Which of the following is a valid IP address for use on the Internet?

A.
239.168.11.21

B.
172.192.4.254

C.
56.144.226.123

D.
127.0.0.1

Explanation:
Internet hosts require public IP addresses. 56.144.226.123 is a public IP address and is thus valid
for use on the Internet.
Incorrect Answers:
A: 239.168.11.21 is a Class E IP address. This class is reserved.
B: 172.192.4.254 is a private IP address. Private IP addresses are used on private networks and
not on the Internet.
127.0.0.1 is a loopback address used to troubleshooting. It is not assigned to computers and
cannot be used on the Internet.Reference:David Groth and Toby Skandier, Network+ Study Guide
(4th Edition), Sybex, Alameda CA, 2005, pp. 125-126.