[![Release][1]][2] [![Powered][7]][8] [![Build Status][3]][4] [![Go Report Card][5]][6] [1]: https://img.shields.io/github/release/xtaci/kcptun.svg [2]: https://github.com/xtaci/kcptun/releases/latest [3]: https://travis-ci.org/xtaci/kcptun.svg?branch=master [4]: https://travis-ci.org/xtaci/kcptun [5]: https://goreportcard.com/badge/github.com/xtaci/kcptun [6]: https://goreportcard.com/report/github.com/xtaci/kcptun [7]: https://img.shields.io/badge/KCP-Powered-blue.svg [8]: https://github.com/skywind3000/kcp

A tool for converting TCP stream into KCP stream, Download Now!

kcptun is based on kcp-go

QuickStart

Client, server, respectively, download the corresponding platform binary compression package, and extract, through the following command to start port forwarding.

Server: ./server_linux_amd64 -t "SERVER_IP:8388" -l ":4000" -mode fast2
Client: ./client_darwin_amd64 -r "SERVER_IP:4000" -l ":8388" -mode fast2

The above command can establish 8388/tcp port forwarding (through 4000/udp port).

Performance

* Speed tested with: https://fast.com * WAN Link Speed: 100M ADSL * WIFI: 5GHz TL-WDR3320

Usage

Help output under MacOS X:

$ ./client_darwin_amd64 -h
NAME:
   kcptun - client(with SMUX)

USAGE:
   client_darwin_amd64 [global options] command [command options] [arguments...]

VERSION:
   20170120

COMMANDS:
     help, h  Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --localaddr value, -l value      local listen address (default: ":12948")
   --remoteaddr value, -r value     kcp server address (default: "vps:29900")
   --key value                      pre-shared secret between client and server (default: "it's a secrect") [$KCPTUN_KEY]
   --crypt value                    aes, aes-128, aes-192, salsa20, blowfish, twofish, cast5, 3des, tea, xtea, xor, none (default: "aes")
   --mode value                     profiles: fast3, fast2, fast, normal (default: "fast")
   --conn value                     set num of UDP connections to server (default: 1)
   --autoexpire value               set auto expiration time(in seconds) for a single UDP connection, 0 to disable (default: 0)
   --mtu value                      set maximum transmission unit for UDP packets (default: 1350)
   --sndwnd value                   set send window size(num of packets) (default: 128)
   --rcvwnd value                   set receive window size(num of packets) (default: 512)
   --datashard value, --ds value    set reed-solomon erasure coding - datashard (default: 10)
   --parityshard value, --ps value  set reed-solomon erasure coding - parityshard (default: 3)
   --dscp value                     set DSCP(6bit) (default: 0)
   --nocomp                         disable compression
   --snmplog value                  collect snmp to file, aware of timeformat in golang, like: ./snmp-20060102.log
   --snmpperiod value               snmp collect period, in seconds (default: 60)
   --log value                      specify a log file to output, default goes to stderr
   -c value                         config from json file, which will override the command from shell
   --help, -h                       show help
   --version, -v                    print the version

$ ./server_darwin_amd64 -h
NAME:
   kcptun - server(with SMUX)

USAGE:
   server_darwin_amd64 [global options] command [command options] [arguments...]

VERSION:
   20170120

COMMANDS:
     help, h  Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --listen value, -l value         kcp server listen address (default: ":29900")
   --target value, -t value         target server address (default: "127.0.0.1:12948")
   --key value                      pre-shared secret between client and server (default: "it's a secrect") [$KCPTUN_KEY]
   --crypt value                    aes, aes-128, aes-192, salsa20, blowfish, twofish, cast5, 3des, tea, xtea, xor, none (default: "aes")
   --mode value                     profiles: fast3, fast2, fast, normal (default: "fast")
   --mtu value                      set maximum transmission unit for UDP packets (default: 1350)
   --sndwnd value                   set send window size(num of packets) (default: 1024)
   --rcvwnd value                   set receive window size(num of packets) (default: 1024)
   --datashard value, --ds value    set reed-solomon erasure coding - datashard (default: 10)
   --parityshard value, --ps value  set reed-solomon erasure coding - parityshard (default: 3)
   --dscp value                     set DSCP(6bit) (default: 0)
   --nocomp                         disable compression
   --snmplog value                  collect snmp to file, aware of timeformat in golang, like: ./snmp-20060102.log
   --snmpperiod value               snmp collect period, in seconds (default: 60)
   --log value                      specify a log file to output, default goes to stderr
   -c value                         config from json file, which will override the command from shell
   --help, -h                       show help
   --version, -v                    print the version

Parameters by Layers

Both sides must agree on the following parameters:

• datashard
• parityshard
• nocomp
• key
• crypt

other parameters can be set independently.

How to optimize：

Step 1：Increase client -rcvwnd & server -sndwnd simultaneously & gradually。
Step 2：Try download something and observer, if the bandwidth usage is close the limit then stop, otherwise goto step 1.

NOTICE: if too much retranmission happens, it's quite possible the windows are too large

Embeded Mode

Aggresiveness On Retransmission:

fast3 > fast2 > fast > normal > default

Manual control is supported with hidden parameters, you must understand KCP protocol before doing this.

