How does Router know where to forward packet
Problem
If several computers with local addresses (192.168.0.#) are connected to a router and each computer opens a web browser and requests a page over HTTP, when these TCP:80 packets are sent out, the router switches the local address with the static IP of the router (i.e. Provider given IP) so the server can reply to the appropriate address. But how does the router know to which computer to forward the HTTP reply, since the TCP header does not contain the local IP address (does it?), and all computers are using port 80? Does this have anything to do with the MAC addresses? How exactly does this work?
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1 Fix
Fix for: How does Router know where to forward packet
Most home routers use a special-case of NAT called PAT. You'll also see it referred to as NAPT, or IP Masquerading. All three of the latter terms mean the same thing in general use. (The acronyms - Network Address Translation / Port Address Translation / Network Address Port Translation) When the packet goes out from your internal machine, the source address is rewritten as you are aware. The source port is also changed, usually to a high number, and the router keeps an address translation tabl…
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