This repo is just an answer on a question "how much time it'll take to write my own simple VPN in golang"
It was less than I can ever image - little bit more than 3 hours.
Update: next 30 minut was spent on dynamic config reloading on HUP signal
Update: next 2 hours to use only one UDP socket, support broadcast and multicast, support config reload and encryption key change without going offline
Update: and about 30 minutes more to implement multithread + so_socket

So, LCVPN is

• Very light and easy (one similar config on all hosts)
• Use same config for all hosts (autedetect local params) - useful with puppet etc
• Uses AES-128, AES-192 or AES-256 encryption (note that AES-256 is much slower than AES-128 on most conputers)
• Communicates via UDP directly to selected host (no central server)
• Works only on Linux (uses TUN device)
• Support of basic routing - can be used to connect several networks
• Multithread send and receive - scaleable for big traffc
• Due to use so_reuseport better result in case of bigger number of hosts
• It's still in beta stage, use it on your risk

You need golang (at least 1.5) installed and configured:

$ go install github.com/kanocz/lcvpn

if you have config in /etc/lcvpn.conf

$ sudo $GOPATH/bin/lcvpn

if you want to specify different location of config (or if you need to run several instances)

$ sudo $GOPATH/bin/lcvpn -config lcvpn.conf

if you host is hidden behind firewall (with udp port forward) lcvpn is unable to detect which "remote" is localhost. In this case use next syntax:

$ sudo $GOPATH/bin/lcvpn -local berlin -config lcvpn.conf

[main]
port = 23456
aeskey = 4A34E352D7C32FC42F1CEB0CAA54D40E9D1EEDAF14EBCBCECA429E1B2EF72D21
#altkey = 1111111117C32FC42F1CEB0CAA54D40E9D1EEDAF14EBCBCECA429E1B2EF72D21
broadcast = 192.168.3.255
netcidr = 24
recvThreads = 4
sendThreads = 4

[remote "prague"]
ExtIP = 46.234.105.229
LocIP = 192.168.3.15
route = 192.168.10.0/24
route = 192.168.15.0/24
route = 192.168.20.0/24

[remote "berlin"]
ExtIP = 103.224.182.245
LocIP = 192.168.3.8
route = 192.168.11.0/24

[remote "kiev"]
ExtIP = 95.168.211.37
LocIP = 192.168.3.3

where port is UDP port for communication
aeskey is hex form of 16, 24 or 32 bytes key (for AES-128, AES-192 or AES-256)
number of remotes is virtualy unlimited, each takes about 256 bytes in memory

Config is reloaded on HUP signal. In case of invalid config just log message will appeared, previous one is used.
P.S.: listening udp socket is not reopened for now, so on port change restart is needed

altkey configuration option allows specify alternative AES key that will be used in case if decription with primary one failed. This allow to use next algoritm to change keys without link going offline:

• In normal state only aeskey is set (setting altkey is more cpu-consuming)
• Set altkey to new key on all hosts and send HUP signal
• Exchange altkey and aeskey on all hosts and send HUP signal
• Remove altkey (with old key) from configs on all hosts and send HUP signal again
• We are running with new key :)

Don't know what more to implement... please let me know if you need something