Abstract:

In the last decade, or even longer, computer networking has been a field that cannot be overseen in technical and STEM education. While technological development and affordable prices brought powerful network devices to the end-user, all the networking principles are still based (and probably will remain so) on old protocols developed back in the 60's and the 70's of the twentieth century. Therefore, it can be expected that understanding the basics of networking principles is something that future engineers should be familiar with.

The global network of today, the Internet, is based on a TCP/IP stack of protocols. That is the fact that is not to be changed - the most important change that seems to be predictable will be wider acceptance and usage of a newer version of Internet Protocol (IP) - IPv6 increases its adoption in the global network but it is still under 30%. Even though different modifications of certain transport (TCP, UDP) and network (IP) protocols appeared, essentially the basics are still based on old protocols and most of the network traffic is still using the good old TCP/IP stack.

In order to explain the basic functional principles of todays networks, different kinds of case studies in real-networks or emulated environments can be introduced to students. Among those, one of the case studies we use in our education is related to explaining, the so called, IP fragmentation - the process that sometimes "automagically" appears in IP network protocol-based networks when certain constraints are met. The process of IP fragmentation in the "old" (but still dominant) IPv4 protocol used to influence main network nodes (routers) processing performances and was one of the processes that was completely redesigned in the newer, IPv6 protocol. Even though the IP fragmentation may not appear so frequently in networks of today (due to the convergence in edge-networks), the principles are worth explaining.

In this paper, details of the IP fragmentation in an emulated testbed network will be covered, explaining all the important issues and visualizing the fragmentation process. In order to show improvements that the IPv6 introduced, the same testbed network will be analyzed when using IPv6, showing the process of avoiding multiple fragmentation in the network. All the facts and functionalities will be referenced to valid standards. For generating network traffic (IP packets that will be sent to the network) plain old ping tool will be used, while the whole network will be emulated using IMUNES tool. The goal of the paper is to give an example on how such important, but quite basic, phenomena in the network could be explained and introduced to students.

Keywords:

TCP/IP, IMUNES, network, IP fragmentation, MTU, ping.