 -mode manual -nodelay 1 -resend 2 -nc 1 -interval 20

Forward Error Correction

In coding theory, the Reed–Solomon code belongs to the class of non-binary cyclic error-correcting codes. The Reed–Solomon code is based on univariate polynomials over finite fields.

It is able to detect and correct multiple symbol errors. By adding t check symbols to the data, a Reed–Solomon code can detect any combination of up to t erroneous symbols, or correct up to ⌊t/2⌋ symbols. As an erasure code, it can correct up to t known erasures, or it can detect and correct combinations of errors and erasures. Furthermore, Reed–Solomon codes are suitable as multiple-burst bit-error correcting codes, since a sequence of b + 1 consecutive bit errors can affect at most two symbols of size b. The choice of t is up to the designer of the code, and may be selected within wide limits.

Setting parameters of RS-Code with -datashard m -parityshard n

DSCP

Differentiated services or DiffServ is a computer networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying and managing network traffic and providing quality of service (QoS) on modern IP networks. DiffServ can, for example, be used to provide low-latency to critical network traffic such as voice or streaming media while providing simple best-effort service to non-critical services such as web traffic or file transfers.

DiffServ uses a 6-bit differentiated services code point (DSCP) in the 8-bit differentiated services field (DS field) in the IP header for packet classification purposes. The DS field and ECN field replace the outdated IPv4 TOS field.[1]

setting each side with -dscp value.

Security

No matter what encryption you are using for application layer, if you specify -crypt none to kcptun, the header will be PLAINTEXT to everyone; I suggest -crypt aes-128 for encryption at least .

NOTICE: -crypt xor is also insecure, do not use this unless you know what you are doing.

Memory Control

Routers, mobile devices are sensitive to memory consumption; by setting GOGC environment(eg: GOGC=20) will lower memory consumption. Reference: https://blog.golang.org/go15gc

Traffic Control

Intended audience : for those server's bandwidth is quite limited.

Example: To limit outgoing bandwidth to 32mbit/s on server.

root@kcptun:~# cat tc.sh
tc qdisc del dev eth0 root
tc qdisc add dev eth0 root handle 1: htb
tc class add dev eth0 parent 1: classid 1:1 htb rate 32mbit
tc filter add dev eth0 protocol ip parent 1:0 prio 1 handle 10 fw flowid 1:1
iptables -t mangle -A POSTROUTING -o eth0  -j MARK --set-mark 10
root@kcptun:~#

Snappy Stream Compression

Snappy is a compression/decompression library. It does not aim for maximum compression, or compatibility with any other compression library; instead, it aims for very high speeds and reasonable compression. For instance, compared to the fastest mode of zlib, Snappy is an order of magnitude faster for most inputs, but the resulting compressed files are anywhere from 20% to 100% bigger.

Reference: http://google.github.io/snappy/

disable compression by setting -nocomp on both side.

Tips: Turning off compression may reduce latency.

SNMP

// Snmp defines network statistics indicator
type Snmp struct {
	BytesSent        uint64 // payload bytes sent
	BytesReceived    uint64
	MaxConn          uint64
	ActiveOpens      uint64
	PassiveOpens     uint64
	CurrEstab        uint64
	InErrs           uint64
	InCsumErrors     uint64 // checksum errors
	InSegs           uint64
	OutSegs          uint64
	OutBytes         uint64 // udp bytes sent
	RetransSegs      uint64
	FastRetransSegs  uint64
	EarlyRetransSegs uint64
	LostSegs         uint64
	RepeatSegs       uint64
	FECRecovered     uint64
	FECErrs          uint64
	FECSegs          uint64 // fec segments received
}

Sending a signal by kill -SIGUSR1 pid will give SNMP information for KCP，useful for fine-grained adjustment. Of which RetransSegs,FastRetransSegs,LostSegs,OutSegs is the most useful.

References

1. https://github.com/skywind3000/kcp -- KCP - A Fast and Reliable ARQ Protocol.
2. https://github.com/klauspost/reedsolomon -- Reed-Solomon Erasure Coding in Go.
3. https://en.wikipedia.org/wiki/Differentiated_services -- DSCP.
4. http://google.github.io/snappy/ -- A fast compressor/decompressor.
5. https://www.backblaze.com/blog/reed-solomon/ -- Reed-Solomon Explained.
6. http://www.qualcomm.cn/products/raptorq -- RaptorQ Forward Error Correction Scheme for Object Delivery.
7. https://en.wikipedia.org/wiki/PBKDF2 -- Key stretching.
8. http://blog.appcanary.com/2016/encrypt-or-compress.html -- Should you encrypt or compress first?
9. https://github.com/hashicorp/yamux -- Connection multiplexing library.
10. https://tools.ietf.org/html/rfc6937 -- Proportional Rate Reduction for TCP.
11. https://tools.ietf.org/html/rfc5827 -- Early Retransmit for TCP and Stream Control Transmission Protocol (SCTP).
12. http://http2.github.io/ -- What is HTTP/2?
13. http://www.lartc.org/ -- Linux Advanced Routing & Traffic Control