Technical Tip: How to enable IKE debugging with various debug levels using a bitmask to isolate specific types of information for troubleshooting IKE negotiation failures

[akileshc]

Description	This article describes how to enable and capture debug information for troubleshooting IKE negotiation failures on a FortiGate device. IKE debugging can be useful in identifying configuration errors, negotiation failures, and issues related to NAT-T, DPD, and key exchanges during IPsec VPN setup.
Scope	FortiGate.
Solution	Debug Levels and Information: FortiGate offers various debug levels using a bitmask to isolate specific types of information. The following are the available debug information levels: diag debug application ike «debug-level» IKE debug with appropriate filters: diag debug reset diag debug console timestamp enable diag vpn ike log filter clear diag vpn ike log filter dst-addr4 <ip.of.remote.peer>       <- Remote peer IP filter. diag debug application ike -1                               <- Enable all levels of IKEd debug. diag debug application fnbamd -1                            <- Only for cert. auth and Xauth/EAP. diag debug console no-user-log-msg enable                   <- Disable writing on the console. diag debug duration <munites> diag debug enable Starting from FortiOS 7.4.1, the command to filter logs related to specific Remote Peer IP has been changed to diag vpn ike log filter rem-addr4 <ip.of.remote.peer>      These steps will enable IKE debugging on the FortiGate device to capture detailed information related to IKE negotiation failures, certificate authentication, NAT-T issues, and other related factors. The debug output can then be analyzed to identify and resolve VPN negotiation problems.