Which protocol is defined as IP protocol number 6?

The protocol defined as IP protocol number 6 is TCP, which stands for Transmission Control Protocol. TCP is a fundamental transport layer protocol in the Internet Protocol Suite, and it is responsible for providing reliable, ordered, and error-checked delivery of data between applications running on hosts communicating over an IP network.

TCP achieves reliability through mechanisms such as error detection, retransmission of lost packets, and flow control. This makes it suitable for applications where data integrity and order are critical, such as web browsing, email, and file transfers.

The assignment of protocol numbers helps distinguish the different types of protocols used over IP, and TCP's designation as number 6 signifies its specific role and functionality within the broader landscape of network communication protocols. Understanding the properties and operation of TCP is essential for comprehending how data is transmitted reliably across networks.