What is the fundamental difference between NAT and PROXY?

Question

Computer networks

Here I read and read, and I can not understand what is the difference between technologies. I imagine how nat works, it takes a conditional 1 external address, takes a bunch of local ones, passing from the local to the external one, changes the IP source and port to its external one, writes it to the table and lets it in, then turns the answers back against the table and here we have the Internet. But how the proxy works and I can not understand. They say it becomes a full-fledged intermediary, but any nat with a masquerade becomes a full-fledged intermediary, as for me. Tell me, please, or poke your nose into the link where it is written more intelligibly (
Everywhere they write and talk about open proxies and how cool they are, there is no principle of operation of the technology.

Answer 1

The neighbor asked you to call the gas service. You are a proxy for a neighbor.
Several neighbors have asked you to call the gas service. You called at the first request, and the others answered that you had already called. You are a caching proxy for neighbors.
The neighbor took your phone and called the gas service from your number. You are NAT for a neighbor.

Answer 2

A proxy, unlike NAT, establishes a second connection on its own behalf, unloads data from the server and sends it to the client via a local connection. And in general, a proxy server is a software and hardware complex, and NAT is a network technology.

Answer 3

The fundamental difference is in the level of abstraction.
Nat "on the fly" changes the ip address field in packets passing through the device.
Proxy establishes a connection with the client, and then, on behalf of itself, broadcasts client requests to the outgoing network (for example, to the Internet), although there are transparent proxies.
From this follows the following.
Nat technology is a relatively easy solution, however, it can only do one thing - change ip addresses.
A proxy is already a program, and the variability of what it does with traffic is much greater. It can cache requests, it can monitor the list of white sites, and compare this list with AD users, and calculate the amount of traffic allowed. In general, this is already a service. This comes at a price, in terms of computing resources.
UPD. The actual scope of these technologies is different.
Nat is used as a networking tool, to save an address plan, hide addresses, organize piping.
Proxy is a service for end users, servers for organizing access to any resources.

Answer 4

I’ll add a little bit @vvpoloskin
NAT is when you sit in the yard, you smell gas and shout “call the gas service”. one of the neighbors calls, naturally a set of questions about the situation comes from the gas workers, which the neighbor voices to you through the window and retells your answers into the phone :) the
computer in the local network has the address 192.168.1.100. it is local and does not have the right to surf the Internet.
you want to go to the Yandex page. based on your desires, the browser generates a data request packet (in theory, an http channel, but we will omit the details) from your 192.168.1.100 to the Yandex server IP address and sends it to the network.
a router located on the border of the local network and the Internet catches a packet whose recipient is on the Internet and forwards it from LAN to the Internet.
but because the source address of the packet 192.168.1.100 does not have the right to be on the Internet, it is replaced by the Internet address of the router, this is source NAT (one of the options for Network Address Translation - network address translation) - substitution of the sender address.
and also a temporary rule is created so that the response packets from Yandex are sent to you (this is how the Yandex servers are completely sure that they communicate with the Internet address of the router and send data packets to this ip). it will already be destination NAT - substitution of the recipient's address.
a lot of things are omitted and not described, but I tried to convey the essence in a simpler way.