UDP

For UDP protocol, the maximum length of the entire packet is 65535 bytes, and the payload length is 65535-20=65515 bytes.

TCP

For TCP protocol, the maximum length of the entire packet is determined by the Maximum Segment Size (MSS). MSS is the maximum data segment that a TCP packet can transmit each time. To achieve optimal transmission performance, the TCP protocol usually negotiates the MSS value between both parties when establishing a connection. When implementing the TCP protocol, the MTU value is often used as a substitute (minus the size of the IP packet header of 20 bytes and the TCP segment header of 20 bytes), so the MSS is often 1460 bytes. The communicating parties will determine the maximum MSS value for this connection based on the smaller of the two MSS values provided.

IP

For IP protocol, the size of the IP packet is determined by the MTU (Maximum Transmission Unit).