> | Lab Activity 9.2.1: Creating subnets The table shows an example, which is covered in this activity.
> Host IP Address | Class | Subnet Mask | No. of Subnet Bits | Maximum # of Subnets s = s n – 2 | Ordinal Number of this Subnet
> 138.101.114.250 |  | 255.255.255.192 |  |  |
> Subnet Address of This Subnet or Wire | Range of Host Addresses For this subnet | Broadcast Address of This Subnet
> Step 1: Translate Host IP Address and Subnet Mask into binary notation.
> | 138. | 101. | 114. | 250
> IP Address | 10001010 | 01100101 | 01110010 | 11111010
> Mask | 11111111 | 11111111 | 11111111 | 11000000
> | 255. | 255. | 255. | 192
Step 2: Determine the Network (or Subnet) where this Host address lives: Draw a line under the mask Perform a bit-wise AND operation on the IP Address and the Subnet Mask Note: 1 AND 1 results in a 1, 0 AND anything results in a 0 Express the result in Dotted Decimal Notation The result is the Subnet Address of this Subnet or "Wire" which is 138.101.114.192
| 138. | 101. | 114. | 250
# IP Address | 10001010 | 01100101 | 01110010 | 11111010
Mask | 11111111 | 11111111 | 11111111 | 11000000
# Network | 10001010 | 01100101 | 01110010 | 11000000
| 138 | 101 | 114 | 192
> Step 3: Determine which bits in the address contain Network information and which contain Host information: Draw the "Great Divide" (G.D) as a wavy line where the 1's in the Default Subnet Mask would end for this class address (if no subnetting occurred). In our example, the IP Address is a Class B address, and so the Default Subnet Mask is 255.255.0.0. Draw the "Small Divide" (S.D.) as a straight line where the 1's in the given mask actually end. The network information ends where the 1's in the mask end The result is the "Number of Subnet Bits" may be determined by simply counting the number of bits between the G.D. and S.D., which in this case is 10 bits. Step 4: Determine bit ranges that are for subnets and for hosts: Label the "subnet counting range" between the G.D. and the S.D. (these are the bits that are being incremented to make the subnet numbers or addresses). Label the "host counting range" between the S.D. and all of the way to the end on the right (these are the bits that are being incremented to make the host numbers or addresses). Step 5: Determine the range of host addresses available on this subnet, and the broadcast address on this subnet: Copy down all of the network/subnet bits of the Network Address (i.e. all bits before the S.D.) In the host portion (to the right of the S.D.) make the host bits all 0's except for the right most bit (or least significant bit), which you make a 1. This gives you the first Host IP Address on this subnet, which is the first part of the result for "Range of Host Addresses for This Subnet," or in our example 138.101.114.193. Now, in the host portion (to the right of the S.D.) make the host bits all 1's except for the right most bit (or least significant bit), which you make a 0. This gives you the last Host IP Address on this subnet, which is the last part of the result for "Range of Host Addresses for This Subnet," or in our example 138.101.114.254. In the host portion (to the right of the S.D.) make the host bits all 1's. This gives you the Broadcast IP Address on this subnet. This is the result for "Broadcast Address of This Subnet," or in our example 138.101.114.255. Step 6: Determine the maximum number of subnets and usable subnets: The maximum number of subnets is determined by how many bits are in the subnet counting range (in this example, 10 bits). Two methods: Exponents Use the formula 2n - 2, where n is the number of bits borrowed form the host field. 210 = 1024. Subtract 2 for the number of usable subnets. 1024 - 2 = 1022 Charting
> 1024 | 512 | 256 | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1
> 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1
> > Make 10 columns for the 10 subnet bits Convert from binary to decimal. This produces the mask address. 1023 in our example. Subtract 2 for the number of usable subnets Put the result in "Maximum # of Subnets s = sn - 2," where n is the total number of subnets and s is the number of usable subnets. In our example 1022 = (1024 - 2) Step 7: Determine the ordinal number of this subnets (i.e. which one of this subnet, out of the maximum number of subnets available: Write down all of the bits in the subnet counting range (i.e. between the G.D. and the S.D). Convert this number to decimal. 0111001011 = 459 Or use the chart
> > 1024 | 512 | 256 | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1
> > | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 0 | 1 | 1
256 + 128 + 64 + 8 + 2 + 1 = 459 This is the result for the "Number of This Subnet," which is the 459th subnet