Routing localhost traffic to external IP address

If you just want to route a single port, then establish an ssh tunnel

ssh -N -n -L 443:localhost:443 192.168.100.50

You can setup ssh-keygen keys so you do not need to use a password.

Now you can use localhost:443 as long as the ssh tunnel is established.

ssh tunnels are secure. ssh tunnels can even tunnel across the internet as long as you can address the remote system. I actually use an ssh tunnel to VNC with my Mom's iMac 300 miles away. I tunnel port 5900 (the VNC port).

You also do not need to do 443 to 443, you can do any local port you like and have it sent to port 443 on the remote

ssh -N -n -L 12345:localhost:443 192.168.100.50

So localhost:12345 will be delivered to port 443 on host 192.168.100.50

Why? The hosts file is specifically for rerouting ip address traffic. Maybe I'm not understanding your issue, sorry. Adware and other malware often put redirects into the hosts file to redirect traffic.

IP doesn't work the way that you want and need here, and localhost is used all over the place within macOS and most other IP hosts. It's the IP address of "me" within IP networking, and lots of software uses that for internal connections rather than determining the local IP address and using that.

DO NOT CHANGE localhost. Ever! You will just break your Macs ability to do networking.

If the other machine is a Mac, then give it a simple name via System Preferences -> Sharing - Computer name. For example: "other". Then you can access that system using "other.local"

If the other system is not a Mac, then see if it has a way to give it a simple name, and then it should be available via "simplename.local" For example I've done this with my Synology NAS.

If you cannot give the other system a simple name that works with .local you can add a simple name to your /etc/hosts file (just DO NOT associate it with localhost)

192.168.100.50 simplename

And you can access that host via "simplename"

But as MrHoffman said, if you change localhost, you are going screw up your Mac.

"But as MrHoffman said, if you change localhost, you are going screw up your Mac."

Only if you don't do it right.

https://en.wikipedia.org/wiki/Hosts_(file)

I think BDAqua is correct about the port number but I can't remember for certain.

I'd look to use Parallels networking here, as that includes different configuration options for remapping the internal (emulated) network. Selecting bridged mode should put the Parallels guest onto the same network as the Mac, for instance. Alternate-clicking on the Parallels icon in the Dock should also bring up a networking selection where the port-forwarding can be configured.

I did some googling, _AND_ I have not tested this, but it might do what you want.

This webpage seems to explain what the curl --resolve option is doing

https://curl.haxx.se/libcurl/c/CURLOPT_RESOLVE.html

And this page skirts on the edge of explaining

https://support.acquia.com/hc/en-us/articles/360005257154-Use-cURL-s-resolve-option-to-pin-a-request-to-an-IP-address

The first URL says the DNS cache is populated with the host:port association you want, and then any app using DNS to lookup the address will get the curl --resolve DNS entry.

Or at least that is how I am interpreting those 2 webpages.

I just tried this at work, and it did not seem to do what I was thinking.

All it seemed to do was re-vector curl to the specified destination via localhost and fetch the webpage. Not what I was thinking, but totally in keeping with what curl does for a living.

If you just wanted to fetch a webpage from the other system via localhost, I guess it could work.

Maybe BDaqua can clarify if my experience is what he expected, or if he expects something else?

The ssh tunnel will intercept any app going to localhost:443

You showed Parallels. That’s commonly used on macOS, and folks do try to network from guests within.

Okay.

Backing up... Rather than a proposed and unworkable solution—the wholesale remapping localhost to else-host—can we back up a step here and learn more about the problem you are working to resolve here and what you are trying to do—that’s what, and not how you are trying to do it—and what software is involved? Some background and requirements? Again, I’m not looking for any proposed solutions here, but rather some more on the background and requirements here.

You can try using the hosts file.