Need help to understand what's happening on TCP level when http proxy is used.
When client wants to open a website through a proxy, first connection is established between client and proxy. Then proxy just transfers the traffic between client and destination server in both ways. On HTTP level, server sees the exact same data that client sent (e.g. for HTTPS connection).
The question is: is it true for a lower TCP level? Does server receives the exact same TCP packets that were sent from client, or proxy server can rebuild them before passing to the destination server? Another way to question this: if client is a Windows machine with configured TTL=128, TCP window size=65535 and the proxy server is a Linux server with TTL=64 and window size=5840, what will the destination server see?