Configure IPsec on Linux Machine (2024)

Install Libreswan

1. Run the following commands as root:

   CODE

   yum -y updateyum -y install libnss3-dev libnspr4-dev pkg-config libpam0g-dev libcap-ng-dev libcap-ng-utils libselinux1-dev libcurl4-nss-dev flex bison gcc makeyum install wget

2. Install Libreswan:

   CODE

   yum install libreswan

3. Start the IPsec service and enable the service to be started:

   CODE

   systemctl enable ipsec

4. Configure the firewall to allow 500 and 4500/UDP ports for the IKE, ESP, and AH protocols by adding the IPsec service:

   CODE

    #firewall-cmd --add-service="ipsec"# firewall-cmd --runtime-to-permanent

   See Also

   Ports Used for IPSec

Initialize the NSS Database

1. Use the following commands to remove the old database:

   CODE

   ~]# systemctl stop ipsec

   CODE

   ~]# rm /etc/ipsec.d/*db

2. Enable IPsec:

   CODE

   systemctl enable ipsec

   

   Libreswan requires the firewall to allow the following packets: UDP port 500 and 4500 for the Internet Key Exchange (IKE) protocol. Protocol 50 for Encapsulated Security Payload (ESP) IPsec packets. Protocol 51 for Authenticated Header (AH) IPsec packets (uncommon).

3. Check IPsec status:

   CODE

   $ipsec setup status

   

4. Initialize the new NSS database, run the following command as root:

   CODE

   ~]# ipsec initnss

   

Create Host-to-Host VPN

1. Go to the/etc/ipsec.d/ directory and create a new my_host-to-host.conf file.

2. Edit the file, and enter all the details shown below:

   

   It is mandatory to maintain the gap of one tab between conn mytunnel and auto=start.

   CODE

   conn mytunnel auto=start keyexchange=ike phase2=esp pfs=no type=tunnel authby=secret leftid=(Domain name/ip of linux machine) left=(ip address of linux machine) right=(ip address of Windows machine) rightid=(Domain name of Windows machine)

   For example, see the screenshot below:
   

   

   Setting	Value
   Connection name	mytunnel
   leftid	10.1.0.127 (Linux machine)
   right	10.1.22.59 (Windows machine)
   rightid	Rinkitest.QA.schq.secious.com (FQDN domain name of Windows machine)

3. Go to the /etc folder, and make the following edits in the ipsec.secrets file:

   CODE

   (ip adddress of linux machine)<space>( ip address of windows machine)<space> : <space>PSK<space>"Shared key which we passed for Windows machine"

   

4. Start the IPsec service:

   CODE

   systemctl start ipsec

5. Verify the tunnel is up and running:

   CODE

   ipsec auto --add mytunnel

   

   

   If you receive any error message after running the above command, you have entered the incorrect values in either your host-to-host.conf file or your ipsec.secrets file. You will need to go back and enter the correct values.

6. Restart the IPsec service:

   CODE

   systemctl restart ipsec

7. You have completed configuring IPsec between Windows and Linux machines.

8. You can verify that traffic is coming in properly and is encrypted by using Wireshark: