About description of IP address assignment, which of the following is correct? (Multiple Choice)
A . Unless AnyCast is used, the IP address of the entire network must remain unique
B . IPv4 address space is divided into three categories: A, B, and C
C . When assigning addresses, if the /24 -bit mask length is used uniformly, the network design can be simplified
D . In order to improve the efficiency of the use of IP addresses, we generally use VLSM and determine the mask length as needed
Answer: AD