Question

Suppose Host A sends Host B a TCP segment encapsulated in an IP datagram. When Host B receives the datagram, how does the network layer in Host B know it should pass the segment (that is, the payload of the datagram) to TCP rather than to UDP or to some other upper-layer protocol?

Answer 1

The 8-bit protocol field in the IP datagram contains information about which transport layer protocol the destination host should pass the segment to.

Step-by-step explanation:

If host A sends a message to host B a TCP segment encapsulated in an IP datagram, for the network layer in Host B to know which transport layer protocol to pass the segment to, there is always an 8-bit protocol field available in the IP datagram with the necessary information of which of the transport layer protocol that the segment should be passed to by the destination host.