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How does an incoming SSH connection request to a public IP a

[ Edited ]

Let's say I have two machines mA (Private ip: and mB (Private ip: within the same LAN whos public IP address is These machines both have users with common username root. Additionally, mA has user uA and mB has user uB.

I understand how ssh communication from mA or mB to another public IP works. SSH from mA port 22 creates a NAT table in the router which corresponds to port 22 as source address. So any incoming reply from ssh requests from to port 22 can be reverse translated to mA port 22. This is possible because of the existence of NAT table entry for mA.

Now, if any other server outside the LAN tries to ssh to mB using ssh root@ How does the router know which machine in the LAN to send this SSH request? (Since there is nothing to identify mB in NAT table now. And both mA and mB have root).

Is it different from what happens when you try to ssh uB@ where user uB only exists in mB?


Re: How does an incoming SSH connection request to a public


This question is an exact copy from where the answer is also given.


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