Which of the following protocols uses IP protocol number 88?

The correct answer is EIGRP, which uses IP protocol number 88. Enhanced Interior Gateway Routing Protocol (EIGRP) is a distance vector routing protocol that incorporates features of link-state routing protocols. It was designed by Cisco to efficiently manage IP routing within larger networks and is classified as an advanced distance vector protocol, utilizing both metrics for choosing the best routes and maintaining routing tables.

Assigning a unique protocol number helps the Internet Protocol stack identify the packet type being transmitted, allowing proper delivery and processing. EIGRP's unique protocol number distinguishes it from other routing protocols, ensuring that the data is handled correctly by routers that support it.

In contrast, other options refer to different protocols: TCP is associated with protocol number 6; ICMP has protocol number 1; and OSPF, which is a link-state routing protocol, uses protocol number 89. Each of these protocols has its specific purpose and operates under different functionalities within the TCP/IP model.