Networking 101 – Just the Basics



I have run into so many people who do not understand what an IP address is and the difference between “Public” IP addresses and “Private” IP addresses. So, here is the best way that I know how to describe these terms to someone who is just getting started into understanding these terms and their differences.

First, let’s talk about the mail, not e-mail, that stuff that you have to pick up from your mailbox outside. Each and every letter that you receive has your address on it. Plain and simple, if you live at 100 Smith St, Somewhere, OH 12344, then in order for your mail to be delivered, it must be addressed, right?

Okay, so now that we have that picture in mind, this is basically what an IP address is, it is simply an address that can be found by computers.

Screenshot from Terminal Showing Ping

For instance, in the picture here, we have Google showing as 74.125.227.49. Without that IP address, we would not be able to find Google.com. But, I don’t remember all of these numbers, so how am I supposed to be able to remember the address for Google.com?

This is where DNS (Domain Name System) comes into play. Don’t let these fancy acronyms get you all flustered, this is no more complicated than the Address Book on your phone. When you scroll through your contacts on your phone, you are looking for a name and the phone is going to use a telephone number associated with that name… DNS works the same way.

I type “ping www.google.com” and DNS returns with 74.125.227.49 and then my computer is able to find Google.com. It’s really that simple.

So what is the deal with a Public IP address and Private IP address? If you think of a large office building that has a mailroom, then you already have an idea of how a public IP address works. Let’s say for instance, that a letter gets mailed to the Building address “Attn: John Smith”. The person working in the mailroom is going to take that letter and direct it to John Smith, but the person sending the mail will not exactly know the precise of John Smith’s desk, only the sorter in the mailroom will know. The sorter working in the mailroom is going to assign a box number to each person who receives mail at the building and all mail will be placed into your box. That box is much like a Private IP address.

This is basically what your router does. In order to make sure that packets get to the right place, it takes the packet that is sent to it and routes it to the correct private address without giving any details to anyone outside the building.

So let’s just say that your private mailbox in the mailroom is 192.168.1.34, anytime you receive a letter, the sorter will place your mail into that mailbox; just as a router will forward packets to your private IP address. Again, this happens without you really seeing it and it happens over and over again at a very high rate of speed.

So, let’s trace a packet as it gets delivered by the mailman – it first goes to the mailroom (router) which is located at the public address for the building (IP Address) and then is routed to the private address (Private IP address) by the sorter in the mailroom (Router).

Okay, do you feel like you kind of have a handle on this yet?

Well, let’s look at how some other things fit into this equation. Let’s say for instance that the Sorter knows that John Smith’s private mailbox number is 192.168.1.34, he is going to simply write this on the envelope before putting the mail into that mailbox. This is not different than when a router performs Network Address Translation (NAT) and changes the Public address to a private address.

So to recap, DNS servers can give you the IP address of something out in the public view on the internet. In the example above, I used Google.com, because it is probably a household name at this point. What is important to mention is that DNS Servers cannot see your computer and direct anyone to your computer if you are using a router, they will only be able to see the router (or in the analogy that I used above, the building where you work, but not your office address).

Your router is what helps protect you from an unwanted guest approaching your office and knocking on your door.

So, if you are not using a router between you and the internet, then anyone on the internet has the address directly to your computer and you will have no gatekeeper between you and those unwanted guests.

If you are unsure about whether or not you have a router, it is quite simple, if you have more than one device on your network at home, then you have a router. If you only have one connected device, then you just have to follow a couple quick steps to find out.

On a Windows machine, you would:

  1. click the “Start” Menu
  2. Type “CMD” press Enter (a black box should pop up)
  3. then type “IPCONFIG” press enter
  4. If your IP address starts with 192, 10 or 172; then you are behind a router. If your address is something else, then you are likely public facing to the internet – it is good advice to fix this.

If on a Mac or Linux machine, you would:

  1. Open a Terminal window
  2. Type “IFCONFIG” press Enter
  3. If your IP address starts with 192, 10 or 172; then you are behind a router. If your address is something else, then you are likely public facing to the internet – it is good advice to fix this.

Editorial comment – I have noticed that many Internet Service Providers will readily charge you for Anti-virus protection on a monthly basis, but they overlook the whole part about your computer being public facing to the internet. This is a security concern, no matter what you do on your computer.

So, your computer needs an address so that it can send/receive packets. When connecting to your router, your computer asks for an address and is assigned a private IP address that only can be viewed in your building (on your local area network or LAN).

If your computer is trying to send a packet outside the building (LAN), it will reference an address book (DNS) in order to “dial” the right numbers. Once you get a response from that outside entity, it only sees the address of the building (public IP) not the office number (private IP) of the requester.

So, let’s say that you have a wireless router and anyone can connect to it… Well, this can be an issue in many ways, but the example I prefer to use is very simple to understand. Let’s say that a neighbor connects to your Wifi signal and then they decide to engage in some illegal activity, the only address that is going to be traced is your Public IP that goes to your router. This means that if someone is viewing child pornography or downloading MP3s illegally, this all gets traced back to your house. Is this a good enough reason to secure your Wireless signal? I sure hope so.

I hope that my write up will help someone learn some basics in regards to networking at home. I think it is very important for people to at least have a basic grasp of these concepts. This does not mean that you need to know all of the ports and other designations regarding networking, but I hope this helps bring clarity as to what some of these things mean and why they are important.

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