Hello,

The IP header is a Layer 3 header where you will specify the

source/destination IP addresses. You will also specify the upper layer

protocol that the network layer should communicate with for that specific

packet. This information is embedded in the packet using "protocol" field.

In the layer 4 header (TCP/UDP), you will specify the port information.

http://www.tcpipguide.com/free/t_IPDatagramGeneralFormat.htm

There are lot of layer 4 protocols that are not dependent upon the TCP/UDP

stacks. They directly interact with the IP layer and have their own way of

encapsulating the packet.

Essentially, you can look at entire TCP/IP stack as a way of packaging data

within a packet.

Hope this helps.

Regards,

NT