### Send/Recv Udp Packet as Raw Packet with TCP header,ICMP header
Which can help you bypass udp blocking or udp QOS or just poorly supported udp NAT behavior by some ISP. Raw packet with UDP header is also supported,in this way you can just make use of the encrpyting and anti-replay feature.
Encrypt your traffic with aes128cbc,protects data integrity by md5 or crc32,protect replay attack with an anti-replay window smiliar to ipsec/openvpn.Client and server use pre shared secret to verify each other,man-in-the-middle is impossible.
Simulated 3-way handshake,simluated seq ack_seq. Simluated tcp options:MSS,sackOk,TS,TS_ack,wscale. Provides real-time delivery ,no tcp over tcp problem when using openvpn.
Conection failure detection by hearbeat. After hearbeat timeouts,client will auto change port and re-connect.if re-connection is successful,the previous connection will be recovered,and all existed udp conversations will stay vaild.
For example,if you use udp2raw+openvpn.Openvpn wont lose connection after reconnect,**Even if you re-insert your net cable,or connect to a new wifi,existing openvpn connection will stay vaild**.
linux host(include desktop linux,openwrt router,raspberry pi),root access. if you want to use it on window,you can use VMware(both bridged mode and nat mode are supported).
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.
```
run at client side:
./udp2raw_amd64 -c -l0.0.0.0:3333 -r44.55.66.77:4096 -a -k "passwd" --raw-mode faketcp
run at server side:
./udp2raw_amd64 -s -l0.0.0.0:4096 -r 127.0.0.1:7777 -a -k "passwd" --raw-mode faketcp
```
Now,your client and server established a tunnel thorough tcp port 4096. Connecting to udp port 3333 at client side is equivalent with connecting to port 7777 at server side. No udp traffic will be exposed to outside.
this programs sends packet via raw socket.In faketcp mode,Linux Kernel TCP packet processing has to be blocked by a iptables rule on both sides,otherwise Kernel will automatically send RST for unrecongized TCP packet and you will sustain from stability/peformance problem.You can use -a option to let the program automatically add/del iptables rule on start/exit.You can also use the -g option to generate iptables rule and add it manually.
Its suggested to use aes128cbc + md5 to obtain maxmized security.If you want to run the program on a router,you can try xor+simple,it can fool Packet Inspection by firewalls most time, but it cant protect you from serious attackers. Mode none is only for debug,its not suggest to set cipher-mode or auth-mode to none.
### seq-mode
the faketcp mode doest not behave 100% like a real tcp connection.ISP may be able to distinguish the simulated tcp traffic from real tcp traffic(though its costly). seq-mode can help you changed the seq increase behavior a bit. If you experienced problems,try to change the value.
(iperf3 udp mode is not used bc of bug mentioned in this issue: https://github.com/esnet/iperf/issues/296 ,instead,we turn iperf3 's tcp traffic into udp by using openvpn,to test udp2raw 's peformance. Read [Application](https://github.com/wangyu-/udp2raw-tunnel#application) for detail )
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.
