An encrpyted, anti-replay, multiplexing UDP tunnel which tunnels UDP traffic with fake TCP or ICMP header using raw socket. Also acts as a connection stablizer.
Fake headers help you bypass UDP blocking, UDP QOS or improper UDP NAT behavior on some ISPs. Raw packets with UDP headers are also supported, where you can just use the encrpyting and anti-replay feature.
Simulates the 3-way handshake, along with seq and ack_seq. TCP options MSS, sackOk, TS, TS_ack, wscale are also simulated. Real-time delivery guaranteed, no TCP over TCP problem when using OpenVPN.
Conection failures are detected by heartbeats. If timed-out, the client will automatically change the port number and reconnect. If reconnection is successful, the previous connection will be recovered, and all existing UDP conversations will stay vaild.
For example, if you use UDP2RAW + OpenVPN, OpenVPN won't lose connection after any reconnect, **even if the network cable is re-plugged or the WiFi access point is changed**.
Assume your UDP is blocked or being QOS-ed or just poorly supported. Assume your server ip is 44.55.66.77, you have a service listening on udp port 7777.
Now, the client and the server have established a tunnel through TCP port 4096. Connecting to UDP port 3333 at the client side is equivalent to connecting to port 7777 at the server side. No UDP traffic will be exposed.
This program sends packets via raw socket. In FakeTCP mode, Linux kernel TCP packet processing has to be blocked by a iptables rule on both sides, otherwise the kernel will automatically send RST for an unrecongized TCP packet and you will sustain from stability / peformance problems. You can use `-a` option to let the program automatically add / delete iptables rule on start / exit. You can also use the -g option to generate iptables rule and add it manually.
### `cipher-mode` and `auth-mode`
It is suggested to use AES-128-CBC + MD5 to obtain maximum security. If you want to run the program on a router, you can try XOR + simple, which can fool packet inspection by firewalls the most of time, but it cannot protect you from serious attacks. Mode none is only for debugging purpose. It is not recommended to set the cipher-mode or auth-mode to none.
The FakeTCP mode does not behave 100% like a real tcp connection. ISPs may be able to distinguish the simulated tcp traffic from the real TCP traffic (though it's costly). seq-mode can help you change the seq increase behavior slightly. If you experience any problems, try to change the value.
(iperf3 UDP mode is not used because of a bug mentioned in this issue: https://github.com/esnet/iperf/issues/296 . Instead, we package the TCP traffic into UDP by OpenVPN to test the performance. Read [Application](https://github.com/wangyu-/udp2raw-tunnel#application) for details.
kcptun is a tcp connection speed-up program,it speeds-up tcp connection by using kcp protocol on-top of udp.by using udp2raw,you can use kcptun while udp is QoSed or blocked.
### speed-up tcp connection via raw traffic by using udp2raw+finalspeed
finalspeed is a tcp connection speed-up program similiar to kcptun,it speeds-up tcp connection by using kcp protocol on-top of udp or tcp.but its tcp mode doesnt support openvz,you can bypass this problem if you use udp2raw+finalspeed together,and icmp mode also becomes avaliable.
