Which of the following uses classless subnet masks across a network?

A.
Subnetting

B.
CIDR

C.
Supernetting

D.
Summarization

Explanation:
Classless Inter-Domain Routing is based on variable-length subnet masking (VLSM), which allows
a network to be divided into variously sized subnets, providing the opportunity to size a network
more appropriately for local needs and also CIDR allows an address or routing prefix to be written
with a suffix indicating the number of bits of the prefix, such as 192.168.2.0/24.