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Using Windows Firewall, when I receive a connection, the originating IP is displayed as the IP address of my router/gateway instead of the actual originating IP address of the connection. My router is an ASUS RT-N16 with dd-wrt build 14896, and the server I am experiencing this issue on is running Windows Server 2008 R2 SP1.

2012-08-05 23:01:03 ALLOW TCP 60597 25565 0 - 0 0 0 - - - RECEIVE
2012-08-05 23:01:04 ALLOW TCP 60601 3389 0 - 0 0 0 - - - RECEIVE
2012-08-05 23:01:12 ALLOW UDP 55238 53 0 - - - - - - - SEND is the IP address of my server, and is the IP address of my router. I have tried with DMZ on/off and with Windows Firewall on/off, to the same results.

Additionally, my Minecraft server also displays only my router's IP address, instead of the actual player's IP address (names in log were changed to "player"):

[INFO] player[/] logged in with entity id 10445 at (-782.984331133011, 99.63587500882896, 294.12718027903713)
[INFO] player[/] logged in with entity id 145517 at (-166.5, 64.62000000476837, 257.5)
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up vote 3 down vote accepted

Your public IP is assigned to your router. And it's the only IP you have that's reachable from outside your LAN. If people connect to your router's IP address, the packet will go to your router.

The router can't forward that packet to your server with the router's IP address as its destination. If it did, your server would just forward it back to the router rather than processing it locally.

Similarly, in order for the return packet to go to the right destination, the router must ensure the replies go to the router. So the source address (as seen by the server) will always be in the direction of the router (never another LAN IP).

So this is all expected behavior with port forwarding and hairpin NAT. Connections from outside your LAN should show the correct source IP address at the server. Otherwise, it's all rewritten by the router to make sure all the packets go through the router.

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Ah, thank you. I swear I remember my Minecraft server showing the actual IP addresses of players in the log though. With DMZ, however, shouldn't the server be outside of the router's firewall and therefore outside of NAT? Or does it still stay behind NAT? I need to read up on this. – Huskehn Aug 6 '12 at 4:30
@Huskehn: Are you talking about connections from your own LAN or connections from the Internet? If the connections are from the Internet, you should see the correct source IP address. If connections are from your own LAN, you will see the correct source IP address if, and only if, the connections are to the server's LAN IP address. If you connect using loopback NAT (from your LAN but to the Internet IP address), the source address must be changed otherwise the router cannot ANT the reply packets and the connections will fail. – David Schwartz Aug 6 '12 at 7:58

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