| Remember that although a Class C address has a prefix of /24, not all addresses with a /24 prefix are Class C addresses. A Class C address is a classful address that has been obtained from the IANA. It is interesting that although the first guess is that two are better than one, two Class C addresses do not really improve the situation. The need to address 12 buildings requires 4 bits, which would allow only 14 hosts in each building. The network could be addressed with two Class C addresses if 14 hosts in each building are all that is required. There is very little growth allowance in this scheme, making it inadvisable. The most efficient addressing scheme with Class C addresses would be to use 40 Class C addresses. Consider, for example, the addressing scheme using Class C addresses. A Class C address would be allocated to each building. This would allow 254 hosts in each building and subnetting to the floor, if necessary. The other three Class C addresses would be used with VLSM to identify the regions and campuses. Table 3-7 shows the addressing scheme for the one Class C address to address one region, three campuses, and four buildings. Each region or state will now advertise five networksthe four Class C addresses for the buildings and the shared network for the state. One Class C network can be used for the state if the connections are point to point. Because there are 15 connectionsfour buildings per region, and three regionsthis means 12 connections to the buildings, plus three connections to the state. A Class C address would easily accommodate this, even with redundant connections built into the design. The reason that 40 Class C networks are needed is that the analysis of the state must be extrapolated to the entire organization. The organization covers three states, each with three regions, and each region has four buildings. Although the addressing described previously is correct, it would need to be extended to the other regions. This is calculated as follows: The number of buildings requiring Class C networks in three states, each with three regions, and each region in turn with four buildings is 3 * 3 * 4 = 36. Add to the three states requiring Class C networks the additional network required for the core cloud that connects the states, and you have 36 + 3 + 1 = 40. In total, therefore, 40 Class C networks will be required. Other than for academic interest in torturous addressing, this scenario would be an excellent candidate for a private Class B address. Table 3-7. The Class C Used to Identify the Campuses for Each Region | Entire Address in Decimal | Fourth Octet in Binary | Prefix Mask | | Region: Arizona | | 210.10.32.0 | | | | Campuses | | 210.10.32.32 | 001 00000 | /27 | | 210.10.32.64 | 010 00000 | /27 | | 210.10.32.96 | 011 00000 | /27 | | Buildings | | Tucson | | 210.10.32.36 | 001001 00 | /30 | | 210.10.32.40 | 001010 00 | /30 | | 210.10.32.44 | 001011 00 | /30 | | 210.10.32.48 | 001100 00 | /30 | | Flagstaff | | 210.10.32.68 | 010001 00 | /30 | | 210.10.32.72 | 010010 00 | /30 | | 210.10.32.76 | 010011 00 | /30 | | 210.10.32.80 | 010100 00 | /30 | | Phoenix | | 210.10.32.100 | 011001 00 | /30 | | 210.10.32.104 | 011010 00 | /30 | | 210.10.32.108 | 011011 00 | /30 | | 210.10.32.112 | 011100 00 | /30 | Table 3-8 shows how to address the departments or floors within each building. For this discussion, use 210.10.64.0 as the example Class C address. Four bits taken in the fourth octet allows 14 networks, either distributed between the floors or between departments, with 14 hosts on each subnet. Table 3-8. How to Address a Building Using a Class C Network Address | Entire Address in Decimal | Fourth Octet in Binary | Prefix Mask | | 210.10.64.16 | 0001 0000 | /28 | | 210.10.64.32 | 0010 0000 | /28 | | 210.10.64.48 | 0011 0000 | /28 | | 210.10.64.64 | 0100 0000 | /28 | | 210.10.64.80 | 0101 0000 | /28 | | 210.10.64.96 | 0110 0000 | /28 | | 210.10.64.112 | 0111 0000 | /28 | | 210.10.64.128 | 1000 0000 | /28 | | 210.10.64.144 | 1001 0000 | /28 | | 210.10.64.160 | 1010 0000 | /28 | | 210.10.64.176 | 1011 0000 | /28 | | 210.10.64.192 | 1100 0000 | /28 | | 210.10.64.208 | 1101 0000 | /28 | | 210.10.64.224 | 1110 0000 | /28 | | 