Misconstrued Thoughts : Yesterday's Misconstrued Thoughts Today

Expert Tuesday (Intro to Networking) by Brent Priddy

Ever wander how the internet works? Hold on for a small technical overview... Don't give up you can understand this!

It is Tuesday again, and the topic de jour is “Networking”… So here it goes. Ity bity history lesson first: the Internet started out as a research project between the US Department of Defense and colleges (where a lot of the initial research and development happened) this was dubbed the dARPAnet. You know how the government loves to play with acronyms, this stands for *inhale* Defense Advanced Research Projects Administration Net. Anyways, the Internet, as you know it today, is just a big mess of computers and routers and switches all connected together, with various networking mediums, to form a big network used for communication.

Here is a picture of what the Internet would look like if it were drawn out like a map, it looks kinda like a snowflake and it actually changes over time or when there is a Denial of Service (DoS) Attack. Think of the Internet like a spider’s web, yes it is a pun since it is called the World Wide Web (WWW), you are not connected to my computer on the internet, but you are connected to your Internet Service Provider (ISP) that is connected to a larger Internet Backbone Service Provider who is connected to blah blah blah … finally to my computer.

How do computers talk to each other? They do by sending and receiving “Packets” of information. Think of packets like little letters mailed from address to address. Your computer, when you are connected to the internet… Let me digress a bit… When you dial into the internet you are THEN connected to the internet, and you lucky cable modem people… you are ALWAYS connected to the internet. When you close your web browser or your email program you are STILL connected to the internet, it is only when you turn your computer off/hang up the connection/turn off the cable modem that you get off of the internet. Sorry, where was I… Oh yes, when you are connected to the Internet you are assigned out an Internet Protocol (IP) address. This is just like your full mailing address, but shorter. It is a four-octet number, like “192.168.0.1”. The numbers are associated to your network you are connected to. Now your ISP, who assigned you the IP address 192.168.0.1 has bunches of IP addresses that they own and these other IP Addresses are kind of like your address, for instance: “192.168.0.2” and “192.168.0.3”. The last number is like the house numbers on your street address, the “192.168.0” part of the address is the SubNetwork Address like your street name.

So do this, on windows ME/XP go to “Start Menu -> Run” and type in “cmd” and hit ok. Enter the command “ipconfig.” For those using windows 98 type in “winipcfg” in the “Start Menu->Run”. From these two places you can figure out your IP address and Subnet Mask (this is what makes the SubNetwork Address).

Ok, you have an address on the internet, how can people talk to you? And Why don’t you just type in the IP address when you want to pull up a web page?!? Well It would be horrible to remember 38.118.142.171 is misconstruedthoughts.com and 216.109.112.135 was yahoo.com oh and brent.isa-geek.org is 12.218.70.172. There is a distributed database of DNS servers (Domain Name System) that translates the name “misconstruedthoughts.com” to 38.118.142.171. By the way misconstruedthoughts.com is the domain and www. misconstruedthoughts.com is the computer in the domain (or network) named www. If jerm had multiple computers within his network misconstruedthoughts.com you would see computername.networkname. misconstruedthoughts.com, it is a hierarchy type of thing.

Ok, so we have that you are on the Internet with your very own IP Address(Which You Can See Where it Is) and you are browsing to Jerm’s web server (which by the way is just a regular computer, nothing special here) to read this page.

What if you wanted to get email from Jerm’s server… how does it know the difference between web pages and email requests? Well again things are numbered. Think of this like your name in your household at your street address. There are multiple people in your house so if someone wants to send a letter to the correct person, you just specify the name. Same for the Internet, when you want to browse to a web server you are going to TCP port 80 and when you want to check email you are connecting to TCP port 25, AOL Instant Messenger connects to TCP port 5190 and the list goes on. Each computer, if there is a network server program running on it, has a list of TCP and UDP ports that they will listen to (names in the household as it were). On XP, do a “netstat” in that command window we opened up earlier. For most people this is unexciting, but for a web server you would see bunches of connections from people all over the world destined to the TCP or UDP ports that you have open on your computer (like TCP port 80 for a web server). From there the conversation would sound like alphabet soup, because communications protocols are all acronyms: PPP, ATM, FR, ISDN, ADSL, HDSL… You could even have conversations where the only nouns that you say were acronyms, sometimes even the acronyms are verbs like “I ARPed for the MAC Address to use to send a BGP Route table change to your IP Address.”
So what is all this hacking stuff I hear about? Well, it is just people finding problems with the communications protocols or with the way that a program was written to cause mischief.

For more information take a look at:

And the networking giant’s what is the internet pags (This is a bit involved though)

Posted by itzjerm at December 7, 2004 01:10 PM