@node User manual
@unnumbered User manual

GoVPN is split into two pieces: client and server. Each of them work on
top of UDP and TAP virtual network interfaces. Client and server have
several common configuration command line options:

@table @asis
@item Timeout
Because of stateless UDP nature there is no way to know if
remote peer is dead, but after some timeout. Client and server
heartbeats each other every third part of heartbeat. Also this timeout
is the time when server purge his obsolete handshake and peers states.
@item Allowable nonce difference
To prevent replay attacks we just remembers
latest received nonce number from the remote peer and drops those who
has lower ones. Because UDP packets can be reordered during: that
behaviour can lead to dropping of not replayed ones. This options gives
ability to create some window of allows difference. That opens the door
for replay attacks for narrow time interval.
@item MTU
Maximum transmission unit.
@end table

Client needs to know his identification, path to the authentication key,
remote server's address, TAP interface name, and optional path to up and
down scripts, that will be executed after connection is either initiated
or terminated.

Server needs to know only the address to listen on and path to directory
containing peers information. This directory must contain subdirectories
with the names equal to client's identifications. Each of them must have
key file with corresponding authentication key, up.sh script that has to
print interface's name on the first line and optional down.sh.

@menu
* Example usage::
@end menu

@node Example usage
@section Example usage

Let's assume that there is some insecure link between your computer and
WiFi-reachable gateway. You have got preconfigured @code{wlan0} network
interface with 192.168.0/24 network. You want to create virtual
encrypted and authenticated 172.16.0/24 network and use it as a default
transport. MTU for that wlan0 is 1500 bytes. GoVPN will say that maximum
MTU for the link is 1476, however it does not take in account TAP's
Ethernet frame header length, that in my case is 14 bytes long (1476 - 14).

Do not forget about setting @code{GOMAXPROC} environment variable for
using more than one CPU.

At first you have to generate client's authentication key and client's
unique identification. There is @code{utils/newclient.sh} script for
convenience.

@example
% ./utils/newclient.sh Alice
peers/9b40701bdaf522f2b291cb039490312/Alice
@end example

@code{9b40701bdaf522f2b291cb039490312} is client's identification.
@code{Alice} is just an empty file that can help to search them like
this: @verb{|find peers -name Alice|}. @code{key} file inside peer's
directory contains authentication key.

GNU/Linux IPv4 client-server example:

@example
server% echo "#!/bin/sh" > peers/CLIENTID/up.sh
server% echo "echo tap10" >> peers/CLIENTID/up.sh
server% chmod 500 peers/CLIENTID/up.sh
server% ip addr add 192.168.0.1/24 dev wlan0
server% tunctl -t tap10
server% ip link set mtu 1462 dev tap10
server% ip addr add 172.16.0.1/24 dev tap10
server% ip link set up dev tap10
server% GOMAXPROC=4 govpn-server -bind 192.168.0.1:1194
@end example

@example
client% umask 066
client% echo MYLONG64HEXKEY > key.txt
client% ip addr add 192.168.0.2/24 dev wlan0
client% tunctl -t tap10
client% ip link set mtu 1462 dev tap10
client% ip addr add 172.16.0.2/24 dev tap10
client% ip link set up dev tap10
client% ip route add default via 172.16.0.1
client% export GOMAXPROC=4
client% while :; do
    govpn-client -key key.txt -id CLIENTID -iface tap10 -remote 192.168.0.1:1194
done
@end example

FreeBSD IPv6 client-server example:

@example
server% cat > peers/CLIENTID/up.sh <<EOF
#!/bin/sh
$tap=$(ifconfig tap create)
ifconfig $tap inet6 fc00::1/96 mtu 1462 up
echo $tap
EOF
server% chmod 500 peers/CLIENTID/up.sh
server% ifconfig em0 inet6 fe80::1/64
server% GOMAXPROC=4 govpn-server -bind fe80::1%em0
@end example

@example
client% ifconfig me0 inet6 -ifdisabled auto_linklocal
client% ifconfig tap10
client% ifconfig tap10 inet6 fc00::2/96 mtu 1462 up
client% route -6 add default fc00::1
client% export GOMAXPROC=4
client% while :; do
    govpn-client -key key.txt -id CLIENTID -iface tap10 -remote [fe80::1%me0]:1194
done
@end example

Example up-script:

@example
client% cat > up.sh <<EOF
#!/bin/sh
dhclient $1
rtsol $1
EOF
client% chmod +x up.sh
client% govpn -id CLIENTID -key key.txt -iface tap10 -remote [fe80::1%me0]:1194 -up ./up.sh
@end example

Client will exit if won't finish handshake during @code{-timeout}.
If no packets are received from remote side during timeout, then daemon
will stop sending packets to the client and client will exit. In all
cases you have to rehandshake again.