IPsec VPN can be simply understood as means of providing security of our critical data sent over public network. IPsec is very much secure as it uses lot of different protocols to add encryption as well as authentication.
I will not be explaining each and every components of IPSec in this particular blog but would just be demonstrating a configuration of simple IPSec VPN between 2 sites making use of Fortigate 500 E and Cisco ISR 4451. This blog only contains configuration of FortiGate in particular.
PROCESS 1
The first process is to go under VPN and then click on IPsec Wizard. We will be creating an custom IPsec profile with a name site-to-site-vpn.
PROCESS 2
We will now need to input all the parameters required for completing the VPN process. At the beginning we will be configuring for PHASE I parameters mentioning things like remote IP address which is 110.44.119.21 in our particular case. We will also be configuring things like authentication type, hashing algorithm , group, lifetime and encryption. Pre- shared key will be used for authenticating in this particular configuration. IKE Version 1 is being used.
PROCESS 3
We will now configure for PHASE II of IPsec VPN mentioning about parameters that we are going to use for Encyrption ,Authentication and also things like PFS, Anti Replay Detection etc.
Firewall policy needs to be added for both direction which you can see in the below screenshot that I have attached. The first screenshot displays traffic that is being allowed from tunnel interface (Incoming Interface) to the lan interface (Outgoing Interface). Nat will be disabled in this policy and also have not used all the other security profiles.
The second screenshot displays that traffic is being allowed from LAN Interface (SOSYS) towards the Outgoing interface (tunnel interface) .
PROCESS 5
We will now need to add the static route where the destination IP is 10.10.254.0/24 and the next hop will be the public IP of the remote router which being 110.44.119.21.
We will need to configure it same in the Cisco Router as well with exact same parameters that has been used in the Fortigate Firewall Phase I and Phase II.
Lets' now finally verify in Fortigate as well as in the Cisco Router side.
We will need to at least send an icmp request from either of the side for IPsec VPN to come up.
We can clearly see that ISAKMP PHASE I looks to be up and in the QM_IDLE state. Let's check for the PHASE II part as well.
Bravo ! The VPN Tunnel is IP and also reachable. The destination IP in our case is 172.16.0.18 which falls under SOSYS Interface of the Fortigate.
Configuring IPsec VPN in Fortigate is very simple in compared to some other firewalls and router. I will end my blog here and be writing more about VPN in my next blog.
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