WEBVTT 00:00:00.000 --> 00:00:05.000 align:middle line:84% So an IP Address consists of 2 main portions 00:00:05.000 --> 00:00:10.000 align:middle line:84% we have the Network Address Portion also known as the Network ID 00:00:10.000 --> 00:00:14.000 align:middle line:84% this identifies a specific network, routers maintain routing 00:00:14.000 --> 00:00:19.000 align:middle line:84% tables that contain Network Addresses it's important to realize 00:00:19.000 --> 00:00:22.000 align:middle line:84% that routers build their routing tables based on the Network 00:00:22.000 --> 00:00:27.000 align:middle line:90% Address and not on the host address, so they do not route packets 00:00:27.000 --> 00:00:31.000 align:middle line:84% from 1 interface to another interface based on IP Addresses 00:00:31.000 --> 00:00:35.000 align:middle line:84% they do their routing based on Network Addresses, so they will 00:00:35.000 --> 00:00:39.000 align:middle line:84% look at the destination IP Address in a packet and match that 00:00:39.000 --> 00:00:43.000 align:middle line:84% to a Network Address in their routing table to determine how 00:00:43.000 --> 00:00:47.000 align:middle line:84% traffic is routed. So an IP Address consist of the Network 00:00:47.000 --> 00:00:51.000 align:middle line:84% portion as well as the host portion which is also called 00:00:51.000 --> 00:00:55.000 align:middle line:84% the Host ID, this identifies specific end point on a Network 00:00:55.000 --> 00:01:02.000 align:middle line:84% such as a server, a printer, a PC, an iPhone, an iPad or some 00:01:02.000 --> 00:01:06.000 align:middle line:84% other type of device including IP Phones, these are essentially 00:01:06.000 --> 00:01:09.000 align:middle line:84% devices that need to communicate with each other, so PC may be 00:01:09.000 --> 00:01:14.000 align:middle line:90% communicating with the server, you may be using your iPad to read 00:01:14.000 --> 00:01:20.000 align:middle line:84% the news, so you'll be surfing to cnn.com or usatoday.com 00:01:20.000 --> 00:01:24.000 align:middle line:84% or the BBC, so your iPad is sending traffic to that server and 00:01:24.000 --> 00:01:29.000 align:middle line:84% the server is returning traffic to your iPad, so the iPad and 00:01:29.000 --> 00:01:34.000 align:middle line:90% the server will have a TCP session established at Layer 4 but for 00:01:34.000 --> 00:01:37.000 align:middle line:84% the iPad to communicate with the server, routers need to route 00:01:37.000 --> 00:01:40.000 align:middle line:84% traffic to the server and back again 00:01:40.000 --> 00:01:44.000 align:middle line:84% So here's an analogy to explain Network and host 00:01:44.000 --> 00:01:49.000 align:middle line:84% in cities throughout the world you have streets, so as an 00:01:49.000 --> 00:01:54.000 align:middle line:90% example we have Oxford St., on the street we have multiple houses 00:01:54.000 --> 00:01:59.000 align:middle line:90% or multiple offices but in my example let's assume we have houses 00:01:59.000 --> 00:02:03.000 align:middle line:84% on the street, each house has an individual house number 00:02:03.000 --> 00:02:08.000 align:middle line:84% so we have in this example 1 Oxford St. 2 Oxford St. 00:02:08.000 --> 00:02:14.000 align:middle line:84% 3 Oxford St., 4 Oxford St., 5 Oxford St. and so forth and so on 00:02:14.000 --> 00:02:19.000 align:middle line:84% each house number uniquely identifies that specific house on 00:02:19.000 --> 00:02:24.000 align:middle line:84% this street, now you wouldn't have 2 houses with the same number 00:02:24.000 --> 00:02:28.000 align:middle line:84% on the same street, that would be very confusing because perhaps 00:02:28.000 --> 00:02:32.000 align:middle line:84% you want to meet your friends, the Joneses at #1 Oxford St. 00:02:32.000 --> 00:02:36.000 align:middle line:84% but you may end up spending your day with the totally 00:02:36.000 --> 00:02:39.000 align:middle line:84% different group of people if you have 2 houses with the same 00:02:39.000 --> 00:02:43.000 align:middle line:84% number, in this example we have 2 #1 Oxford St. houses 00:02:43.000 --> 00:02:46.000 align:middle line:84% Which house is the correct house? 00:02:46.000 --> 00:02:51.000 align:middle line:84% Now that's not desirable, when you go to 1 Oxford St. you want 00:02:51.000 --> 00:02:52.000 align:middle line:84% to make sure that you are going to the right house to meet 00:02:52.000 --> 00:02:55.000 align:middle line:84% your friends, rather than going to some other house and hence 00:02:55.000 --> 00:03:00.000 align:middle line:84% house numbers need to be unique on a street 00:03:00.000 --> 00:03:05.000 align:middle line:84% in a City, in the World. Now continuing with our analogy 00:03:05.000 --> 00:03:08.000 align:middle line:84% when working out how to get to remote destination 00:03:08.000 --> 00:03:12.000 align:middle line:84% in the physical world, let's say you want to go to Oxford St. 00:03:12.000 --> 00:03:16.000 align:middle line:84% in London, in the UK and you've never been before 00:03:16.000 --> 00:03:20.000 align:middle line:84% you may use a mapping technologies such as Google Maps to find 00:03:20.000 --> 00:03:24.000 align:middle line:84% out how to get to that specific street, now when you're doing 00:03:24.000 --> 00:03:28.000 align:middle line:84% this you don't look