it's all so ad-hoc and random. Firewalls have expensive and cheap operations...passing a packet? Cheap. Opening the packet and rewriting the header? Expensive.
That can be leveraged for evil.
How do you even organize that kind of random trivia?
That can be leveraged for evil.
How do you even organize that kind of random trivia?
Having been slowed down in the past by this kind of thinking: My advice is don't.
You throw the information together and forget about organization (as in a final presentable organization), you just write. Use systems like tags (metadata) to attach concepts and use queries on the tags to find related things. As you build up the knowledge base you can start organizing it more properly, into real essays or chapters and sections. Not all knowledge is amenable to pre-organization before you begin working, and even if you try to have some initial organization as you start writing you will find missing details and then have to fit them in.
As for organization, I just dump everything I learn in a markdown file on that topic, then look for structure later. So I would just open a file, call it `firewalls.md` and write that down in there. You can accrete a lot of written knowledge over time this way.
Imagine two companies merging. They both used 10.100.0.0/16. If you were in one of the companies wouldn't it be nice if the other re-ip'd?
... Guess what.. they won't and you don't want to. So you make a box, that turns your ips into 10.101.0.0/16 and theirs into 10.102.0.0/16... and you leave your IPs alone :).
Yeah, some things won't work across that bridge. But it'll get you started.
Firewalls can do really, really evil stuff. DNS? Yeah, we'll answer ALL dns queries.. Even ones you send to 8.8.8.8, or 1.1.1.1...
The BOFH playbook is large, and varied. :)
There's a TTL or Time To Live value to make packets eventually die, otherwise, packets could potentially move from router to router forever. So at a minimum, your firewall, or router, rewrites the header to Decrement the TTL by one with every hop.
Which spawns a really interesting thought experiment that results in the creation of the traceroute utility.
Take a look at Julia Evans’ writing for inspiration.
Also, https://rachelbythebay.com/w/
Providing the real life scenario makes the reference memorable - the human brain is set to remember things that matter and discard things that don’t. A story establishes the usefulness of the things.
Take a look at Julia Evans’ writing for inspiration.