Libreswan

Libreswan is an open-source implementation of IPsec and IKE protocols used to create secure VPN connections between networks, servers, and remote systems. It provides encrypted communication for site-to-site, host-to-host, and remote access VPN deployments.

The solution supports secure network communication using IPsec, IKEv1, and IKEv2 technologies. It is suitable for cloud environments, enterprise networks, secure server communication, and VPN gateway deployments on Ubuntu systems.

Version: Libreswan 5.2 (Ubuntu package version: 5.2-2.2ubuntu2)

Features of Libreswan:

• Open-source IPsec VPN implementation.
• Supports IKEv1 and IKEv2 protocols.
• Provides encrypted site-to-site and host-to-host VPN connections.
• Supports pre-shared keys, certificates, and secure authentication methods.
• Uses Linux XFRM/IPsec kernel capabilities for secure network traffic.
• Supports NAT Traversal using UDP port 4500.
• Suitable for cloud, enterprise, and hybrid network environments.

Usage instructions for Libreswan
$ sudo su -
$ ipsec --version
$ systemctl enable --now ipsec
$ systemctl status ipsec --no-pager
$ ipsec status
$ ipsec verify

Libreswan configuration files are located in:

/etc/ipsec.conf
/etc/ipsec.secrets
/etc/ipsec.d/

To verify that Libreswan is listening for IKE and NAT-T traffic, run:

ss -lunp | grep -E ':500|:4500'

For Azure deployments, ensure the required Network Security Group rules permit IPsec traffic from trusted remote VPN peers. Commonly used ports include UDP 500 for IKE and UDP 4500 for IPsec NAT Traversal.

Disclaimer: Libreswan is provided “as is” under applicable open-source licenses. Users are responsible for correctly configuring VPN peers, authentication credentials, certificates, routing, firewall rules, and Azure networking policies. This solution is suitable for secure IPsec VPN communication in development and production environments.