Which term describes IP addressing that uses fixed default subnet masks per class?

Which term describes IP addressing that uses fixed default subnet masks per class?

• A. Classful
• B. CIDR
• C. NAT
• D. VPN

Answer: (A)

Classful IP addressing uses fixed default subnet masks defined by the address class. In this scheme, the class of an IP address determines the network portion length: class A uses 255.0.0.0, class B uses 255.255.0.0, and class C uses 255.255.255.0. Because these masks are fixed, the network is identified from the address itself without carrying a separate subnet mask in routing updates. This contrasts with classless addressing, where any subnet mask length can be used and must be advertised in routing. NAT and VPN are unrelated to this addressing approach—they serve different purposes (translation and secure tunneling, respectively).

Classful IP addressing uses fixed default subnet masks defined by the address class. In this scheme, the class of an IP address determines the network portion length: class A uses 255.0.0.0, class B uses 255.255.0.0, and class C uses 255.255.255.0. Because these masks are fixed, the network is identified from the address itself without carrying a separate subnet mask in routing updates. This contrasts with classless addressing, where any subnet mask length can be used and must be advertised in routing. NAT and VPN are unrelated to this addressing approach—they serve different purposes (translation and secure tunneling, respectively).