One understanding that I think has helped me a great deal in troubleshooting problems, and designing networks and services is the evolution of a network packet as it transverses different pieces of network hardware. Today I will try to cover at a high level, the packet creation process, switching to the local Vlan, packet routing, NATing and firewalls, and VPN IPSEC encapsulation. During this discussion we will track the changes to a network packet in the IP and TCP/UDP headers.
This will be a multipart article and we will start by going over some prerequisites for understanding. This article is written to server admins, and so a deep technical knowledge is not required. If you understand the basics of server administration and the data contained in the prerequisite section I believe you will be able to comprehend, and find this article helpful.