A couple of questions on nat?

Question

linux

I have two questions related to nat here. I ask all "those who are not in the subject and slept in the lesson" to go through the forest. Interested in specifics.
1. Are the rules for traffic "all LAN go to the Internet via nat" equivalent (in terms of technical design) to the rules "LAN 1 goes to the Internet via nat" "LAN 2 goes to the Internet via nat" and so on
2. Srach on the second question we have already flashed. They seem to be smart people. and have not found an answer to it. Usually, providers have a range of gray IP addresses issued to the client, and through the real one all clients are pressed into the Internet. There is a second option one client - one real person. But then I met a couple of months another implementation. Many clients and all of them are assigned the same real person (pppoe). How?????? I will clarify. We look at the properties of the network connection and see the real one there. We go to a friend and see the same real person there !! What kind of crutch is heaped up here?

Answer 1

1. In general, they are equivalent. But it depends on what you want to get at the output :-)
2. Have you checked with such users, the IP address that they have on the interface - is it visible from the outside? :-) Or is there one white IP on the interface, and if you go to some 2ip.ru, then there will be a completely different address?
Technically, it can be implemented like this - the provider has several BRAS's, to which users connect via PPPeE. Within one BRAS, the addresses must be unique, and within the entire set of BRAS, they may coincide. This is how we do it, for example. Only not with white IPs, of course, but with gray ones. Why give white IPs to clients in this scheme, I don’t know. Each BRAS issues IP addresses to clients in the 10.0.0.0/16 range. Those. 1st brace can have a client with IP 10.0.0.1, and 2nd brace can have a client with the same IP address. But at the same time, two clients on the 1st BRAS cannot get IP 10.0.0.1, of course. Otherwise, routing will break.

Answer 2

I can say for sure that it is possible on the provider's side - to enable several sessions for one login-password pair. But for some reasons they don't give :)