Technical Tip: Set up IPsec VPN between FortiGate and Sophos XG using IKEv2

wcruvinel · ‎12-27-2023

Description

This article describes how to set up an IPsec VPN between FortiGate and Sophos XG using IKEv2.

Scope

FortiGate, IPsec VPN.

Solution

Network Diagram.

Configuration:

FortiGate.

Create IPsec phases and tunnels.

Select Next.
Under Network, set IP Version to IPv4.
Set Remote Gateway to Static IP Address.
For IP Address, enter the WAN IP address of the Sophos Firewall (for example: 10.55.3.1).
Set NAT Transversal to Disable (it can be enabled, but it must be the same on the other side.) and Dead Peer Detection to On Demand.
Under Authentication, set Method to Pre-shared Key.
Enter the Pre-shared Key.
In IKE, set Version to 2.
Under Peer Options, set Accept Types to Any peer ID.

Configure Phase 1 Parameters.

Set Encryption to AES256 and Authentication to SHA512.
Select Add and set Encryption to AES256 and Authentication to SHA384.
For Diffie-Helman Groups, select 16, 19, and 21.
For Key Lifetime, enter 5400 seconds.

Configure Phase 2 Parameters:

Under Phase 2 Selectors, enter a Name.
Set the Local Address to Subnet and enter the LAN IP address of the FortiGate appliance (for example 192.168.50.0/24).
Set the Remote Address to Subnet and enter the LAN IP address of the XG Firewall (for example 192.168.62.0/24).
Expand the Advanced section.
Under Phase 2 Proposal, set Encryption to AES256 and Authentication to SHA512.
Select Add and set Encryption to AES256 and Authentication to SHA384.
Select Enable Replay Detection and Enable Perfect Forward Secrecy (PFS).
For the Diffie-Hellman Group, select 16, 19, and 21.
For Local Port, Remote Port, and Protocol, select All.
Select Auto-negotiate.
Set Key Lifetime to Seconds and enter 3600 in Seconds.

Select OK.

Create a Static Route for the VPN Tunnel.

Go to Network -> Static Routes and select Create New.

For Destination, select Subnet and enter the LAN IP address of the XG Firewall (for example 192.168.50.0/24).
Set the Device to the IPsec tunnel created previously (for example Forti-SFIKEv2.).
For Administrative Distance, enter 10.
Set Status to Enabled.

Select OK.

Create Firewall Rules.

Enter a Name.
Set the Incoming Interface to the LAN interface of the FortiGate appliance (example: Forti-SFIKEv2).
Set the Outgoing Interface to the IPsec tunnel created (example: vlan680 (port1)).
For Source, Destination, and Service, select all.
Set the Schedule to always.

Similarly, create another firewall policy for traffic from the XG Firewall to the FortiGate appliance.

Note: Turn off NAT if NAT-T will not be used in the VPN Profile.

Select OK.

Sophos XG Firewall.

Create an IPsec Connection.

Go to Configure -> VPN -> IPsec Connections and select Add.
Under General Settings, enter a Name.
Set IP Version to IPv4, Connection Type to Site-to-Site, and Gateway Type to Respond Only.
Select Activate on Save.

Under Encryption, set Policy to IKEv2.
Set the Authentication Type to Preshared Key, enter the Preshared Key, and Repeat Preshared Key.

Under Gateway Settings -> Local Gateway set Listening Interface to the WAN IP address of XG Firewall (for example: PortE1.690 - 10.55.3.1), and set Local Subnet to LAN.
Under Gateway Settings -> Remote Gateway set Gateway Address to the WAN IP address of FortiGate appliance (for example: 10.55.4.1), and set Remote Subnet to Forti_LAN.

Create a Firewall Rule.

Go to Protect -> Firewall and select Add Firewall Rule.
Enter a Rule Name.
For Sources Zones, select LAN. For Destination Zones, select VPN.
Under Identity, clear the Match known users check box.