Ever wonder what TCP/IP.....DNS....DHCP mean?

[Capper]

A Guide By Forum Member Carpenator


Ever wonder what TCP/IP.....DNS....DHCP mean?

In this guide my intention is to give you a basic understanding of TCP/IP. I will talk about where it came from, more important to you where it is now, and what it means to you as a TCP/IP user. So as the saying goes, let’s start at the beginning.

The short story on the beginning of TCP/IP is that the government gave money to educational and research institutions to create a method of communication that would be fault tolerant and far reaching. Now why did they do this? Back then there was this thing called the Cold War in which there were concerns that a foreign threat would blast a few dozen cities resulting in a total loss of data communications. The government wanted a data communications method that could be dynamic enough that if a link went down, the system could reroute traffic through other links so that data would still reach its destination intact.

It took time to get something robust.In fact, it took most of the 1970s, and finally in 1980 most of what we consider TCP/IP was born. Through the eighties you see the further development of local area type networks (using many different protocols) hooking world wide into other servers or networks.

Flash forward to the 1990s, and you see businesses start getting involved in the Internet, not as much for selling and putting information and files up for use believe it or not, it was considered bad etiquette to sell items on the Internet, but to provide connection service.Providers like AOL, Prodigy, and Compuserve were opening Internet gateways so that email could go to people outside of a local network. The ball got rolling, OS/2 included a TCP/IP stack built in, modems started getting faster. Windows 95 came out with its own Internet TCP/IP stack and dialer and whoosh, it was not just a geek thing to be on the Internet. Now you had grandparents and milk truck drivers using TCP/IP to use the Information Superhighway.

So what does this mean to you? It means that, while there are many other protocols out there – some of which I grew up on, you are most likely using TCP/IP on your computer today. TCP/IP made the internet possible and the Internet made it necessary to have TCP/IP loaded on your computer. It became the protocol to use, in most cases, over all others. Where TCP/IP was different than other protocols is that every computer has an IP address, a unique identifier on the network to tell your computer apart from all others.Now when I say network, I am talking about a local set of connected computers, not the Internet. To explain this better, let’s talk about private and public IP addresses.

A public IP address is an address that can be reached by any computer on the Internet. This would be the address that you get from your Internet provider that is used by your firewall/router, or what you receive if have to dial in with a modem (eww).The address takes the form of 4 sets of 3 digits separated by dots (leading zeros are generally dropped). For example, xxx.xxx.xxx.xxx is an IP address. In this case, it’s for Google’s server systems. Each set of three numbers can range from “0” (or “000) to “255”. This means that IP address span from 0.0.0.0 to 255.255.255.255. That’s a great deal of addresses.Of course, many of them are reserved.

Private IP addresses begin with numbers such as 192.168., 10.10, 172.16. These are addresses that were blocked out for private use and can not be routed onto a public network and so can not be reached by other computers on the Internet. Well sorta, what is required is a method to take this private address and allow it to translated into an address that can be used on the Internet. Enter Network Address Translation (NAT), which looks at all the private traffic trying to go out on the internet and then sends it out using a public IP address it has.

As an example of how this works in the real world, you have a computer with the IP of 192.168.1.10. Your computer sends a request to your firewall/router connected to the Internet and has an private (or inside) address of 192.168.1.1, but also has a public or internet) address of 100.202.256.4. What the NAT in your firewall/router does is remember that it received a request from 192.168.1.10 for Internet address 9.8.7.6.Since 9.8.7.6 can not talk to your IP address directly (it is a private address), the firewall/router uses its own public address of 1.2.3.4 to send . Then when the data that it requests comes back it looks up what computer requested it, 192.168.1.10 and sends it there. One way to think about this is your underage child sees a commercial on TV and wants you to order something for them.Since you have to order it for them because the company will not take an order from a child, you make the phone call and give them the credit card number. The order shows up addressed to you and you open it up. You see that it was something that you ordered for your child and you give it to your child without them having any directed interaction with the company that sent it. You can look at the company’s phone number and you street address as a public IP addresses. Your child’s name would be a private IP address and you are the firewall/router.

