One More Reason to Love Your Router: It Can Assign IP Addresses

Recently, I tackled a question about the firewall in your router and how it works to keep your data safe from harm — an excellent reason to use a router, even if you’re running a single PC on your network. But the firewall isn’t the only security trick up your router’s sleeve. In fact, when you connect to the Internet through a router, to the outside world, your system doesn’t even exist.

Huh?

Think about the definition of the word router. At its core, the device you plug in between your desktop and your DSL or cable modem has but one purpose: to route. Technically, your router is a gateway — it takes on the IP address that your modem would otherwise assign to your computer and, in return, assigns a different set of IP addresses to connected systems (wirelessly or otherwise).

These internal IP addresses typically come with a prefix of 192.XXX — the X's standing in for the rest of the 32-bit string — although you can usually specify addresses on your router’s configuration screen. (Don’t get me started on the differences between static and dynamic IP addresses — we’ll be here all night.)

When your system queries another networked server somewhere on the Internet — to download a file, for example — the packets of data don’t go straight to your computer. They’re processed by your router, a kind of digital mail carrier that forwards the information onto the system that requested it. Of course, the mail has to go through inspection, and this is basically what a firewall does, but it also handles the task I’m talking about here: network address translation.

If you employ a router on your network, try this trick: Hit up the website, WhatismyIP.com on two devices within your network. These can be a mobile phone in Wi-Fi mode, a connected desktop PC, a laptop — anything. When I do this, what do I see? The same IP address: my D-Link router’s.

Because of your router’s ability to assign IP addresses, the router’s own address effectively shields any number of local systems. This maintains the confidentiality of your connected devices while your router takes all the heat from external, unknown sources looking to infiltrate your system. To them, your entire network looks like a standard desktop device. How little they know!

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