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:

[17:23:05] [Client thread/INFO]: Connecting to 168.192.2.16, 25565
[17:23:35] [Server Connector #8/ERROR]: Couldn't connect to server
io.netty.channel.ConnectTimeoutException: connection timed out: /168.192.2.16:25565
    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.
• Why do I get 'UnknownHostException: session.minecraft.net' when attempting to log in to Minecraft 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?