at individual house numbers but rather look 00:03:28.000 --> 00:03:32.000 align:middle line:84% at street names to determine your way to get to that destination 00:03:32.000 --> 00:03:36.000 align:middle line:84% So if you're in different part of London, you may use the street 00:03:36.000 --> 00:03:41.000 align:middle line:90% name to work out how to get from you current street to Oxford St. 00:03:41.000 --> 00:03:46.000 align:middle line:84% and when you get to the destination street then you're able to 00:03:46.000 --> 00:03:50.000 align:middle line:84% look at house numbers to determine which house number to go to 00:03:50.000 --> 00:03:53.000 align:middle line:90% technologies such as Google Maps are obviously really intelligent 00:03:53.000 --> 00:03:57.000 align:middle line:84% and know the house numbers and will guide you to the right 00:03:57.000 --> 00:04:01.000 align:middle line:84% part of the street, but for this analogy thinks of how routers 00:04:01.000 --> 00:04:06.000 align:middle line:84% route, they will route traffic to a destination Network and when 00:04:06.000 --> 00:04:11.000 align:middle line:84% traffic gets to that destination Network then house number are 00:04:11.000 --> 00:04:15.000 align:middle line:84% used or IP Addresses are used to determine which host 00:04:15.000 --> 00:04:16.000 align:middle line:84% to forward the traffic to 00:04:16.000 --> 00:04:22.000 align:middle line:84% Now in a similar way, the Network address in this case 10.1.1.0 00:04:22.000 --> 00:04:26.000 align:middle line:84% identifies a specific network somewhere in the World 00:04:26.000 --> 00:04:31.000 align:middle line:84% Host Addresses such as 1 in this example identify individual 00:04:31.000 --> 00:04:36.000 align:middle line:84% devices on that network, so 1 identifies this PC 00:04:36.000 --> 00:04:41.000 align:middle line:84% on Network 10.1.1.0, each device 00:04:41.000 --> 00:04:45.000 align:middle line:84% on this network has a unique number, so in this example we have 00:04:45.000 --> 00:04:49.000 align:middle line:84% 5 unique devices in the same way that in our previous analogy 00:04:49.000 --> 00:04:53.000 align:middle line:84% we had 5 houses on Oxford St. now in the same way 00:04:53.000 --> 00:04:58.000 align:middle line:84% you wouldn't configure multiple PCs or multiple devices with 00:04:58.000 --> 00:05:02.000 align:middle line:84% the same IP Address as that would cause confusion and conflicts 00:05:02.000 --> 00:05:06.000 align:middle line:84% So as an example, if another device wants to communicate with 00:05:06.000 --> 00:05:10.000 align:middle line:84% 10.1.1.1 which PC would it send the traffic to? 00:05:10.000 --> 00:05:16.000 align:middle line:84% If PC 5 wants to communicate with this host 10.1.1.1 00:05:16.000 --> 00:05:21.000 align:middle line:84% there are 2 hosts with the same IP Address which device should 00:05:21.000 --> 00:05:25.000 align:middle line:84% PC 5 communicates with? So devices on a Network or subnet 00:05:25.000 --> 00:05:29.000 align:middle line:84% which we'll talk more about in a moment have a unique IP Address 00:05:29.000 --> 00:05:33.000 align:middle line:84% in the same way that a house has a unique house number 00:05:33.000 --> 00:05:37.000 align:middle line:84% on a specific street, so in the same way 00:05:37.000 --> 00:05:40.000 align:middle line:84% that we use street names when going from A to B 00:05:40.000 --> 00:05:45.000 align:middle line:84% routers look at Network Addresses to determine how to get 00:05:45.000 --> 00:05:49.000 align:middle line:84% to a remote destination, other protocols such as 00:05:49.000 --> 00:05:53.000 align:middle line:84% Address Resolution Protocol or ARP are used to find 00:05:53.000 --> 00:05:57.000 align:middle line:84% the house number or host number for a host on a specific street 00:05:57.000 --> 00:06:01.000 align:middle line:84% or network, so in this analogy we're going from Queen Anne St. 00:06:01.000 --> 00:06:06.000 align:middle line:84% to Oxford St. and we would use street names for our directions 00:06:06.000 --> 00:06:11.000 align:middle line:84% as per this example, but once we get to this street in this case 00:06:11.000 --> 00:06:14.000 align:middle line:84% Oxford St. we would look for the specific house by looking at 00:06:14.000 --> 00:06:18.000 align:middle line:84% house numbers in the physical world or in the Network world 00:06:18.000 --> 00:06:23.000 align:middle line:84% we would use a protocol such as ARP to find the specific host 00:06:23.000 --> 00:06:27.000 align:middle line:84% on that Network, routers do not make routing decisions 00:06:27.000 --> 00:06:32.000 align:middle line:84% based on IP Addresses and make it based on Network Addresses 00:06:32.000 --> 00:06:36.000 align:middle line:84% A routers routing table is not populated with IP Addresses 00:06:36.000 --> 00:06:40.000 align:middle line:84% it's populated with Network Addresses, the destination 00:06:40.000 --> 00:06:44.000 align:middle line:84% IP Address in a packet is then matched to the routing table 00:06:44.000 --> 00:06:47.000 align:middle line:84% populated with Network Addresses and then a determination 00:06:47.000 --> 00:06:52.000 align:middle line:84% is made to decide out of which port or interface on 00:06:52.000 --> 00:06:57.000 align:middle line:84% the router the packet should be forwarded