<P> The first class, designated as Class A, contained all addresses in which the most significant bit is zero . The network number for this class is given by the next 7 bits, therefore accommodating 128 networks in total, including the zero network, and including the IP networks already allocated . A Class B network was a network in which all addresses had the two most - significant bits set to 1 and 0 respectively . For these networks, the network address was given by the next 14 bits of the address, thus leaving 16 bits for numbering host on the network for a total of 65 536 addresses per network . Class C was defined with the 3 high - order bits set to 1, 1, and 0, and designating the next 21 bits to number the networks, leaving each network with 256 local addresses . </P> <P> The leading bit sequence 111 designated an at - the - time unspecified addressing mode ("escape to extended addressing mode"), which was later subdivided as Class D (1110) for multicast addressing, while leaving as reserved for future use the 1111 block designated as Class E . </P> <Table> <Tr> <Th> Class </Th> <Th> Leading bits </Th> <Th> Size of network number bit field </Th> <Th> Size of rest bit field </Th> <Th> Number of networks </Th> <Th> Addresses per network </Th> <Th> Total addresses in class </Th> <Th> Start address </Th> <Th> End address </Th> <Th> Default subnet mask in dot - decimal notation </Th> <Th> CIDR notation </Th> </Tr> <Tr> <Td> Class A </Td> <Td> 0 </Td> <Td> 8 </Td> <Td> 24 </Td> <Td> 128 (2) </Td> <Td> 16,777,216 (2) </Td> <Td> 2,147,483,648 (2) </Td> <Td> 0.0. 0.0 </Td> <Td> 127.0. 0.0 </Td> <Td> 255.0. 0.0 </Td> <Td> / 8 </Td> </Tr> <Tr> <Td> Class B </Td> <Td> 10 </Td> <Td> 16 </Td> <Td> 16 </Td> <Td> 16,384 (2) </Td> <Td> 65,536 (2) </Td> <Td> 1,073,741,824 (2) </Td> <Td> 128.0. 0.0 </Td> <Td> 191.255. 0.0 </Td> <Td> 255.255. 0.0 </Td> <Td> / 16 </Td> </Tr> <Tr> <Td> Class C </Td> <Td> 110 </Td> <Td> 24 </Td> <Td> 8 </Td> <Td> 2,097,152 (2) </Td> <Td> 256 (2) </Td> <Td> 536,870,912 (2) </Td> <Td> 192.0. 0.0 </Td> <Td> 223.255. 255.0 </Td> <Td> 255.255. 255.0 </Td> <Td> / 24 </Td> </Tr> <Tr> <Td> Class D (multicast) </Td> <Td> 1110 </Td> <Td> not defined </Td> <Td> not defined </Td> <Td> not defined </Td> <Td> not defined </Td> <Td> 268,435,456 (2) </Td> <Td> 224.0. 0.0 </Td> <Td> 239.255. 255.255 </Td> <Td> not defined </Td> <Td> not defined </Td> </Tr> <Tr> <Td> Class E (reserved) </Td> <Td> 1111 </Td> <Td> not defined </Td> <Td> not defined </Td> <Td> not defined </Td> <Td> not defined </Td> <Td> 268,435,456 (2) </Td> <Td> 240.0. 0.0 </Td> <Td> 255.255. 255.255 </Td> <Td> not defined </Td> <Td> not defined </Td> </Tr> </Table> <Tr> <Th> Class </Th> <Th> Leading bits </Th> <Th> Size of network number bit field </Th> <Th> Size of rest bit field </Th> <Th> Number of networks </Th> <Th> Addresses per network </Th> <Th> Total addresses in class </Th> <Th> Start address </Th> <Th> End address </Th> <Th> Default subnet mask in dot - decimal notation </Th> <Th> CIDR notation </Th> </Tr>

What is the default mask for a class b address in cidr notation
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