So we have talked a bit about IP addresses, now let’s talk about how most computers get their IP address and other info. Years back, every computer needed its settings (including IP address) entered into it and then documented so that you didn’t give two computers the same address, a bad thing in the IP world.Then, Dynamic Host Control Protocol, DHCP, came about in 1993 as a method of passing out IP addresses and other information to computers so that they can connect, send, and receive traffic automatically. When your computer is set to automatically obtain its IP information it yells out on the wire to see if there is a computer serving DHCP information. If there is, the DHCP server will send back that it is there and offer your computer IP info and a lease of time it can keep it. Your computer will then request to keep what it was given from the DHCP server. The server will acknowledge the request and let your computer know that it is fine. Now your computer should have everything it needs to connect.

Now where problems start to happen is if you have more than one DCHP server device on the same network. Your computer starts off by saying it is looking for a DHCP server. What it gets back is the equivalent of sellers at a bazaar, “Hey computer, I have a really good IP address, come use mine. “No, I have a really good IP address, request mine.”The more devices you have offering DHCP, the more that speak up.Each DHCP server keeps track of what IP address it gives out, but it does not keep track of what others give out, which can result in all sorts of mess. The moral of this story is that you only want one DHCP server on your network unless you are very knowledgeable and are setting up a DHCP fault tolerance plan, which unless you have 50 computer or more is overkill.

Now about leases, these are in some ways like the lease on an apartment. When you first get the IP address from a DHCP server, a lease for how long you can have it is issued. If you go out to a command prompt and type “ipconfig/all” (without the quotes), you will see the date that your last IP address was given. Now since your computer does not want to get evicted, when the lease is half way up it will ask if it can renew the least for the max time. If it does not hear back, it tries again when half of the remainder of time has gone by. It will keep asking when half has expired until the lease runs out. When the computer boots up it will also do this to make sure it can still use the same IP address. If the DHCP server for some reason does not here the request it will give the IP address to another computer and when your computer regains communication it will get a different IP address instead.

Now that we have beaten IP addresses to a pulp, let’s talk about a part of TCP/IP that mostly gets ignored, but does have a very important part to play, the subnet mask. This is that 255.255.255.0 number that you may have seen, is always used, and just works like that. What this number does is tell your computer which IP addresses are local and which are not. I will not go into much detail about this as I do not want to cause concussions from people head planting into their keyboards. For those of you that still send things through snail mail, you know how inside the post office there is a slot for mail that is local and one for mail that is out of town? For those of you too young, ask your parents or someone else that is really old. What the subnet does is figure out which of IPs are the local IP addresses. What is bad is if the subnet is wrong, it could think that NY is local to Las Vegas and send traffic to the local sorting room which results in data getting thrown on the floor, stepped on, and then thrown in the garbage (not that the USPS people would do that).

Now how does your computer know what to do with the “out of town” traffic? The default gateway comes into play in deciding where to send traffic that the computer does not have a route already designated for (non-local traffic). For the home user, the default gateway will point to your router. The routers default gateway will point to the ISP router and from there it goes into the big Internet cloud until it comes out where you want. Now of course, if your default gateway is wrong, then you are not going to be seeing any of your out of LAN traffic going anywhere.

So hopefully now you have a basic understanding of the IP setup. The thing is, unlike back in the old days when the Internet was called names like ARPANET, we don’t use IP addresses to connect to servers, we use names like HardwareLogic. This is facilitated by a Domain Name System.When you need to call the plumber, most likely you look them up in the phone book or some other reference of phone numbers. DNS does the same type of thing. In your setup you have specified DNS server addresses. When you go to a web site address, if your computer does not remember the site, it will ask the DNS server for the IP address. If the DNS server does not have it, than it will either pass the request on, or it will actively start asking servers above it, just depends on how it was configured.

