General questions about the Internet and networks?

Question

Computer networks

Perhaps this is not entirely correct, but there are several small questions (and rather stupid ones)), so I decided to combine them into one topic: subparagraphs so that it would be possible to answer briefly to each of them)
1) Is the domain of the site and the domain of the organization (for example, an enterprise / educational institution managed, for example, Active Directory) - is it the same thing?
1.1. For example, is there a domain name, website domain and organization domain - are they different things? For example, with a domain organization, everything is more or less clear - for example, AD - allows you to manage a fleet of machines using group policies if the machine is part of a domain, for example, on a local network.
1.2. Can a machine be controlled by a domain while on another network and communicate with the domain controller on the first network? 1.3.A domain name is, in fact, a record in the DNS tables? after all, the site can be without a domain name?
1.4.If the site is hosted on a server of organization X with its own domain, does this affect its domain name or is it separately configured in DNS?
1.5. Do the concepts of "domain" intersect at all - in the sense of management (for example, AD) and the site domain (not a domain name - that is, what does the site domain mean - that it belongs to the machine park of organization X?)
2) I just can’t figure out how masks work for subnets:
For example, if the main gateway (gateway) has the address 192.168.100.2 , and the machine is assigned a static IP (of course, the DHCP network, but let's take it for an abstract example) - 192.168.90.10 - what should be the mask and why? Well, i.e. , conventionally, if the machine and the network device have the same addresses 192.168.x.x and 192.168.x.x - the mask will be 255.255.0.0 - where because to me x - 0 - will mean the whole range - i.e. 255 address spaces of 255 addresses (well, 0 and 256 are reserved, over). Here, using the addresses 192.168.100.2 and 192.168.90.10 as an example, it turns out that the 90.x subnet is more than 100.x, isn't it? and how can a gateway be in a smaller subnet (by 10) it issues a network?
3) From problem 2 - are there any exercises / lessons to get a hand in network design in theoretical terms? I mean, for example, not Cisco Packet Tracer - it's more of a network design tool / simulator. Rather, I need a manual about the calculation of networks (not even a manual, but a simulator / practical tasks), their nesting, interaction. Of course, I read about class and classless addressing, but the puzzle is not going in my head.
4) Active Directory - developed by MS and, as I understand it, is in fact the de facto standard for Windows machines?
4.1. What are the analogues?
4.2.Is there something like the OSI standard - from the world of management and domain building - how OSI is a more abstract standard against which other technology stacks can be evaluated, for example TCP\IP
4.3 Purely in theory, you can write your own domain management system (or another hierarchical structure of the fleet of machines) or are these purely proprietary concepts and what can you read about it?

Answer 1

1)
1.1 By principle - yes. Only for the site, a generally known domain is used (purchased), and in theory everyone can get access to it (if you make a website, for example), and for AD, you can use any invented domain, tk. it usually does not go further than your local network.
1.2 In principle, yes, with the correct network settings, but no one does that. Unless inside VPN
1.3 Yes, this is an entry in DNS. The site does not need a domain name to work. This is done for the convenience of users
1.4 This can be configured separately, no, it does not affect. These are generally different things \ services
1.5 Usually not (99%)
2)
So they will be routed based on the network 192.168.x.x and in order for them to see each other there must be a mask of 255.255.0.0
The logic here is this - the mask 255.255.255.0 limits the network to 254 possible (active) addresses. With a mask of 255.255.0.0, there can already be 65534 active addresses ... With a mask of /24, only the last "cell" is active. With a mask of /16, the last two
For your example, if I look correctly, /18 of the mask 255.255.192.0 is enough

spoiler

Адрес : 192.168.90.10 11000000.10101000.01 011010.00001010
Маска : 255.255.192.0 (18) 11111111.11111111.11 000000.00000000
Wildcard: 0.0.63.255 00000000.00000000.00 111111.11111111
Сеть : 192.168.64.0/18 11000000.10101000.01 000000.00000000
Хост(min): 192.168.64.1 11000000.10101000.01 000000.00000001
Хост(max): 192.168.127.254 11000000.10101000.01 111111.11111110
Broadcast: 192.168.127.255 11000000.10101000.01 111111.11111111
Хостов в сети: 16382 класс C, Интранет

https://www.ispreview.ru/ipcalc.html
3) No idea. I learned to "find"
4) Yes
4.1 Yes, there is essentially one analogue - Samba (Linux)
Judging by the habr, the list is as follows - FreeIPA, Samba4, UCS, OpenLDAP, 389 Directory Server
4.2 No idea
4.3 You can, study the above software, see what it can do. But why?