[2025] Setting Up StrongSwan IPSec VPN: A Comprehensive Guide

Published: 07 January 2025
on channel: Francis Techworld
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In this video, we'll walk you through the complete process of setting up a StrongSwan VPN server on Ubuntu and configuring it to work seamlessly with SonicWall. Whether you're a network administrator or an enthusiast looking to enhance your network security, this step-by-step guide will help you get started.

What You'll Learn:
StrongSwan Installation: How to install StrongSwan and related packages on Ubuntu.
IP Forwarding: Enabling IP forwarding to allow traffic from the VPN tunnel to the internet.
NAT Configuration with iptables: Setting up NAT to translate private IP addresses of VPN clients to the public IP address of the server.
StrongSwan Configuration: Configuring StrongSwan to handle both fixed IP and dynamic IP connections.
Aggressive Mode with PSK: Modifying StrongSwan settings to enable Aggressive Mode with PSK (not recommended for security reasons).
Restarting Services: Restarting the StrongSwan service to apply new configurations.
Verification: Checking the status of IP forwarding and iptables rules to ensure everything is set up correctly.
Troubleshooting Commands: Useful commands to troubleshoot and verify your StrongSwan setup.
Commands and Settings:
1. StrongSwan Installation:

sudo apt update
sudo apt install strongswan strongswan-pki libcharon-extra-plugins libcharon-extauth-plugins libstrongswan-extra-plugins
2. IP Forwarding:

Temporarily:
sudo sysctl -w net.ipv4.ip_forward=1
Permanently:
sudo nano /etc/sysctl.conf
Add the following line:

net.ipv4.ip_forward=1
Apply the changes:

sudo sysctl -p
3. NAT Configuration with iptables:

Install iptables:
sudo apt install iptables
Add NAT Rules:
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo iptables -A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -i eth0 -o eth0 -j ACCEPT
Save iptables Rules:
sudo apt-get install iptables-persistent
sudo netfilter-persistent save
sudo netfilter-persistent reload
4. StrongSwan Configuration:

Edit ipsec.conf:
sudo nano /etc/ipsec.conf
Add the following configuration:

config setup
charondebug="ike 2, knl 2, cfg 2"
nat_traversal=yes

conn vpn-static
keyexchange=ikev2
ike=aes256-sha256-modp2048!
esp=aes256gcm16!
dpdaction=clear
dpddelay=300s
rekey=no
left=10.0.0.4
leftid=10.0.0.4
leftsubnet=10.0.0.0/24
right=208.263.110.51
rightid=208.263.110.51
rightsubnet=0.0.0.0/0
authby=secret
lifetime=28800s
auto=start
leftfirewall=yes

conn vpn-dynamic
keyexchange=ikev1
ike=aes256-sha256-modp2048!
esp=aes256gcm16!
dpdaction=restart
dpddelay=30s
dpdtimeout=120s
rekey=no
left=10.0.0.4
leftid=10.0.0.4
leftsubnet=10.0.0.0/24
right=%any
rightid=%any
rightsubnet=0.0.0.0/0
authby=secret
lifetime=28800s
auto=start
leftfirewall=yes
aggressive = yes
Edit ipsec.secrets:
sudo nano /etc/ipsec.secrets
Add the following line:

10.0.0.4 any: PSK S3rv3r#2024T3st#C@seH@ck3r$123
5. StrongSwan Configuration for Aggressive Mode with PSK:

Edit strongswan.conf:
sudo nano /etc/strongswan.conf
Add the following configuration:

charon {
load_modular = yes
plugins {
include strongswan.d/charon/*.conf
}
i_dont_care_about_security_and_use_aggressive_mode_psk = yes
}

include strongswan.d/*.conf
6. Restart StrongSwan Service:

sudo systemctl restart strongswan-starter.service
7. Verify Configuration:

Check IP forwarding:
sudo sysctl net.ipv4.ip_forward
Check iptables rules:
sudo iptables -t nat -L
sudo iptables -L
8. Troubleshooting Commands:

sudo ip xfrm policy
sudo journalctl -u strongswan-starter
sudo ipsec statusall
sudo nano /etc/ipsec.conf
sudo systemctl restart strongswan-starter.service
sudo nano /etc/ipsec.secrets
sudo nano /etc/strongswan.conf
sudo ipsec verify
ip route show table 220
By following these steps, you will have a fully functional StrongSwan VPN server integrated with SonicWall, ready to secure your network traffic. If you have any questions or need further assistance, feel free to leave a comment below!

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#VPNSetup #NetworkSecurity #StrongSwan


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