Mastering TCP/IP Part 2: Transport, Internet and Network Layer – CompTIA Security+ Lesson 6

Last time we looked at the application layer. Today we are going to look at the other layers of TCP/IP and how they help the application layer do its job.

Transport Layer

This layer is responsible to establish session and datagram communication services for the application layer. It uses mainly TCP and UDP.

TCP in short, provides a connection between hosts with sessions. The packets sent are synchronized on both hosts and the communication should be error-free but takes more time than UDP.

UDP on the other hand is faster, but less error-free. It doesn’t use sessions and the applications using it are responsible for acknowledging the correct reception of the data.

This video gives you a nice explanation:

Internet Layer

This layer accomplishes most of the work in establishing the ability to exchange information between hosts. It is responsible for routing, IP addressing, and packaging.


The following is a list of the three standard protocols on this layer:

Internet Protocol (IP)
  • Responsible for IP addressing
  • Fragments and reassembles message packets
  • Routes information, doesn’t verify it
  • Determines if a destination is known
  • Routes information to destination if known. If not it routes it to the router.
Address Resolution Protocol (ARP) Responsible for resolving IP addresses to Network Interface layer addresses (mostly MAC)
Internet Control Message Protocol (ICMP)  Provides maintenance and reporting functions (Ping uses it)

Network Access Layer

Places and removes packets on the physical network through communication with the network adapters in the host. This layer makes TCP/IP indipendent of the type of network topology. It can also communicate with more than one network topology at a time. So it can be used in any environement. Which makes the internet possible, I think.