In the address 172.16.55.87 /20, what does the /20 indicate?
A . the subnet can accommodate 20 hosts per network
B . /20 is the prefix length: the first 20 bits are the network address; the remaining 12 bits are the host portion
C . this subnet is the 20th usable range
D . this IP address is the 20th usable IP in the range
Answer: B