I got it working on my Mac that has an Airport Extreme router. Here's how I did the port forwarding: I used Lighthouse (
http://codelaide.com/blog/products/lighthouse)!
Lighthouse costs $12.99. That's in addition to the donation you make for Subsonic so it will remember your web address. (I donated 20 euros, which is a little over $25.)
I also got the iSub app for my iPhone for $4.99.
Lighthouse installs as an icon in your Mac's menu bar, under which you select Edit Port Mapping Profiles ...
That brings up a window in which you click + to add a profile to the list in the top part of the window. I called my new profile "Subsonic." I then selected it in the top part of the window and in the bottom part of the window I clicked + to add the details I wanted: public port = 4040; private port = 4040; type = TCP. Then I turned on the check mark for "Enable this profile," and I clicked the Start Profile button.
Doing so allows the Mac to support port forwarding for port 4040, which is the port that Subsonic's server application, running on the Mac, uses by default. (The Subsonic application has to be running on the Mac for this server to even exist.)
Note that using this Lighthouse method avoids my having to configure my AirPort Extreme router in any special way to permit port forwarding. There was no need to use AirPort Utility at all.
Note also that Subsonic's Network Settings page, as it appears in my web browser, does not confirm -- repeat, does
not confirm -- that "Automatically configure your router to allow incoming connections to Subsonic (UPnP port forwarding)" is working. It instead shows "Status: No router found." A far as I can tell, this doesn't matter. I do have "Access your server over the Internet using an easy-to-remember address" checked in the same Network Settings page, and I used it to create the web address
http://epstewart.subsonic.org/. That worked OK: "Status: epstewart.subsonic.org responded successfully."
When I go to my second Mac and enter that URL in Safari, it automagically gets changed to
http://10.0.1.23:4040/index.view, where 10.0.1.23 is the IP address being used on my local network by my first Mac. That brings up the entire contents of my first Mac's iTunes Music folder -- the one I pointed Subsonic to in its Music Folders settings on the first Mac -- in the second Mac's browser window. I can then select any album, say, and play it from beginning to end ... indicating that Subsonic is working properly and the 4040 port address is being used properly on my first Mac (which, remember, is running the Subsonic app, which uses port address 4040, and is also running Lighthouse).
After confirming that all that was working, I installed the iSub app on my iPhone and tapped the gear icon at upper left of the iPhone screen when iSub was active to add a server:
http://epstewart.subsonic.org, with my Subsonic user name and password as I had configured them in Subsonic's Settings: Users browser pane. (Notice that I did not add ":4040" at the end of the
http://epstewart.subsonic.org Internet address.) Once I had entered the proper server information in iSub, I tapped that server item in iSub's server list and tapped "Make Default Server" in the Server Options dialog. I was told I had to quit and reopen iSub for this to take effect, so I did so. When I did, iSub opened with my entire iTunes Music collection from my first Mac and put it in view in iSub on the iPhone, and I was able to navigate to whatever song(s) I wanted to hear and play it/them!
So I learned two key things:
(1) Using Lighthouse on my main Mac means I didn't have to fool with AirPort Utility or change my AirPort Extreme's configuration in any way. (I assume this remains true if you have a router
other than an AirPort Extreme, by the say.)
(2) Using Lighthouse meant that it doesn't matter that "Automatically configure your router to allow incoming connections to Subsonic (UPnP port forwarding)" seemingly isn't working in the Subsonic Network Settings browser pane, but instead shows "Status: No router found." This seems to be a byproduct of (1) above. Since the router has not been made port 4040-aware, it doesn't port forward 4040 to the Mac at all ... but Lighthouse running the Mac fixes it up so port 4040
actually works for purposes of Subsonic streaming of music to other devices such as an iPhone running iSub.