Iptables, ACLs, etc...?

Question

linux

I'm stuck, I'm at a dead end in front of the fence, over which I can't jump yet.
I am currently studying:

• firewall(netfilter) on linux,
  
• before access control list on cisco,
  
• and even before that Squid proxy, there is also acl.
  

I have porridge in my head. I ask you can put everything on the shelves for the novice nedoadminu.
How is this all different?
What, where, when, for what each of the options is used.

Answer 1

Firewall in the form of a cisco - for the organization of a predictably behaving (with normal settings) more or less fault-tolerant network, a spare parts kit or a service support contract is recommended. The same in the form of a server with Linux - for lovers of red-eyed or constrained in funds. A proxy is generally a higher level, since it refers to specific traffic transfer protocols.

Answer 2

ACL is just a convenient way to write access rules, each software brews them in its own way.

Answer 3

And what is the task? You have a bunch of horses here, people ...