1 00:00:00,300 --> 00:00:07,140 In the section, we're going to discuss network address translation or NAT and Port Address translation 2 00:00:07,140 --> 00:00:10,750 or PAT, we'll discuss why next is required. 3 00:00:11,070 --> 00:00:14,100 Why do we use Nat in networks today? 4 00:00:14,760 --> 00:00:21,390 We'll also discuss the difference between NAT and PAT and we'll discuss the Cisco term overloading, 5 00:00:21,660 --> 00:00:29,260 which implies NAT, a lot of network engineers talk about NAT even though they actually mean PAT. 6 00:00:29,790 --> 00:00:32,670 So we need to understand the differences between those two terms. 7 00:00:33,010 --> 00:00:38,030 And as always, I'd like to demonstrate how to set up NAT using the command line interface. 8 00:00:38,520 --> 00:00:46,890 We'll look at different types of NAT, including static NAT, dynamic NAT and PAT, or overloading, as Cisco 9 00:00:46,890 --> 00:00:47,340 call it. 10 00:00:48,850 --> 00:00:50,170 Before going any further. 11 00:00:51,490 --> 00:00:56,470 Here's s a demonstration, I've disabled all network interface cards on my PC. 12 00:00:57,860 --> 00:01:04,170 Except for the wireless interface card, when I look at the details of that card, I can see that my 13 00:01:04,190 --> 00:01:08,270 IP address is 192.168.189 14 00:01:08,660 --> 00:01:12,500 and I'll have a default gateway of 192.168.254. 15 00:01:13,960 --> 00:01:18,670 I can view that in a CMD prompt as an example, so on my PC 16 00:01:19,540 --> 00:01:24,040 type IP config, see the IP address, see the default gateway. 17 00:01:25,320 --> 00:01:28,560 I can ping Google.com. 18 00:01:32,830 --> 00:01:36,130 So notice I'm getting replies from Google.com. 19 00:01:37,270 --> 00:01:47,290 I can access Google.com, so here's the Google website, but when I type what is my IP address into 20 00:01:47,290 --> 00:01:47,860 Google. 21 00:01:48,710 --> 00:01:52,430 I'm told by Google that this is my public IP address. 22 00:01:53,410 --> 00:01:54,070 So 23 00:01:56,520 --> 00:02:03,390 IP config again shows me that my internal IP address or private IP address is 192.1 24 00:02:03,390 --> 00:02:05,250 68.189 25 00:02:05,580 --> 00:02:08,070 but my public IP address is this. 26 00:02:11,910 --> 00:02:19,380 So in this example, my Internet router at home is connected to the Internet and this router is configured 27 00:02:19,380 --> 00:02:25,520 with DHCP, it's allocating IP addresses to devices internally using DHCP 28 00:02:26,370 --> 00:02:30,420 and one of those IP addresses was allocated to my local PC 29 00:02:30,990 --> 00:02:35,760 but when I go onto the Internet, my address used is a public IP address. 30 00:02:36,360 --> 00:02:38,100 So network address translation. 31 00:02:39,040 --> 00:02:45,310 essentially translates a private IP address, which is non-routable on the Internet to a publicly 32 00:02:45,310 --> 00:02:52,180 routable IP address, your public IP address is typically allocated to you by your service provider, 33 00:02:52,480 --> 00:03:00,370 which in my case is British Telecom or BT here in the U.K. In larger networks, companies may register 34 00:03:00,370 --> 00:03:02,260 their own public IP addresses. 35 00:03:03,400 --> 00:03:05,560 Here are some well-known examples. 36 00:03:06,780 --> 00:03:18,120 Hewlett Packard owned 15.0.0.0/8 and 16, Apple own 17, MIT 18, Ford 19 37 00:03:18,630 --> 00:03:20,190 AT&T 32. 38 00:03:21,150 --> 00:03:26,790 and so on, and IBM, as an example, 9.0.0.0. 39 00:03:27,730 --> 00:03:37,030 So as an example, if you're working within HP or within Apple, you may not be using a private IP address 40 00:03:37,030 --> 00:03:42,610 such as this, you may actually have a public IP address allocated to your PC. 41 00:03:43,120 --> 00:03:49,030 These are globally routable public IP addresses that were registered by some of the largest companies 42 00:03:49,030 --> 00:03:49,660 in the world. 43 00:03:50,440 --> 00:03:52,550 But IP addresses are running out. 44 00:03:53,020 --> 00:03:58,630 So in most small medium businesses today, you'll be using a private IP address internally.