I don't know what is the exact usefulness of redis and what kind of problem it tries to solve.
I need to remember what exactly is NAT, what it does and how it works.
I need to understand, at least in general, how a Virtual Private Network works.
What the nslookup command does?
OK, it "shows the DNS config", but I want the details. I want to be able to explain it like using the Feynman Technique.
[Note: I remember the "TCP/IP Illustrated" book explains it very well and with practical examples.]
Explain how exactly SSH public and private keys work? (the concpets)
What exactly is LDAP?
How TLS/SSL certificates work?
possibly useful reading: https://www.digitalocean.com/community/tutorials/a-comparison-of-let-s-encrypt-commercial-and-private-certificate-authorities-and-self-signed-ssl-certificates