VPN tunnel between two devices Firepower2110 and cisco 5520

[synthia.louis-brice]

How To Configure A Site-To-Site VPN Between FirePower 2110 and Cisco ASA 5520. 2110 inside and 5520 as the outside

[Sheraz.Salim]

here this document will give you a good start ASA and FTD. for FTD just change the interface to inside when setting up the VPN.