Summary

This script is used to tunnel to a remote network, not just a remote machine.
Development and testing was done on Ubuntu 16.04 desktop with an Ubuntu 16.04 server. 

There must be a cert provided for connection however, it can be embeded directly into
the script (see the below information for more details). When executed, this script will
generate a server configuration script, send it to the remote server, executes the 
configuration on the remote server, creates the local routes and adapters, then establish 
the tunnel. Once the tunnel is broken using ctrl+c the script will reverse server 
configurations, delete the server configuration file, and delete the tun adapters. 

Other than a private certificate to access the server, there should be 
no addtional setup to make this virtual private network tunnel work*.

Syntax

sshvpn.sh (presented with defaults)
                             (-s | --server "DEFAULT")?
                             (-p | --port "DEFAULT")?
                             (-u | --username "DEFAULT")?
                             (-i | --identity_file "DEFAULT")?
                             (-l | --local_address "DEFAULT")?
                             (-r | --remote_address "DEFAULT")?
                             (-c | --cidr_blocks "DEFAULT")?

-s | --server         : The ip address or DNS address of the remote server.
-p | --port           : The port listening for ssh connections on the remote server.
-u | --username       : The username used for logging in and for sudo access on the remote server.
-i | --identity_file  : The private key used to connect to the remote server.
-l | --local_address  : The ip address assigned to the local tun adapter.
-r | --remote_address : The ip address assigned to the remote tun adapter.
-c | --cidr_blocks    : The comma seperated list of cidr blocks to route through the tun adapter.

Additional Details

If default vaules are desired, they can be set on lines 40 - 65 of the script. 
The default defaults are displayed below. Additionally, a private certificate 
can be embeded into the script on lines 80-90.

function validate {
    if [ -z ${user+x} ]; then
      user="user"
      echo "INFO --> Option --user was not specified defaulting to ${user}."
    fi
    if [ -z ${serv+x} ]; then
      serv="example.com"
      echo "INFO --> Option --serv was not specified defaulting to ${serv}."
    fi
    if [ -z ${port+x} ]; then
      port="22"
      echo "INFO --> Option --port was not specified defaulting to ${port}."
    fi
    if [ -z ${cert+x} ]; then
      cert=".tunKey"
      echo "INFO --> Option --cert was not specified defaulting to ${cert}."
    fi
    if [ -z ${addr+x} ]; then
      addr="1.1.1.2"
      echo "INFO --> Option --addr was not specified defaulting to ${addr}."
    fi
    if [ -z ${peer+x} ]; then
      peer="1.1.1.1"
      echo "INFO --> Option --peer was not specified defaulting to ${peer}."
    fi
    if [ -z ${frwd+x} ]; then
      frwd="192.168.0.0/24,192.168.1.0/24"
      echo "INFO --> Option --frwd was not specified defaulting to ${frwd}."
    fi
}

function tunKeyWrite {
if [ ! -f ${cert} ]; then
echo "-----BEGIN RSA PRIVATE KEY-----
INSERT PRIVATE KEY HERE
-----END RSA PRIVATE KEY-----" | tee ${cert} > /dev/null 2>&1
tunKeyWritten=yes
fi
}

The ssh command establishing the tunnel is below for convieniance. This is executed
after the adapters and routes have been setup on both the server and the client.
ssh -C -n -w 0:0 -i ${cert} -p ${port} ${user}@${serv}

*(depending on linux distro)