Technical Note: How the FortiGate behaves when asymmetric routing is enabled

http://kb.fortinet.com/kb/microsites/search.do?cmd=displayKC&docType=kc&externalId=FD39943&sliceId=1&docTypeID=DT_KCARTICLE_1_1&dialogID=27692425&stateId=1%200%2027694157

Technical Note: Building a Layer-2 VPN with VxLAN over IPsec

http://kb.fortinet.com/kb/microsites/search.do?cmd=displayKC&docType=kc&externalId=FD40170&sliceId=1&docTypeID=DT_KCARTICLE_1_1&dialogID=27692425&stateId=1%200%2027694157

Technical Note: How to setup redundant point-to-point IPSec VPN using multi-home BGP links

http://kb.fortinet.com/kb/microsites/search.do?cmd=displayKC&docType=kc&externalId=FD35166&sliceId=1&docTypeID=DT_KCARTICLE_1_1&dialogID=27692425&stateId=1%200%2027690965

Technical Note: How to configure L2TP using interface/route based IPsec VPN:

http://kb.fortinet.com/kb/microsites/search.do?cmd=displayKC&docType=kc&externalId=FD41147&sliceId=1&docTypeID=DT_KCARTICLE_1_1&dialogID=26850343&stateId=1%200%2026848963