Site-to-Site IKEv2 IPSec VPN using Pre-Shared Key Authentication - simple configuration example for two Cisco routers - NIL - Network Information Library
Cisco IOS VPN Configuration Guide - Site-to-Site and Extranet VPN Business Scenarios [Cisco 7200 Series Routers] - Cisco
How To Configure IPsec Site-to-Site VPN On Cisco Router? – GetLabsDone
EdgeRouter - Route-Based Site-to-Site IPsec VPN – Ubiquiti Support and Help Center