Traditional Options for Subnetting a /24 Address Block in C#.NET

Encoder QR in C#.NET Traditional Options for Subnetting a /24 Address Block

Network Address Internal subnet mask: 255.255.255.0 Internal subnet mask: 255.255.255.128 Internal subnet mask: 255.255.255.192 Internal subnet mask: 255.255.255.224

In situations such as these, you can assign different subnet masks to different subnets. This option will allow you to accommodate your specific network needs without having to acquire new address space from your provider. Figure 1-38 illustrates how you can use subnet masks of various lengths to accommodate three subnets of 100, 50, and 20 hosts, respectively. This particular network configuration will allow for up to four more subnets to be added later.

Subnet B: 50 computers Subnet ID: 10

Subnet A: 100 computers Subnet ID: 0

208.147.66.128/26

Subnet C: 20 computers Subnet ID: 110

208.147.66.192/27

When you use VLSMs to divide your network into subnets of varying sizes, the address block is divided up a specific way. If you have a /22 network, for example, you can use VLSMs to divide the network into one /23 network, one /24 network, one /25 network, and so on. If, on the other hand, you have a /24 network as in the example presented in Table 1-7, you can use VLSMs to divide it up into one /25 network, one /26 network, one /27 network, and so on. Also, note that whenever you use VLSMs, a specific pattern of subnet IDs composed of 1s and a single trailing 0 must be used. The trailing 0 in each subnet ID prevents the address space in each subnet from overlapping with the address space in other subnets. When the subnet IDs with VLSMs are fixed in the specific pattern shown in Table 1-7, subnets do not overlap, and the addresses can be interpreted unambiguously.

208.147.66.0/24

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Table 1-7

Subnet ID (Binary) 0 10 110 1110 11110 111110 111111 Subnet Mask 255.255.255.128 255.255.255.192 255.255.255.224 255.255.255.240 255.255.255.248 255.255.255.252 255.255.255.252 Hosts per Subnet 126 62 30 14 6 2 2 Example Subnet Address 208.147.66.0/25 208.147.66.128/26 208.147.66.192/27 208.147.66.224/28 208.147.66.240/29 208.147.66.248/30 208.147.66.252/30

In Table 1-7, notice that the seventh and final subnet listed is the same size as the sixth and is distinguished by an all-1s subnet ID instead of by the trailing 0 used with the other subnet IDs. As an alternative to using the maximum seven subnets presented, you could define the all-1s subnet ID at any level in the table to replace all the subnets listed below that subnet. For example, you could define a subnet ID of 11 to replace subnets 3 through 7 listed in the table. Exam Tip Just about everyone considers VLSMs confusing. If you see a question on VLSMs on the 70-642 exam, and you very well might, it will probably be the toughest question you will face on the whole test. To handle such questions, first try to eliminate incorrect answer choices whose subnet masks do not match the appropriate incremental pattern. Then, try to eliminate answer choices whose address ranges do not properly correspond to the pattern of 1s with a single trailing 0. You might need to perform decimal-to-binary conversions to get the answer correct. Most of all, though, make sure you don t spend too much time on a VLSM question. Eliminate what you can, and if you don t have an answer within 3 minutes or so, take your best guess and move on.

In this practice, you perform exercises that help solidify your understanding of address blocks, subnet masks, and host capacity. Exercise 1 Choosing an Appropriate Subnet Mask You are adding a new server to each of the following subnets. Given the addresses of the existing computers on that subnet, determine which subnet mask you should assign the new server.