An Subnet part that is used by internal routers within the organization to

An subnet part that is used by internal routers

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An Subnet part that is used by internal routers within the organization to deliver packets to a particular smaller Subnet. An IP Host part that identifies a particular individual device. TDC 594
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Subnetting Example Based on Subnet Requirements BrewCo was allocated IP address block 201.16.72.0/24 by their ISP. They have 6 departments and want to use 8 subnets internally. What Subnet Mask should they use? Initial subnet = 201.16.72.0 / 24 Initial prefix, subnet mask = /24 or 255.255.255.0 Size of initial subnet = 2 (32-24) = 2 8 = 256 IP addresses Number of new subnets = 8 = 2 3 New prefix length = 24 + 3 = / 27 New subnet mask = 255.255.255.224 Size of each new subnet = 2 (32-24-3) = 2 5 = 32 Result: Original block of 256 addresses is split into 8 subnets of 32 IP addresses each .
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Listing New Subnets Original subnet = 201.16.72.0/24 . Using mask 255.255.255.224, the 8 new subnets are: Subnet 201.16.72.0 /27 Valid host range = 201.16.72.1 – 201.16.72.30 Subnet broadcast address = 201.16.72.31 Subnet 201.16.72.32 /27 Valid host range = 201.16.72.33 – 201.16.72.62 Subnet broadcast address = 201.16.72.63 Subnet 201.16.72.64 /27 Valid host range = 201.16.72.65 – 201.16.72.94 Subnet broadcast address = 201.16.72.63 (… leaving four subnets out here …) Subnet 201.16.72.224 /27 Valid host range = 201.16.72.225 – 201.16.72.254 Subnet broadcast address = 201.16.72.255
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Determining the Subnet Mask Subnetting Based on Subnet or Host Requirements There are two considerations when planning subnets: Number of Subnets required Number of Host addresses required Formula to determine number of useable hosts 2 n -2 2 n (where n is the number the number of host bits remaining) is used to calculate the number of hosts -2 Subnetwork ID and broadcast address cannot be used on each subnet
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Subnetting Example Based on Host Requirements JoyCo Corp. has been allocated IP network 130.88.0.0/16 and is split into departments that may have up to 1000 computers each. How many equal-sized subnets can they create with at least 1000 valid host addresses in each? What subnet mask should they use? What are the resulting Subnet IDs? TDC 594
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JoyCo Example Subnet sizes must be powers of 2. The smallest power of 2 that is greater than 1000 is 2 10 = 1024. This would give them 1024 – 2 = 1022 valid host addresses in each subnet. Thus, each IP address needs 10 Host bits. The new prefix length will be 32 – 10 = / 22 . So, new Subnet mask is 255.255.252.0 . The difference between old prefix length (16) and new prefix length (22) is 22-16 = 6 , so 6 bits are borrowed: Number of new subnets = 2 6 = 64 subnets We also could have figured this as 65,536 / 1024 = 64 TDC 594
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Calculating JoyCo Subnets First Subnet ID will be the original network address with the new prefix length. First Subnet ID is 130.88.0.0 / 22 New Subnet Mask = 255.255.252.0 Two ways to calculate other subnet IDs: Start with first subnet ID and add 1024 IP addresses to it. This will increase value in 3 rd byte by 1024 / 256 = 4 .
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