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Technical Tip: Site-to-Site VPN Configuration Master Record

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November 14, 2025
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Description	This article describes the list of consolidated Site-to-Site VPN configuration files for FortiGate devices, and applies to environments where multiple FortiGates are connected through Site-to-Site VPN tunnels and require centralized documentation for configuration management and reference purposes.
Scope	FortiGate, Site-to-Site VPN.
Solution	References from the Community Portal. Basic Configuration Guides. Technical Tip: Site to Site VPN - FortiGate to SonicWall Technical Tip: Supported Versions for Site-to-Site IPsec VPN between Microsoft Azure and FortiGate Technical Tip: FortiGate Site-to-Site VPN with Strongswan on Ubuntu Technical Tip: How to configure VPN Site to Site between FortiGates (Using VPN Setup Wizard) Technical Tip: Site-to-Site VPN Between FortiGate and SonicWall using DDNS Technical Tip: How to setup IPsec VPN between FortiGate and Cisco Routers Technical Tip: Set up IPsec VPN between FortiGate and Sophos XG using IKEv2 Technical Tip: Configuring IPSec tunnel between FortiGate and Palo Alto Technical Tip: Configuring Site-to-site IPSec VPN in Central SNAT mode with overlapping subnets Advanced Configuration and Integration. Technical Tip: Authentication with remote LDAP via site-to-site VPN Technical Tip: Dial-up IPsec traffic forwarding to site to site IPsec tunnel Technical Tip: DNAT through site to site VPN on one side of tunnel for securing original Destination IP Technical Tip: How to access remote resource over site to site IPsec tunnel for SSL VPN user Technical Tip: How to integrate remote authentication server via Site to Site VPN Technical Tip: How to let the FortiGate access internal DNS through site-to-site IPsec VPN Technical Tip: How to make sure the FortiGate will act as a responder in site-to-site IPsec VPN Technical Tip: Route-based IPsec site to site redundant VPN failover using BGP Technical Tip: U-turn traffic from SSL VPN to IPsec site-to-site tunnel Traffic and Routing Behavior. Technical Tip: Broadcast traffic over site-to-site IPsec VPN Technical Tip: IPsec VPN: Site-to-Site tunnel monitor Technical Tip: IPSec site to site VPN showing random 10.0.0.0/8 range Technical Tip: Multicast traffic over site-to-site IPsec VPN with PIM Sparse Mode Technical Tip: Site-to-Site IPsec VPN cannot establish in asymmetric routing scenario when tunnel interface is bounded to a loopback interface Technical Tip: Use of Black hole route in site to site IPsec VPN scenarios Troubleshooting and Diagnostics. Technical Tip: IPsec site-to-site VPN tunnel instability when local-in policy blocks IKE traffic Technical Tip: IPSec site-to-site VPN tunnel’s phase 2 is down due to ‘error calculating auth information’ Troubleshooting Tip: BGP peering is not established after setting up Site to Site VPN tunnel between Azure firewall and on-premise FortiGate Troubleshooting Tip: IPSec site-to-site VPN between FortiGate and Sonicwall fails with error message "ignoring unencrypted INVALID-COOKIE" Troubleshooting Tip: IPsec site-to-site tunnel between FortiGate and Barracuda firewall not getting established due to 'malformed message' Technical Tip: VPN4 ,VPN6 and EVPN Address Family for BGP in FortiOS Troubleshooting Tip: how to resolve BGP issue: 'Outgoing [RIB] Withdraw: Can't find route' Technical Tip: Dynamic routing (BGP) over IPsec tunnel Technical Tip: BGP Prefix Withdrawn entries in BGP logs Troubleshooting Tip: Site-to-Site VPN failed to establish between FortiGate and ZYXEL with cookie xxxxxxxxxxxxxxxx/0000000000000000 Troubleshooting Tip: Troubleshooting IPsec Site-to-Site Tunnel Connectivity From the Document Library. FortiOS v7.4.9: FortiGate to FortiGate. Basic site-to-site VPN with pre-shared key Site-to-site VPN with digital certificate Site-to-site VPN with overlapping subnets GRE over IPsec Policy-based IPsec tunnel FortiOS v7.4.9: FortiGate to Third Party. IKEv2 IPsec site-to-site VPN to an AWS VPN gateway IPsec VPN to Azure with virtual network gateway IPsec VPN to an Azure with virtual WAN IPSec VPN between a FortiGate and a Cisco ASA with multiple subnets Cisco GRE-over-IPsec VPN FortiOS v7.6.4: FortiGate to FortiGate. Basic site-to-site VPN with pre-shared key Basic site-to-site VPN with digital certificate Site-to-site VPN with overlapping subnets GRE over IPsec Policy-based IPsec tunnel Post-Quantum Cryptography for IPsec key exchange FortiOS v7.6.4: FortiGate to Third Party. IKEv2 IPsec site-to-site VPN to an AWS VPN gateway IPsec VPN to Azure with virtual network gateway IPsec VPN to an Azure with virtual WAN IPSec VPN between a FortiGate and a Cisco ASA with multiple subnets Cisco GRE-over-IPsec VPN