Hi. My name is John Cone. Today, in this tutorial, we're going to take a look at layer three addressing. There are six topics that I'd like to discuss with you today. The first one is the difference between Unicast, Multicast, and Broadcast. Then, we'll take a look at IP version four versus IP version six addressing, followed by decimal and binary, and how to convert from one to the other end back. Then, we'll look at the purpose of a Subnet Mask and how Subnet Masks allow us to create subnets, a process called Subnetting. Then, we'll go ahead and take a look at the private address space and network address translation, and how NAT allows us to go from an internal private network out to a public network such as the internet. Lastly, we'll take a look at the Reserved Address Space. The first topic then we'll take a look at again as Unicast, Multicast, and Broadcast. First of all, what is a unicast? Unicast is an IP communication technique that sends packets from one unique source to a unique destination or what we might call a one-to-one communication. Here, the range is going to be any IP address from 1.0.0.0 through 223.255.255.255. As an example of a protocol, we could use TCP. This is used for host-to-host connectivity at the Transport layer, it provides a connection oriented, reliable and ordered, connection as well as air checked delivery of packets making sure that the packets get there. An example of this would be, you send a letter through the post office, and you do like a return receipt, making sure you get some feedback that the letter did arrive as you intended it to be. Another example of this would be just direct communication one-to-one here, such as communication between host 10.5.5.10 and host 192.168.2.200. So, any direct communication between two hosts. The next thing we want to take a look at is a Multicast transmission. This is an IP communication technique that sends packets from one source one multiple destinations or a One-to-Many. Here, our range is going to 224.0.0.0 through 239.255.255.255. Some protocol examples, the first one would be UDP. Now, UDP is right next to TCP, but this is a connectionless transport layer protocol, and this is not reliable. This would be more like sending bulk mail, so you get those flyers, grocery store flyers and coupons in the mail. The people that send those out there, they really don't care if you send back an acknowledgement that you got those. Another example is IGMP, Internet Group Message Protocol. This is a network layer protocol, and it's used by hosts and routers to basically established multicast group memberships. In other words, there's a lot of host out there that use this address range in order to send out a message saying, "hey, is everyone ready to do X, whatever that might be?" Some examples here, sending an email to a mailing list or maybe using streaming media and sending that to a collection of hosts and all school. Example of this was WINS servers on a Windows network would actually use a multicast address in order to find each other and then do WINS replication. The next thing we want to take a look at here, the ideas of a broadcast, what a broadcast is. We have a couple of different kinds of broadcast. First of all, we have a layer 2 broadcast. This is a broadcast over MAC address. This is would be all F's, as you can see here in the slide, and all F's is a way of just broadcasting out to all hosts to the basically the network cards, to the MAC address layer on the network cards. So, here, when a client broadcasts arch for the MAC address of another client, the client can send out all F's, and any NIC card or network card that hears that's going to pull that off the wire, and look at that. The next one is one layer 3 broadcast, an IP address broadcasts, and this is where we're going to send 255.255.255.255 network host. This is an IP communication technique that sends packets from one source one all destinations or what we might call a one-to-all. So, here for example, when the client requires an IP address from a DHCP server, the client broadcast to the range of, again, 255.255.255.255. In effect saying, "hey, is there a DHCP server out there that can give me an IP address?" So, just to give you a quick review again, Unicast, One-to-One, best example like client to a web server, Multicast, One-to-Many, and which case here the destinations have to be able to accept the data from a specific source to receive the traffic stream again like streaming media, and then last of all, we'd have One-to-All, which should be broadcast, and this is really just the easiest way to reach traffic at multiple destinations. Now, where we might run into a problem here would be, if we had some issues with too many broadcast, so we do have another term here that's called a broadcast domain. This is we're all nodes within a network are reachable by broadcast by the same switch, so this would be a layer 2 switch. So, this would be the condition that we find ourselves in when clients are communicating on a VLAN. The problem is where sometimes, you have too much broadcast, and that's what's called a Broadcast storm. This is a loopback condition in which broadcast traffic is constantly repeated throughout the network, this is usually due to a cable being connected into two ports on a same switch, as a friend of mine used to say, "At the place he worked at, they didn't have broadcast storms, they had broadcast hurricanes." So, the next thing here is just a quick simple little illustration between Unicast, Multicast, and Broadcast. Again, you can see here based on the arrows again, One-to-One is unicast, One-to-Many, but not all is multicast, and then finally broadcast goes out to every host that can receive the transmission. Now, let's take a look at IPV4 versus IPV6 Addressing. Here, we have IP version four, this is a logical address represented by 32-bits of 0's and 1's, divided into four octets of 8-bits each, separated by a period. Here's an example. This is the human readable format. That's really converted from binary into decimals, so we can read it. IP version six on the other hand, this is a logical address represented by 128-bits of 0's and 1's divided into eight sections of 16-bits or HEX values each separated by a colon, and that's going to look more like this. So, here, HEX values will be zero through nine and A through F, so zero through nine being 10 digits, A through F being another six for a total 16-bits or 16-bit values. So, when we're looking at communication, we really need to start off with the NIC card, and the NIC card uses what's called a physical MAC address,. Most network technologies, your broadcast based, meaning each network adapter sees every data frame on the wire. The MAC or media access control address or addresses that are hard-coded are burned into the NIC cards. A NIC card will only accept to frame that's addressed to this hard-coded address, it will also accept frames that are broadcast to all NICs on the cable segment. If a computer that I want to communicate with design another cable segment, such as on the other side of a router or switch, those devices will help forward the frame, which brings us up to the next idea which is "ARP"ing, the physical MAC address answers the question really, "Who am I?" based on this burned in hard-coded address. ARPing really says, "Who and where are you?" So, this is a process whereby computers can find each other's Mac address. So, when I want to communicate with your computers, such as computerone.domain.com, my computer will resolve your computer name to an IP address. This is most commonly done through a service such as DNS. Once I have your computer's IP address, I will issue an ARP, an Address Resolution Protocol broadcast to obtain your MAC address. In other words, I will say, "Who out there is 192.168.77.200?" Each computer on the wire will check to see if that is its assigned address, and the computer that has that IP address will in effect respond, "That's me. Here's my MAC address. Please talk directly to this MAC address." This broadcast ethernet frame contains the encapsulated IP address of your computer. This address is then added to an quote ARP cache on the other computer and is used in subsequent communications within the TTL of the cache. If the IP addresses in the other side of a router or switch, there are added steps. If the IP address is on the other side of a router, the computer will have to ARP for the default gateway of the computer and let the router ARP either locally or remotely to forward the frame. If the IP address is on the other side of the switch, the switch will check to see if it knows the MAC address and associated port and forward it accordingly. If it does not know the MAC address, it will forward it out of all ports.
