Thoughts on 'must memorize' knowledge?

I am curious to get this boards thoughts on relatively straightforward stuff that any IT professional should simply sit down and memorize or learn how to do, to either advance or just be generally well rounded. Off the top of my head:

Commonly used ports
OSI model (including what protocols are used at what layers)
Subnetting
Hexidecimal
Basics of common encryption protocols (Symmetric v. Assymetric, bit length, broken or not broken)
Basic Windows shell commands
Basic linux shell commands

Any others you would add?

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Comments

JaneDoe

Internal vs. external IP address and loopback addresses.

NotHackingYou

Location of hosts file in Windows.

paul78

IMO - understanding how to find information is probably one of the most valuable skills to have in IT - so I would list memorizing Google advance search operators.

DevilWAH

how to trouble shoot efficiently.

My head is full of information, but its knowing how to best apply it that important. The detail can always be filled in later, either from memory or on-line/documents.

If you concentrate on learning to be good at trouble shooting you will naturally find for your field what information is good to have in your head and what is good just to have a basic understanding that it exists. For example if you work in a 100% windows shop then there is no need to learn Linux. OK it might be useful for a new job, but you would be better learning windows in more depth than branch out in to Linux early on.

there is no definitive list that can be written, the best way to start is explore live system, and work out how they work, the more system you cover the more you will fine common knowledge between them, and as you get deeper in to a single filed the "common knowledge" becomes more in depth and specialised to that field.