The method of creating classless IP addresses using variable-length subnet masks is known as:

• A. Classless Inter-Domain Routing (CIDR)
• B. Classful
• C. Network Address Translation (NAT)
• D. Subnetting

Answer: (A)

CIDR, or Classless Inter-Domain Routing, is the addressing method that allows classless IPs by using variable-length subnet masks. It drops the old classful A/B/C boundaries and lets networks be defined with any prefix length, written as a slash notation like 192.168.0.0/24 or 10.0.0.0/8. This flexibility makes address allocation much more efficient and enables route aggregation, where a single routing table entry can cover multiple subnets. NAT translates addresses between networks, not how IPs are allocated, and subnetting is the process of dividing a network into smaller pieces—part of CIDR’s capability, but the defining feature is the use of variable-length prefixes to create classless addresses.