We have a site to site VPN connection to a branch office. Once in a while the connection drops for some reason and then we receive an error like this on the Fortigate 310b
ike Negotiate ISAKMP SA Error: ike 3:20b27f143b809b23/0000000000000000:0: no SA proposal chosen
It is a struggle to re-establish the connection, and I only manage it through trial and error. My question now is, how can I debug this further? I'm aware of the CLI command
diag debug application ike -1 diag debug enable
This gives me the above mentioned error, but this error seems to be thrown for a number of reasons, and I can't figure out for which one exactly. We already lost a lot of time with those problems, and I need to learn to debug and troubleshoot those issues to the core, otherwise I'm lost.
Any help greatly appreciated.