Where DNS is especially important is response speed. Imagine that you had to go three blocks down to the corner gas station every time that you needed to look up a phone number. On top of this, that phone book is three years old and a third of the pages have been ripped out. Not to mention, if someone is in the phone booth you either have to wait or go another two blocks to a phone book that is in worse shape. If you look at some of the DNS servers provided by the big Internet Service Providers, this is not too much of an exaggeration. This is where you want to research DNS servers on the Internet and look for ones that have a faster response time, better up time, and cache of sites. These things translate to speed on the user end.

Lastly, for completeness I am going to talk about the Windows Internet Naming System, WINS.Back in the day there was Network Neighborhood that eventually became My Network Places. I always thought this was strange since most were not mine and most of them were places I never went. In the beginning this worked by computers just blurting their name out like at a big social. Then it was decided that a master browser would be designate by its OS, a few other variables, and worst case a version of rock, paper, scissors. This made things better in that now one computer was asked where others were, but still not efficient for systems with more than one hub. WINS is a database of computers and their connection info. When a WINS address is entered in the TCP/IP settings it will notify the WINS server when it joins and keep it up to date as it starts the service up each time. This is a system that is going away as what this was used for has been migrated on Microsoft networks into their version of DNS.

Hopefully this has given some understanding of what TCP/IP is and what the settings are used for. I am looking at taking smaller pieces of this and expanding on this in further guides. Your input and feedback is appreciated.

Roger Carpentier has been networking computers for over 11 years starting out with Novell Netware systems. He is currently certified A+, Network+, MCSE in Windows NT and Windows 2000. In the past he was certified by Novell as a CNE, CNE 4, and CNE 5, and Cisco as a CNA. He is currently pursuing his Windows 2003 MCSE.

[wtcnbrwndo4u]

Originally Posted by Capper

Ever wonder what TCP/IP.....DNS....DHCP mean?

No, not really...

Haha, just kidding, informative post! Still to lazy to read though....

[Jokerswild]

My eyes kept glassing over when reading this and I see that I will have to copy it and examine it in depth to understand it fully. That being said I look forward to a more in depth analysis of the pieces. Very nice job of putting it in laymans terms but it is like a dog chasing it's tail from what I can see right now.

[stinger608]

Originally Posted by Jokerswild

My eyes kept glassing over when reading this and I see that I will have to copy it and examine it in depth to understand it fully. That being said I look forward to a more in depth analysis of the pieces. Very nice job of putting it in laymans terms but it is like a dog chasing it's tail from what I can see right now.

Joker you put it so well man!!!!!

[Capper]

Roger is in fact working on a series of articles to explain this better, as well as some other interesting networking stuff.

[Quakindude]

Networking has been a weakness of mine since Windows98 came out. Everything got so easy after that. During Windows 2.x, there was some serious work to be done to get a computer talking to a remote server or when having others connect to yours over the phone lines. I can't recall everything I had to go through for setting up a network cluster in Windows 3.1, but man, that was a full-fledged biotch!

[carpenator]

Hello all,

Consider this an prologue. It was basically intended to be a rough proof of concept article to see if anyone was interested, and if so what about. I also was trying to find out if my writing style was going to work. I was not quite sure about it, but Cap thought it was a good enough start to get feedback, so here it is.

I figure that just out of the content of this article there are enough subjects for at least 10 of the same size or more to explain it out better. I am interested in your constructive feedback for what you would like to see, and what you don't. For instance, is there interest in the history of TCP/IP and/or other networking? It is not really needed, but it can help to put into perspective why things the way they are now.

Thanks,

Roger

[One4yu2c]

Originally Posted by carpenator

It was basically intended to be a rough proof of concept article to see if anyone was interested...

There's always interest in networking, and especially how-to content if you ever feel like tackling it.

[Jokerswild]

I can't even get my 2 home computers to talk to each other and their both running XP pro.

[wtcnbrwndo4u]

Originally Posted by Jokerswild

I can't even get my 2 home computers to talk to each other and their both running XP pro.

Ye olde ****.