Understanding IP Addressing B-3Class A networks have a small number of possible networknumbers, but a large number of possible host numbers. Conversely,Class C networks have a small number of possible host numbers,but a large number of possible network numbers. Thus, the InterNICassigns Class A addresses to large organizations that have verylarge numbers of IP hosts, while smaller organizations, with fewerhosts, get Class B or Class C addresses. You can tell the variousclasses apart by the value of the first (or high-order) byte. Class Anetworks use values from 1 to 127, Class B networks use valuesfrom 128 to 191, and Class C networks use values from 192 to223. The following table summarizes some of the differencesbetween Class A, B, and C networks.Subnets and subnet masksOften an entire organization is assigned only one IP networknumber. If the organization has several IP networks connectedtogether with IP routers, the network manager can use subnetting todistinguish between these networks, even though they all use thesame network number. Each physical network becomes a subnetwith a unique subnet number.Subnet numbers appear within IP addresses, along with networknumbers and host numbers. Since an IP address is always 32 bitslong, using subnet numbers means either the network number orthe host numbers must use fewer bits, in order to leave room forClass First byteNumber ofnetworkspossible perclassNumber ofhostspossible pernetworkFormat of address(without subnetting) ExampleA 1-127 127 16,777,214 net.host.host.host 97.3.14.250B 128-191 16,384 65,534 net.net.host.host 140.100.10.11C 192-223 2,097,152 254 net.net.net.host 197.204.13.7
