What is a VPN?

VPN, or Virtual Private Network, allows you to create a secure connection to another network over the Internet which can be very beneficial for some use cases. VPNs can be used for many things, for example – accessing region-restricted websites, shielding your browsing activity from bad guys on public Wi-Fi, connecting and using local resources which are inaccessible from the outside world, or simply creating a secure network between your servers and isolating them.
So, what are the common steps for creating a VPN? You need to first connect to the public internet through the ISP (Internet Service Provider), then initiate a VPN using client software. Sounds easy, right?
Well, it depends on the software you choose, whereby most of the VPN solutions follow the client-server principle. That means all nodes connect to e central server which is the central point to all others. In such an environment, the whole traffic passes through the central server creating a star topology, so this server needs lots of bandwidth. In case the central server fails and it’s not able to handle the whole traffic, the VPN will go down and the other members will not be able to communicate. This is the main disadvantage of such a setting. So, if you don’t want to have that single point of failure, you can use a full mesh topology, where every participant talks to the others without having a central server. If one of them fails, the other members will not be affected. A good, simple, and reliable peer-to-peer/full mesh solution is the PeerVPN.
09APRHere is a short guide for installing and configuring the PeerVPN software on RHEL:
1. Make sure that you can ping every server on its public IP.
2. Installing the necessary dependencies:

$ yum install gcc -y;
$ yum install openssl-devel -y;
$ yum install openssl -y;

3. Downloading the PeerVPN client:

$ curl -O http://peervpn.net/files/peervpn-0-044.tar.gz;

4. Unarchaving and compiling the software:

$ tar xzfv peervpn-0-044.tar.gz && cd peervpn-0-044 && make

5. Moving the binary:

$ cp peervpn /usr/sbin;

6. Create and edit the config file:

$ mkdir /etc/peervpn && nano /etc/peervpn/peervpn.conf

Sample content of the config file, with comments:
// This is the default UDP port that PeerVPN uses. You can change it, but make sure that you have an open in/outbound connection for this port (if you are server has iptables : iptables -S)port 7000
//This is the network name which can be anything you wantnetworkname MyPeerVPN
//This is a generated 512 shared key for encrypting the traffic between the peers. If you want to use encryption, make sure that the key is the same on each host. Use this command to create one:

$ openssl rand -base64 382 | tr -d 'n' && echo

//IMPORTANT: don use the same key from my example below
Psk VqmWsJje18/qqIOEN2+pLHugDtAcN5So03J0TL9wIQomAkQwcNR23SzM+m7cuJyCeyXXuHDLoKbzVbk
176eDVLPS8wLNoWSiwPF2yQn57Q4vjRz3qjI51nhE3yEyKmHZgotQga4Uz0vyvTGjJRxtPJqZ/igDN0YmI2
5nwhsYsyi34c6pIcqPCOHYlILndCUh8AYk3hGNPc0lSnkxW/sY+Uo+5BU0K6nB1LYcMlXA9Ij0deU+eyRTfoVg
gKnpXdl5FikrELbAOyoo71F0PEjL73k5fmyGmsoEE1f4yvgUXOKOzsPUaf567SP4Hm+h/EpqkWMR7JGc5
jBDsOlY52LTp5XaZNn+l+VEInCsFQiKgTW3zvzSmUcrPB3GqQ1KXknwfHmtCJe4SRiRZLKtSeTiPdPvXC0HBM
k+KK9TNk45dDUi3/ougCIwavMPEedH7Gh5fvG5iNXjZ24tAAOTle2oBHVgO2Wq7llh2VwKkrzyYATuchus
VLbHa98D0YR2wA==
enabletunneling yes
// This is the name of the network interface ( like eth0 )interface pvpn0
// this is the IP address range. Note that every peer should have a unique one in the same subnet, so simply increment the address for each new server. In my example I have the 10.1.1.1 , which will be the IP of the initialization peer.ifconfig4 10.1.1.1/24
//the initpeers is the initial host (its public IP/hostname + port) which has to be connected in order to discover the other hosts from the private network. This directive should be included only in the config files of the second, third… hostsinitpeers 165.165.165.165 7000
So here are two sample config files, the left is for the initialization peer and the right is for the other hosts:

In order to add one more host, simply copy the right configuration and set the next possible IP(ifconfig4) from the range
7. Create a system unit file in order to start the network on boot:

$ nano /usr/lib/systemd/system/peervpn.service

[Unit]Description=PeerVPN network serviceWants=network-online.targetAfter=network-online.target[Service]ExecStart=/usr/sbin/peervpn /etc/peervpn/peervpn.conf[Install]WantedBy=multi-user.target
8. Start and enable the PeerVPN:

$ systemctl start peervpn.service
$ systemctl enable peervpn.service

9. Check the service for listening:

$ netstat -tupanl | grep peervpn

The output should look like this (if IPv6 is enabled):
udp 0 0 0.0.0.0:7000 0.0.0.0:* 5766/peervpnudp6 0 0 :::7000 :::* 5766/peervpn
10. Ping each host using the VPN IP address