usually have a more powerful CPU than a 
commercial device would have, which would mean that CPU bottlenecks slowing 
down network performance would be less likely to happen.
Thankfully, setting up an internet gateway is easy. In fact, we'll only need to execute 
a single command to set up routing between interfaces, which is technically all that's 
required in order to set up an internet gateway. But before we get into that, it's also 
important to keep in mind that if you do set up an internet gateway, you'll need to 
pay special attention to security. The device that sits between your network and your 
modem will be a constant attack target, just like any other gateway device would be. 
When it comes to commercial routers, they're also attacked constantly. 

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Setting Up Network Services