#!/usr/bin/env bash
#
#  - create GRE tunnel between two servers
#  - pass all traffic from specified network to GRE tunel
#

####### LINUX #######

PATH="/bin:/usr/sbin:/usr/bin:/sbin:/usr/local/bin:/usr/local/sbin"
TUNNEL_IF=gre10
VPN_NETWORK=10.254.0.0/16

# entry node
LOCAL_ADDR_EXT=162.210.201.13
LOCAL_ADDR_INT=10.254.10.1

# exit node
REMOTE_ADDR_EXT=88.32.99.91
REMOTE_ADDR_INT=10.254.20.1

#####################

# create gre interface
ip tunnel add "$TUNNEL_IF" mode gre local "$LOCAL_ADDR_EXT" remote "$REMOTE_ADDR_EXT" ttl 255

# start interface
ip link set "$TUNNEL_IF" up

# setup internal address on interface
ip addr add "$LOCAL_ADDR_INT" dev "$TUNNEL_IF"

# add route to exit node
route add -net "${REMOTE_ADDR_INT%.*}.0" netmask 255.255.255.0 gw "$LOCAL_ADDR_INT"

# create rule for vpn network
ip rule add from $VPN_NETWORK table 10

# add default rule for vpn table
ip route add default via "$LOCAL_ADDR_INT" table 10