Internet Key Exchange for IPsec VPNs Configuration Guide, Cisco IOS XE Fuji 16.9.x - VRF-Aware IPsec [Cisco ASR 1000 Series Aggregation Services Routers] - Cisco
Learn how to configure IPSEC site to site vpn on cisco router using cisco Packet Tracer – Learn Linux CCNA CCNP CEH CISSP CISA Penetration-Testing Bug Bounty IPv6 Cyber-Security Network-Security Online
Open Source Routing GRE over IPSec with StrongSwan and Cisco IOS-XE – techbloc.net