CHAPTER 6 NETWORK ADDRESSING Networking Basic

CHAPTER 6 NETWORK ADDRESSING Networking Basic



in this lesson we're going to talk about network addressing now it's important that you understand that every host on a particular network has to have an address otherwise we don't know which host information goes to let's take a look down here it's kind of like delivering the mail on the street where you live let's say we've got a street we've got several different cul-de-sacs here and there's a variety of houses all the way along the street if I need to send a letter say from my house here over to my neighbor over here I have to know that neighbor's address in order to be able to send that message to him and if I address my envelope properly I will provide a return address that says this is where the letter came from in case for some reason isn't delivered it can be returned back to me in addition we also specify who the letter is to write their stamp on it and by putting it in the mail the mail person can pick it up and say okay this goes over to here and delivers the mail to that particular person just as the mail needs a dressing so does a computer network each computer that resides on the computer network has to have an address assigned to it so we know where we're sending information in addition just as with the mail we usually assign a return address to things too so we know where the information is coming from and where it's going it's important that you understand that on a computer network you must have unique addresses assigned to computer systems if we look back at the mail example imagine what would happen if three or four different houses on your street all had exactly the same address with that work no because the mail person gets to hold the mails I don't see goes to you know this particular address and there's three different houses that have the same address so you have to kind of guess when well maybe goes to this one the same with computer networks we have to use a unique address for every different host otherwise we have a mess because we don't know who the information is going to or who it's coming from with that in mind you need to understand that there are two different types of addresses used on a computer network there's a physical hardware address and then there's a logical address let's first talk about physical hardware addresses this physical address is also called the MAC address m.a.c which stands for media access control that's the MAC address we have a computer network here and we have several different computers attached to it each computer has a Mac address assigned to it in fact if we were to attach a network printer as well also would have a MAC address the MAC address is a globally unique identifier that's actually burned into the read-only memory of every network interface card so if we have a NIC here network interface card we connect to the network medium with we install this in an expansion slot in the particular computer there's a little ROM chip on here and on that rom chip is the MAC address it comes from the factory each manufacturer of network adapters has a block of addresses assigned to it by the Institute of Electrical and Electronics Engineers called the I Triple E you'll see that a lot the MAC address is a 48 bit value however we usually don't work with it in its binary form what we use is hexadecimal it actually ends up being a 12 character X number for example the MAC address for this network board could be something to the effect of 0 0 0 9 36c too 93 remember that hexadecimal is a base 16 counting system instead of going 0 1 2 3 4 5 6 7 8 9 10 11 12 like we do with decimal with hexadecimal go 0 1 2 3 4 5 6 7 8 9 and then instead of going to 10 we go ABCDE F and in that way we create a hexadecimal MAC address the first six characters 1 2 3 4 5 6 this much of the MAC address is unique to the manufacturer this is a common number that's assigned by the I Triple E to the board manufacturer and all of their network boards MAC addresses start with that particular number the last six characters is a unique hexadecimal number that's assigned to that particular network board it's important to note that hopefully theoretically no two network boards in the world should have the same MAC address they should all be different back in the old days some network boards you could set the MAC address with a couple of dip switches or some jumpers and in you know when you have that kind of situation it is possible to have duplicate MAC addresses today with modern network interface cards you should not ever run into two network boards in the world that have the same MAC address so let's say we have this network right here and we need to send nation from hostei over here to host be well how do we do that addresses we can specify that information go from host a to host B we simply have our piece of information that we're sending and within that information we have what's called a header right up here this is the data this is the data this is the header of a particular piece of information this header will contain the two from for this particular information the two will be the MAC address of the recipient in this case host be the from will be the MAC address of the system that's sending the information in this case host a so that's how the hardware or MAC addresses on a computer network work now when you and I go and set up a computer network we actually don't do a whole lot with MAC addresses because either burned onto the board there's nothing you can chink can change or configure and B we tend to use logical addressing the address host instead of physical addressing understand that every host on the network has a physical hardware address however most of the work we do with these hosts has to do with their logical addresses now a physical address is one that's hardwired into the network interface a logical address is an address that we can assign ourselves and the way we assign it is based on the protocol being used we could assign an IP address if we're using the IP protocol we could assign an IP X address if we're using the IP X protocol and so on we're going to focus here on IP because that is the most widely used protocol today and that's the protocol that you really need to understand we're going back to our Network example that we had before we have our three hosts we have a we have we also have si our network printer now as we said just a minute ago each of these has a physical MAC address but we don't do much with the MAC address instead what I use is its IP address now for instance on this network we could say host a is assigned an address of 192 168 1.1 that is a logical IP address this host could be assigned one ninety two dot one sixty eight dot one dot two this could be one ninety two dot one sixty eight dot one dot three the printer could be one ninety two dot one sixty eight dot one dot four when we send information using logical addresses things work in basically the same way we say okay I have this piece of information that I want to send and in the header instead of specifying a MAC address at this point we specify the IP address we have our to and we have hour from now you're probably saying well what happened to the MAC address don't we do that we do that's actually a process of layering or nesting the information we talked about earlier with the MAC address is still there we just take that information and we encapsulate it inside of an called an IP packet when we say I need to send information from 192 168 1.1 and 192 168 1 2 the network itself doesn't know who these different things are the network deals with the MAC address only so we have to use some type of system that takes and resolves the IP address into a MAC address on an IP network that's done using a protocol called ARP that's address resolution protocol in essence we say hey who is 192 168 1.4 and the ARP protocol is configured to send out a broadcast to all the hosts saying whoever is one ninety two dot one sixty eight dot one dot four will you please send me back your MAC address so this information goes out goes to all the hosts on the network and 192 168 dot one dot one gets it says I'm not four so I don't know who that is same with two two says I'm not four I don't know who that is so it doesn't respond same with three three says I don't know who 192 168 1 dot or is so it ignores it all the host to whom the address doesn't apply they just ignore it however the host that has that address responds back saying hey my MAC address is and then gives it the 12 character hexadecimal number and that way we can resolve these IP addresses into MAC addresses so our network information still has the MAC portion here and we also have our IP portion here this is overly simplified but that's in essence how it works MAC addresses are pretty much straightforward it's a hardware address it's burning the ROM of the chip and that's just the way it is logical addressing is totally different because we can reassign things we can say well you know you used to be one ninety two dot one sixty eight dot one dot for your now one ninety two dot one sixty eight dot one dot five it works the reason we can get away with that is because of ARP even though we changed the logical address art will go out again and check and say hey who is 192 168 1.4 and the host that now has that address will respond with its new MAC address and that way we can get away with

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