Now try pinging a host that is not within your subnet, such as 192.168.50.17. Type

Understanding Internet Protocol | 83 Table 4-6 Class A subnetting matrix N ET ID S UBNET ID H OST ID M ASK OF U SABLE S UBNETS OF H OSTS PER 8 0 24 255.0.0.0 8 NA 16,777,14 8 1 23 255.128.0.0 9 NA NA 8 2 22 255.192.0.0 10 2 4,194,302 8 3 21 255.224.0.0 11 6 2,097,150 8 4 20 255.240.0.0 12 14 1,048,574 8 5 19 255.248.0.0 13 30 524,286 8 6 18 255.252.0.0 14 62 262,142 8 7 17 255.254.0.0 15 126 131,070 8 8 16 255.255.0.0 16 254 65,534 8 9 15 255.255.128.0 17 510 32,766 8 10 14 255.255.192.0 18 1,022 16,382 8 11 13 255.255.224.0 19 2,046 8,190 8 12 12 255.255.240.0 20 4,094 4,094 8 13 11 255.255.248.0 21 8,190 2,046 8 14 10 255.255.252.0 22 16,382 1,022 8 15 9 255.255.254.0 23 32,766 510 8 16 8 255.255.255.0 24 65,534 254 8 17 7 255.255.255.128 25 131,070 126 8 18 6 255.255.255.192 26 262,142 62 8 19 5 255.255.255.224 27 524,286 30 8 20 4 255.255.255.240 28 1,048,574 14 8 21 3 255.255.255.248 29 2,097,150 6 8 22 2 255.255.255.252 30 4,194,302 2 8 23 1 255.255.255.254 31 NA NA 8 24 0 255.255.255.255 32 NA NA 84 | Lesson 4 Table 4-7 Class B subnetting matrix N ET ID S UBNET ID H OST ID M ASK OF U SABLE S UBNETS OF H OSTS PER 16 0 16 255.255.0.0 16 NA 65,534 16 1 15 255.255.128.0 17 NA NA 16 2 14 255.255.192.0 18 2 16,382 16 3 13 255.255.224.0 19 6 8,190 16 4 12 255.255.240.0 20 14 4,094 16 5 11 255.255.248.0 21 30 2,046 16 6 10 255.255.252.0 22 62 1,022 16 7 9 255.255.254.0 23 126 510 16 8 8 255.255.255.0 24 254 254 16 9 7 255.255.255.128 25 510 126 16 10 6 255.255.255.192 26 1,022 62 16 11 5 255.255.255.224 27 2,046 30 16 12 4 255.255.255.240 28 4,094 14 16 13 3 255.255.255.248 29 8,190 6 16 14 2 255.255.255.252 30 16,382 2 16 15 1 255.255.255.254 31 NA NA 16 16 0 255.255.255.255 32 NA NA Table 4-8 Class C subnetting matrix N ET ID S UBNET ID H OST ID M ASK OF U SABLE S UBNETS OF H OSTS PER 24 0 8 255.255.255.0 24 NA 254 24 1 7 255.255.255.128 25 NA NA 24 2 6 255.255.255.192 26 2 62 24 3 5 255.255.255.224 27 6 30 24 4 4 255.255.255.240 28 14 14 24 5 3 255.255.255.248 29 30 6 24 6 2 255.255.255.252 30 62 2 24 7 1 255.255.255.254 31 NA NA 24 8 0 255.255.255.255 32 NA NA Understanding Internet Protocol | 85 Defining Classless Inter-Domain Routing CIDR Classless inter-domain routing CIDR is a way of allocating IP addresses and routing Internet Protocol packets. It was intended to replace the prior classful IP addressing architec- ture in an attempt to slow the exhaustion of IPv4 addresses. Classless inter-domain routing is based on variable-length subnet masking VLSM, which allows a network to be divided into different-sized subnets to make one IP network that would have previously been consid- ered a class such as Class A look like Class B or Class C. This can help network administra- tors efficiently use subnets without wasting IP addresses. One example of CIDR would be the IP network number 192.168.0.016. The 16 means that the subnet mask has 16 masked bits or 1s making 255.255.0.0. Usually, that would be a default Class B subnet mask, but because we are using it in conjunction with what used to be a Class C network number, the whole kit and caboodle becomes classless. CONFIGURE A CIDR-BASED IP NETWORK GET READY. In this exercise, you will configure two computers with classless private IP addresses, then verify the configuration through the use of ipconfig and ping. In this particular exercise, the IP network 10.254.254.0, which would have previously appeared to be a Class A network, will use a Class C subnet mask. This effectively makes it classless:

