Frequently (Un)Asked Questions – Pt. 2

Frequently (Un)Asked Questions – Pt. 2

Recently, I was teaching a class, and a student asked what meant in a firewall policy. I then spent time explaining the tenets of subnets and IP addressing. This wasn’t the first time I have had a student look confused or ask a question on the subject. Therefore, today’s blog will discuss the ideas of IP addresses and MAC addresses.

Scenario: You want to send a letter to your friend in your town. What information do you need? Their street address? Their city? Their state? Their zip code? For something local, you could probably put the street address of your friend, and the post office will get it there.

Comparing this to scenario to networking: when you want to send information to someone on your Local Area Network (LAN), all you need is their local address, or MAC address. This address is a unique unchangeable* address that is used for local communication. MAC addresses usually take the form FF:FF:FF:FF:FF:FF and can be found on many computers rather simply.

Note: the first six digits of a MAC address denote the company that produced the electronic device. For example, F4:5C:89 belongs to Apple. So you know that the screenshot above was taken on an Apple computer.

Now let’s go back to our scenario and introduce IP addresses.

Scenario: You want to send a letter to your parents in a different town from your own. What information do you need? Definitely their street address. We need to tell the post office which city they live in, what state that city is in, and what their zip code is. This helps the post office avoid sending things destined for Springfield, Illinois to Springfield, Ohio instead.

Again, comparing this to the world of networking: is not hosted in your house. How does your computer send data to Google? And how does Google send data back? IP addresses. These addresses are what computers use to send non-local information (read: data that goes past the boundaries of your local router).

Let’s look at the example again, but put it in computer terms.

Example: My computer ( wants to send something to ( My computer will make a letter to and send it to the post office (router). To send something to the router, my computer (F4:5C:89:XX:XX:XX) will use the local address of the router (08:EA:44:XX:XX:XX). So my computer puts the letter to google in an envelope, writes google’s address on it. Then puts that envelope in a box and addresses the box to my router.

So that is a basic run down of how MAC addresses work versus IP addresses. Next time, I will discuss Network Address Translation (NAT) and subnetting.

See you next time!

Further down: Classful NetworkingClassless Inter-Domain RoutingWhy do we need IPv6?




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