Appendix E. Solutions to Configuration Exercises
If the first four bits of a class D address are 1110, the lowest first octet is 11100000 and the highest first octet is 11101111. In decimal these two numbers are 224 and 239, respectively. Therefore, the first octet of a class D address will range from 224 to 239.
(a) Enough subnet bits n are needed so that 2n – 2 > = 16,000. There must be enough host bits h remaining so that 2h – 2 > = 700. A subnet mask of 255.255.252.0 provides 16,382 subnets of the class A address, and 1022 host addresses on each subnet. This mask is the only one that works. If one more bit is used for subnetting (255.255.254.0), there will not be enough host addresses. If one less bit is used for subnetting (255.255.248.0), ...