Earlier today on Twitter, I asked:
What networking concept do you wish you could go back in time and explain to your newbie self?
I received some interesting responses, ranging from understanding what purpose the OSI model serves to RIB versus FIB, from spanning tree to VRFs. Having taught a number of CCNA classes and been in a position to gauge student reactions, some of the responses were predictable. Others, like Bill's comment about not understanding the benefit of the OSI model, were intriguing.
I think that many of the knowledge gaps common in our field can be traced to a phenomenon in professional education where concepts are not thoroughly explained simply because the explainer has forgotten having learned them. An author of a book on spanning tree, for example, may be intimately familiar with the operaton of the protocol, and explain in numbing detail the root bridge election process, but fail to explain why a root bridge is necessary. I thought it would be an interesting exercise to take a casual poll along readers and see what other fundamental knowledge is commonly not well understood until one is several years into his or her career.
Back to the question at hand: For me, I think it would be IPsec. Not that I truly understand how it all works under the hood still today, but learning about IKE and ISAKMP and phase one and phase two early on was harsh. What about you?