Working with OpenVPN (and iptables)

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Working with OpenVPN (and iptables)

Understanding Virtual Private Networks (VPsN) is essential for many advanced level certification tests. OpenVPN is a popular VPN solution that enjoys somewhat common use. This exercise focuses on configuring a basic VPN server and client.

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Lab Info

Level

Advanced

Last updated

Apr 06, 2025

Duration

1h 30m

Challenge

Install and configure the OpenVPN server on `vpn-server`.
Install OpenVPN:
1. Run yum install -y openvpn.
2. Copy the server config: cp /usr/share/doc/openvpn-2.4.7/sample/sample-config-files/server.conf /etc/openvpn/
3. Edit the server config to contain the following topology configuration: topology subnet

Challenge

Install the provided server certificates.

Run:

cp /home/cloud_user/certs/ca.crt /home/cloud_user/certs/server.crt /home/cloud_user/certs/server.key /etc/openvpn

Challenge

Generate the required server keys.

Generate the dhparam key (this may take a few minutes):

openssl dhparam -out /etc/openvpn/dh2048.pem 2048

Generate the key for tls-auth and copy it to client:

openvpn --genkey --secret /etc/openvpn/ta.key

scp /etc/openvpn/ta.key cloud_user:/home/cloud_user/ta.key

Challenge

Make the necessary firewall and routing configurations for OpenVPN on `vpn-server`.

Run the following commands:

iptables -I INPUT -p udp --dport 1194 -j ACCEPT

iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE

iptables-save > /etc/sysconfig/iptables

sysctl -w net.ipv4.ip_forward=1

Challenge

Enable and start the OpenVPN server.

Run the following:

systemctl enable openvpn@server

systemctl start openvpn@server

Challenge

Install and configure the OpenVPN client on `vpn-client`.
On vpn-client, perform the following steps:
1. Install OpenVPN:
```
yum install y openvpn
```
1. Copy the client.conf file from /usr/share/doc:
```
cp /usr/share/doc/openvpn-2.4.7/sample/sample-config-files/client.conf /etc/openvpn/
```
1. Update the remote command hostname directive in /etc/openvpn/client.conf as follows:
```
remote vpn-server 1194
```
Challenge

Install the provided client and ca-certificates on `vpn-client`.
Copy the provided certificates off of vpn-server and to the noted directories on vpn-client with the following commands.

Run on the host vpn-client:
```
cp /home/cloud_user/ca.crt /etc/openvpn/
```
```
cp /home/cloud_user/client.key /etc/openvpn/
```
```
cp /home/cloud_user/client.crt /etc/openvpn/
```
Challenge

Install the `tls` key from `vpn-server` on `vpn-client`.

Assuming you copied the tls key over to /home/cloud_user/ta.key when you created it in the earlier tasks, run cp /home/cloud_user/ta.key /etc/openvpn/ta.key.

If not, you will need to retrieve the file from vpn-server:/etc/openvpn/ta.key.
Challenge

Enable and start the OpenVPN client.
Run the following commands:
```
systemctl enable openvpn@client
```
```
systemctl start openvpn@client
```

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