Subnets 1 2 4 8 Hosts per Subnet 254 126 62 30 in .NET framework

Generator QR in .NET framework Subnets 1 2 4 8 Hosts per Subnet 254 126 62 30

Network Address 208.147.66.0/24 208.147.66.0/25 208.147.66.0/26 208.147.66.0/27

In situations such as these, you can use VLSMs to accommodate your specific network needs without having to acquire new address space from your ISP. When using VLSMs to divide your network into subnets of varying sizes, a specific pattern of subnet IDs with trailing 0s must be used, up to a maximum of seven subnets for a Class C network. These trailing 0s prevent the subnet address spaces from overlapping with each other. When the subnet IDs with VLSMs are fixed in the specific pattern shown in Table 2-6, subnets do not overlap, and addresses are interpreted unambiguously.

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Table 2-6

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

126 62 30 14 6 2 2 208.147.66.0.0/25 208.147.66.0.128/26 208.147.66.0.192/27 208.147.66.0.224/28 208.147.66.0.240/29 208.147.66.0.248/30 208.147.66.0.252/30

Figure 2-17 illustrates how you can use VLSMs to accommodate 3 subnets of 100, 50, and 20 hosts, respectively.

Subnet B: 50 computers Subnet ID: 10

Subnet A: 100 computers Subnet ID: 0

208.147.66.0.128/26

Subnet C: 20 computers Subnet ID: 110

208.147.66.0.192/27

208.147.66.0.0/24

Figure 2-17

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Maximizing Available Host IDs with VLSMs In Table 2-6, 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 7 subnets presented, you could define the all-1s subnet ID at any level in the table to replace all of the subnets listed below that subnet. For example, you could define a subnet ID of 1111 to replace subnets 5 through 7 listed in the table. Doing so would give you a second subnet of 14 hosts, instead of 3 subnets accommo dating a total of 10 hosts. This technique thus allows you to maximize the number of hosts your 5-subnet network can accommodate.

Tip If your Class C network contains 3, 5, 6, or 7 subnets, you can maximize the number of available host IDs in your network by using VLSMs.

In this practice, you use Calculator and the tips on pages 2-27 and 2-29 to determine the missing subnet information.

Assume your ISP has allocated you the network address 206.73.118.0/24. Using the requirement shown at the top of the table, complete the table by determining the num ber of bits required for the subnet ID or host ID, the number of bits left for the host ID or subnet ID, the network prefix version of the subnet mask, and then the dotted-dec imal version of the subnet mask.

Number of bits required for subnet ID Number of bits left for host ID Network prefix version of subnet mask Dotted-decimal version of subnet mask (Answer: 3) (Answer: 5) (Answer: /27) (Answer: 255.255.255.224)

Number of bits required for subnet ID Number of bits left for host ID Network prefix version of subnet mask Dotted-decimal version of subnet mask

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Number of bits required for subnet ID Number of bits left for host ID Network prefix version of subnet mask Dotted-decimal version of subnet mask

Number of bits required for host ID Number of bits left for subnet ID Network prefix version of subnet mask Dotted-decimal version of subnet mask

Determine the network class and default subnet mask for each network ID in the fol lowing table. Then use Calculator to determine the actual subnet mask configured for the address, the number of available subnets, and the number of available hosts per subnet.

Number of Configured Number of Available Subnet Mask Available Hosts per (Dotted-Decimal) Subnets Subnet

Network ID 207.209.68.0 /27 131.107.0.0 /20 10.0.0.0 /13 208.147.66.0/25