an iOS and macOS project used to explore packet routing and NAT implementation in PacketTunnel.

how to run it

• open Xcode and compile/run the NAT-iOS target.

environment

• MacBook Pro (Retina, 15-inch, Mid 2015), macOS 10.12.6 (16G1114)
• MacBook Air (13-inch, Mid 2012), 10.12.6 (16G29)
• iPhone SE, iOS 9.3.3 (13G34)
• iPhone X, iOS 11.1.1 (15B150)

settings

• tun device ip is 10.25.1.1;
• set 115.239.210.27 to includedRoutes of tun device.
• tcp server 10.25.1.1:12345 running in containing app process;
• tcp server 10.25.1.1:12344 running in tunnel process;

what I am trying to implement or what I expect.

I am implementing an ip packet to socket byte array feature using NAT method. this feature is implemented in fqrouter on Androd. so I hope this feature can be implemented on iOS and macOS as well.

the following is the expected data flow in detail.

• browser visit a page, eg. 115.239.210.27, the request goes to tun device.
• PacketTunnel read request packet 10.25.1.1:54263 -> 115.239.210.27:80 from tun device, change it to 10.25.1.100:54263 -> 10.25.1.1:12344, and send the modified packet back to tun device.
• the tcp server listening at 10.25.1.1:12344 in tunnel process receive the modified packet, and create a new socket to receive the request data, and forward the request to the physical network device,
• tunnel process receive response data from physical network device, send it back to the socket in last step.
• response packet 10.25.1.1:12344 -> 10.25.1.100:54263 read from tun device, change it back to 115.239.210.27:80 -> 10.25.1.1:54263, send it back to tun device.
• browser process will receive the response data.

what actually happened or what the issues are.

1. tun didn't recieve the request packet according to the log. click ContainingAppTest button to test this behavior.
2. I make a tcp connect to 115.239.210.27:80 using createTCPConnectionThroughTunnelToEndpoint api, tun receive the packets and I NAT them to 10.25.1.1:12344 and send back to tun device, the tcp server listening at 10.25.1.1:12344 in PacketTunnel process didn't receive the new connection request. click ExtensionTest.ThroughTunnelToEndpoint button to test this behavior. the following is the log from iPhone X.

NAT2extension.log:5836:Mar 14 22:12:13 simpzans-iPhone PacketTunnel-iOS[700] <Notice>: -[TunnelServer testTcpConnectionThroughTunnel]
NAT2extension.log:5837:Mar 14 22:12:13 simpzans-iPhone PacketTunnel-iOS[700] <Notice>: error Error Domain=NSPOSIXErrorDomain Code=57 "Socket is not connected"
NAT2extension.log:5838:Mar 14 22:12:13 simpzans-iPhone PacketTunnel-iOS[700] <Notice>: in 10.25.1.1:52086 -> 115.239.210.27:80
NAT2extension.log:5839:Mar 14 22:12:13 simpzans-iPhone PacketTunnel-iOS[700] <Notice>: out 10.25.1.100:52086 -> 10.25.1.1:12344
NAT2extension.log:5840:Mar 14 22:12:14 simpzans-iPhone PacketTunnel-iOS[700] <Notice>: in 10.25.1.1:52086 -> 115.239.210.27:80
NAT2extension.log:5841:Mar 14 22:12:14 simpzans-iPhone PacketTunnel-iOS[700] <Notice>: out 10.25.1.100:52086 -> 10.25.1.1:12344
NAT2extension.log:5843:Mar 14 22:12:15 simpzans-iPhone PacketTunnel-iOS[700] <Notice>: in 10.25.1.1:52086 -> 115.239.210.27:80
NAT2extension.log:5844:Mar 14 22:12:15 simpzans-iPhone PacketTunnel-iOS[700] <Notice>: out 10.25.1.100:52086 -> 10.25.1.1:12344

but if I NAT the packets to 10.25.1.1:12345, and send it back to tun, the tcp server in containing app process did receive the packet. change proxyServerPort in NAT.m to appProxyPort and click ExtensionTest.ThroughTunnelToEndpoint to see this behavior. the following is the log from iPhone X.

NAT2app.log:2289:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: -[TunnelServer testTcpConnectionThroughTunnel]
NAT2app.log:2290:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: in 10.25.1.1:52135 -> 115.239.210.27:80
NAT2app.log:2291:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: out 10.25.1.100:52135 -> 10.25.1.1:12345
NAT2app.log:2292:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: error Error Domain=NSPOSIXErrorDomain Code=57 "Socket is not connected"
NAT2app.log:2293:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: in 10.25.1.1:12345 -> 10.25.1.100:52135
NAT2app.log:2294:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: out 115.239.210.27:80 -> 10.25.1.1:52135
NAT2app.log:2295:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: in 10.25.1.1:52135 -> 115.239.210.27:80
NAT2app.log:2296:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: out 10.25.1.100:52135 -> 10.25.1.1:12345
NAT2app.log:2297:Mar 14 22:13:26 simpzans-iPhone NAT-iOS[708] <Notice>: -[ProxyServer socket:didAcceptNewSocket:]
NAT2app.log:2298:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: in 10.25.1.1:12345 -> 10.25.1.100:52135
NAT2app.log:2299:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: out 115.239.210.27:80 -> 10.25.1.1:52135
NAT2app.log:2300:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: in 10.25.1.1:12345 -> 10.25.1.100:52135
NAT2app.log:2301:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: out 115.239.210.27:80 -> 10.25.1.1:52135
NAT2app.log:2302:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: in 10.25.1.1:12345 -> 10.25.1.100:52135
NAT2app.log:2303:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: out 115.239.210.27:80 -> 10.25.1.1:52135
NAT2app.log:2304:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: in 10.25.1.1:52135 -> 115.239.210.27:80
NAT2app.log:2305:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: out 10.25.1.100:52135 -> 10.25.1.1:12345
NAT2app.log:2306:Mar 14 22:13:26 simpzans-iPhone PacketTunnel-iOS[709] <Notice>: in 10.25.1.1:52135 -> 115.239.210.27:80

3. I run the same code in macOS, the 2 issues are reproduced and found another 1 issue. request packets from both createTCPConnectionToEndpoint and stringWithContentsOfURL apis in PacketTunnel process go to tun device. this behavior causes packets go through tun device infinitely. run NAT target to test these behaviors on macOS.

debug support files

• NAT2extension.iphonex.log file in DebugSupport dir is the log from iPhone X, NAT to tcp server in PacketTunnel process.
• NAT2app.iphonex.log, NAT to tcp server in app process.
• all source code at https://github.com/simpzan/nat