What is the IP protocol number for TCP?

What is the IP protocol number for TCP?

• A. 4
• B. 5
• C. 6
• D. 17

Answer: (C)

In IP, the Protocol field in the IP header tells the receiver which transport-layer protocol should handle the payload. TCP, the reliable connection-oriented transport protocol, is assigned the value 6 in that field. So when you see 6 in the Protocol field, it means the payload is TCP. For reference, UDP is 17 and ICMP is 1, with the numbers defined by the IANA protocol registry. There are also other values for special cases like IP-in-IP encapsulation (value 4). This is why 6 is the number associated with TCP.

In IP, the Protocol field in the IP header tells the receiver which transport-layer protocol should handle the payload. TCP, the reliable connection-oriented transport protocol, is assigned the value 6 in that field. So when you see 6 in the Protocol field, it means the payload is TCP. For reference, UDP is 17 and ICMP is 1, with the numbers defined by the IANA protocol registry. There are also other values for special cases like IP-in-IP encapsulation (value 4). This is why 6 is the number associated with TCP.