1. Access the Local Area Connection Properties dialog box.

2. Click Internet Protocol Version 4, then click the Properties button. This displays the

Internet Protocol Version 4 Properties dialog box. Write down the current settings so that you can return the computer to these settings at the end of the exercise.

3. Click the Use the following IP address radio button. This enables the other fields so

you can type in the IP information. Enter the following: • For the IP address of the fi rst computer, enter 10.254.254.115. • For the IP address of the second computer, enter 10.254.254.116. • For the Subnet mask of both computers, enter 255.255.255.0. This would be written out as 10.254.254.024, signifying that we are creating a classless 10.254.254.0 network with a subnet mask that has 24 masked bits. • Leave the Default gateway and the Preferred DNS server fi elds blank. • When you are fi nished, the fi rst computer’s confi guration should look like Figure 4-10. Figure 4-10 IPv4 Properties dialog box configured with a classless IP address 86 | Lesson 4 4. Click OK. Then, in the Local Area Connection Properties dialog box, click OK. This will complete and bind the configuration to the network adapter.

5. Now test your configuration. We will do this in two ways, first with the ipconfig com-

mand, and second with the ping command. a. Type ipconfi g. Verify that the IP confi guration is accurate and corresponds to what you typed in the IP Properties window. If not, go back and check your Internet Protocol Properties dialog box.

b. Ping the other computer. Also try to ping any other computers that were con-

fi gured as part of this classless network for example, ping 10.254.254.116. Make sure you get replies. If you do not, check the IP confi gurations of both computers, watch for IP confl icts, and make sure the computers are physically connected to the same network. ■ Working with IPv6 IPv6 is the new generation of IP addressing for the Internet, but it can also be used in small office networks and home networks. It was designed to overcome the limitations of IPv4, including address space and security. THE BOTTOM LINE CERTIFICATION READY How do you define IPv6? 3.3 Understanding IPv6 Before you can configure IPv6, you first need to understand a few concepts, some of which are similar to IPv4, but others of which are quite different. In this section, we will categorize the types of IPv6 addresses and specifically explain why IPv6 is to be the suc- cessor to IPv4. Remember, IPv4 is still the dominant IP protocol in today’s world. IPv6 has been defined for over a decade, and it has slowly been gaining acceptance in the networking world, although it is still considered in its infancy. The number-one reason to use IPv6 is address space. IPv6 is a 128-bit system, whereas its still-dominant predecessor IPv4 is only a 32-bit system. What does this mean? Well, whereas IPv4 can have approximately 4 billion IP addresses in the whole system, IPv6 can have 340 undecillion addresses. That’s 340 with 36 zeroes after it Of course, various limitations in the system will reduce that number, but the final result is still far greater than with the IPv4 system. Yet another reason to use IPv6 is advanced integrated security; for example, IPSec is a fundamental component of IPv6 we will discuss IPSec in more depth in Lesson 6. IPv6 also has many advancements and simplifications when it comes to address assignment. Table 4-9 summarizes some of the differences between IPv4 and IPv6. Table 4-9 IPv4 versus IPv6 IP V 4 IP V 6 32-bit 4 billion addresses 128-bit 340 undecillion addresses Less security in general More security, IPsec is mandatory na Simplification of address assignment