I can't connect to a friend's Minecraft server, but none of the usual culprits seem to be the problem

I'm trying to connect to a friend's Minecraft server, but I'm not able to do so. We've double-checked the usual culprits brought up in most Minecraft server tutorials, but we're still not having any luck.

This is our specific situation:

I'm on a Mac OSX machine and want to connect to my friend's server. He's running the server and a client at the same time on his Windows machine. We're both on the same local network. He's able to start and connect to his server. Whenever I try to connect to his server using our external IP address, however, I get the following error:

This is what my log looks like when I try to connect to his server from our external IP address:

[16:45:46] [Client thread/INFO]: Connecting to [IP address], 25565
[16:45:46] [Server Connector #1/ERROR]: Couldn't connect to server
java.net.ConnectException: Connection refused: /[IP address]:25565
    at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method) ~[?:1.6.0_65]
    at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:599) ~[?:1.6.0_65]
    at io.netty.channel.socket.nio.NioSocketChannel.doFinishConnect(NioSocketChannel.java:208) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at io.netty.channel.nio.AbstractNioChannel$AbstractNioUnsafe.finishConnect(AbstractNioChannel.java:287) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:528) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:468) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:382) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:354) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at java.lang.Thread.run(Thread.java:695) ~[?:1.6.0_65]

When I try to connect to his server by using his internal IP address for the server, I get this error:

And this is in my log file:

[13:52:08] [Client thread/INFO]: Connecting to 192.168.2.16, 25565
[13:52:38] [Server Connector #1/ERROR]: Couldn't connect to server
io.netty.channel.ConnectTimeoutException: connection timed out: /192.168.2.16:25565
    at io.netty.channel.nio.AbstractNioChannel$AbstractNioUnsafe$1.run(AbstractNioChannel.java:213) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at io.netty.util.concurrent.PromiseTask$RunnableAdapter.call(PromiseTask.java:38) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at io.netty.util.concurrent.ScheduledFutureTask.run(ScheduledFutureTask.java:123) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:380) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:357) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:116) ~[netty-all-4.0.23.Final.jar:4.0.23.Final]
    at java.lang.Thread.run(Thread.java:695) ~[?:1.6.0_65]

In both cases, when we check my friend's server logs, it looks like the server is running properly, and it never receives a request from my client to join the server.

These are some things we've already tried:

• We've double- and triple-checked our router's port forwarding settings. They are certainly correct.
• As you can see above, I've tried to connect to the server using both its internal and external IP addresses.
• We've made sure that his Windows Firewall settings and my Mac OSX firewall settings aren't blocking Minecraft on either of our computers.

None of these have helped.

I've also looked at these similar questions on Arquade, none of which have helped:

• Can't connect to Minecraft server says to make sure I can connect to minecraft.net. I can.
• Can't connect to servers? discusses a different Java networking exception than the ones I'm getting when I try to connect.
• Why can't I connect to my minecraft server? discusses not being able to connect to a server that you're hosting. My friend can connect to his server from the computer he's hosting it on, so that's not our problem.
• I am having problems connecting to the Minecraft server from a 2nd machine in the local network discusses poor performance once one has connected to a Minecraft server with a Windows machine, but I can't even connect.

What are some other things my friend and I should check to better diagnose and fix our issues connecting to his server?

Here are some more things to try before giving up:

1. Check that in your friend's server.properties the server-ip is set to your friend's internal ip NOT localhost or 127.0.0.1
2. Try with a LAN server, have your friend open a world to LAN (with cheats), and type the command /publish, this will give you the port you need to connect to so connect to 192.168.2.16:[whatever port Minecraft gives you]
3. disable any and all firewalls, and then try connecting on a dedicated and a LAN server as in suggestion 2
4. Try hosting the server on your end, it may be a mac protection problem or a java problem on his computer. Remember suggestion 1 as you reconfigure your new server. Also try a LAN server from your end.
5. Try a new port/check that nothing is using 25565. Although I doubt this would be the problem its is worth a try.
6. Make sure your router firewall allows your local traffic through, I can't tell you how to do this for your router but give the firewall or DMZ tabs a check to make sure nothing funky is going on.
7. Although I doubt this will work, you can try setting online-mode to false

Best of luck, I hope this helps. I had something like this happen to me one time but with 2 macs and 2 windows, after two weeks it seemed to clear itself up.

When you are on the same network there is no need for port forwarding but you do need the port in the server properties (default 25565) matched with what you use to connect (for the default port 25565 you don't need to type it after the ip).

If you look for your ip I suggest you to go open cmd and type ipconfig. Now you have all your internal ip's, but you have to use the right one: ethernet or wireless ipv4. You might be using some virtual network ip like hamachi which will not work.

If you are on the same network I suggest to always use the internal ip because it might be faster.