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An Introduction to IP Addresses

IP addresses are a big factor in firewalls, and also networking in general. As we learned in the previous chapter, every single computer in the world connected to the internet has a unique IP address. This lets someone from Russia send a file to someone in South America without any problems. If you have ever seen an IP address, you might have been confused on how to read it. Don’t worry - we’ll get to the bottom of it!

There’s no place like 127.0.0.1
IP addresses use what is called dotted decimal format. This simply means that an IP address will have four numbers separated by dots - such as 127.0.0.1. We currently use IP version 4, but we eventually all use IP version 6 - which uses six octets separated by dots, instead of just four. (Octet is just a fancy word for each number separated by dots) But why the sudden change? Since all IP addresses must be unique, there are only so many that can come from our current IP version (four octets). Using six octets gives us many more IP addresses to give out, and still have each IP address unique.

Interestingly, you come into direct contact with IP addresses every day and probably aren’t aware of it. When you browse the internet, you can browse the web easily - it’s as easy as typing in www.Google.com! However, not everything is what it seems. What you are actually coming into contact with is the DNS.

A DNS, or domain name system, is a service created to help users such as you to remember how to get to websites. IP addresses aren’t very fun to remember - and guess what? The website you are browsing right now is actually an IP addresses! Which would you rather remember: www.Google.com or http://66.102.9.99?

But not all IP addresses were created equal. We have reserved IP addresses for testing and private networks as well. If you were to go to 127.0.0.1, you would be redirected to your own computer. This is called your loopback domain. The technical department decided to get funny by coining the phrase “There’s no place like 127.0.0.1”. Yes, it’s true we can’t all be comedians.

Lastly, we have private networks. These networks are not able to be accessed from the internet - and thus, they are secure from internet attacks. Any IP address with numbers ranging from the following can be used as private networks:

• 10.0.0.0 to 10.255.255.255
• 172.16.0.0 to 172.31.255.255
• 192.168.0.0 to 192.168.255.255

You’re Bilingual and you don’t even know it!
In understanding IP addresses, we need to understand binary. Binary is a numbering system much like the one you know, which we call the Decimal system. In a sense, you already know two languages - English and Decimal. Don’t worry binary only uses two numbers - 1 and 0!

When you look at the IP address of ”66.102.9.99”, you see that it uses the decimal system - since it uses numbers 0 through 9. Binary only uses 1’s and 0’s. You might ask, then why learn binary if IP addresses use Decimal? The answer is simple: IP addresses are actually composed of binary numbers!

When counting in Binary, you count from right to left. With each position further left, the value of that number is multiplied by two. For instance, the binary number 0001 is equal to 1, while the binary number 0010 is equal to 2. You might ask, then how do we make three? Easy - we place a “1” in the first placeholder too, and get the binary number 0011. Below you can see an example of each power of 2:

Power:
256
128
64
32
Binary: 100000000 010000000 001000000 000100000

Power:
16
8
4
2
1
Binary: 000010000 000001000 000000100 000000010 000000001

And of course we can count to 10 just like in Decimal:

One 0001
Two 0010
Three 0011
Four 0100
Five 0101
Six 0110
Seven 0111
Eight 1000
Nine 1001
Ten 1010

If you’d rather stick to Decimal, don’t worry. Binary will come to you as a second language in due time. You may be confused how we use binary numbers in IP addresses, since IP addresses have numbers 2 through 9. The answer is simple: we use a shorthand notation in IP addresses. The address 255.255.255.0 is actually “11111111.1111111.11111111.00000000” in binary. It’s obviously easier to write in a shorthand notation.

Digging Deeper
We can now say we have learned what exactly an IP address is - a location that is conveyed through binary. Even though we are still in the beginning stages of learning firewalls and security measures, we have learned something vital here: a way to filter content. We can filter out “bad” traffic based on the location of the traffic - or its IP address.

However, this is most commonly used in blocking only specific places - such as a website. Many firewalls setup in schools and workplaces have this type of selective filtering. Oddly enough, we learned our first “black hat” security trick here. When firewalls use this type of filtering, some system administrators forget that you have to block traffic from the IP address and the DNS. If you happen to find that www.Google.com is blocked, try http://66.102.9.99 – it just might work! (Although we don’t condone breaking institutional rules - as you might get in trouble for this if caught.)

While this is banking on the hope that your system administrator is lazy (or doesn’t pay attention to detail), it is still a nice application of what you have now learned.

Closing Comments
We learned an entirely new language in this section - impressive isn’t it? Still, there is a lot to delve into with IP addresses. In the next section, we will take a closer look at IP addresses and how they relate to networks. We will be revisiting binary, so be sure to review this section if you aren’t already familiar with it.

Put up your sails, because we will be learning about ports in the next section! (Ahoy, Mate!)

 
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