Configuring Check Point NGX VPN-1/Firewall-1
Cisco ASA: All-in-one Next-Generation Firewall, IPS, and VPN Services (3rd Edition)
Cisco ASA Firewall Fundamentals - 3rd Edition: Step-By-Step Practical Configuration Guide Using the CLI for ASA v8.x and v9.x
VPNs and NAT for Cisco Networks: A CCIE v5 guide to Tunnels, DMVPN, VPNs and NAT (Cisco CCIE Routing and Switching v5.0) (Volume 3)