Which IPv4 address range is reserved for loopback and what is a typical loopback address?

• A. 255.0.0.0/8; 127.0.0.1
• B. 127.0.0.0/8; 127.0.0.1
• C. 224.0.0.0/4; 127.0.0.1
• D. 127.0.0.0/8; 127.0.0.1

Answer: (B)

Loopback addresses are used to communicate with the local machine, staying entirely within the host rather than going out onto any network. In IPv4, the entire loopback range is 127.0.0.0/8, meaning any address from 127.0.0.0 to 127.255.255.255 will loop back to the same device. A typical loopback address is 127.0.0.1, which is the one most people use to test the local TCP/IP stack.

When you send a packet to 127.0.0.1, it never leaves your computer; the IP stack redirects it internally, making it ideal for testing applications and services without involving any network hardware. The other ranges listed correspond to different purposes (for example, 224.0.0.0/4 is multicast, and 255.0.0.0/8 is part of legacy broadcast addressing), so they are not used for loopback.