2.7. Securing Virtual Private Networks (VPNs) In Red Hat Enterprise Linux 6, a Virtual Private Network ( VPN ) can be configured using the IPsec tunneling protocol which is supported by the Libreswan application. Libreswan is a fork of the Openswan application and examples in documentation should be interchangeable. The NetworkManager IPsec plug-in is called NetworkManager-openswan . Note Libreswan replaced Openswan as the preferred implementation of IPsec in Red Hat Enterprise Linux 6.8. Performing an upgrade from a version earlier than 6.8 replaces the openswan package with libreswan . Libreswan is an open-source, user-space IPsec implementation available in Red Hat Enterprise Linux 6. It uses the Internet key exchange ( IKE ) protocol. IKE version 1 and 2 are implemented as a user-level daemon. Manual key establishment is also possible via ip xfrm commands, however this is not recommended. Libreswan interfaces with the Linux kernel using netlink to transfer the encryption keys. Packet encryption and decryption happen in the Linux kernel. Libreswan uses the network security services ( NSS ) cryptographic library, which is required for Federal Information Processing Standard ( FIPS ) security compliance. 2.7.1. IPsec VPN Using Libreswan To install Libreswan , issue the following command as root . Note that the libreswan package is available from the Extras repository, which needs to be enabled for the installation to succeed. See How to enable/disable a repository using Red Hat Subscription Manager? (The ID of the Extras repository is rhel-6-server-extras-rpms .) To check that Libreswan is installed, issue the following command: After a new installation of Libreswan the NSS database should be initialized as part of the install process. However, should you need to start a new database, first remove the old database as follows: Then, to initialize a new NSS database, issue the following command as root : To start the ipsec daemon provided by Libreswan , issue the following command as root : To confirm that the daemon is now running: To ensure that Libreswan will start when the system starts, issue the following command as root : Configure any intermediate as well as host-based firewalls to permit the ipsec service. See Section 2.8, "Firewalls" for information on firewalls and allowing specific services to pass through. Libreswan requires the firewall to allow the following packets: UDP port 500 for the Internet Key Exchange ( IKE ) protocol UDP port 4500 for IKE NAT-Traversal Protocol 50 for Encapsulated Security Payload ( ESP ) IPsec packets Protocol 51 for Authenticated Header ( AH ) IPsec packets (uncommon) We present three examples of using Libreswan to set up an IPsec VPN. The first example is for connecting two hosts together so that they may communicate securely. The second example is connecting two sites together to form one network. The third example is supporting roaming users, known as road warriors in this context.

Commands:
~]# yum install libreswan
~]USD yum info libreswan
~]# rm /etc/ipsec.d/*db
~]# ipsec initnss Initializing NSS database See 'man pluto' if you want to protect the NSS database with a password
~]# service ipsec start
~]USD service ipsec status pluto (pid 3496) is running
~]# chkconfig ipsec on