FTP session timeouts when Forwarding type used

Hello, I would like to ask how exactly is the session managed by F5 when FTP traffic is going through Forwarding type VS. I understand there is TCP idle timeout for 5 minutes, but why it get's dropped and doesn't see keep alive packets send by FTP?

 

Another question related. I managed to fix this by creating new Forwarding VS matching only FTP and disabling "Reset on Timeout". However, each article mentions that with this option disabled you need to enable "Loose Initiation". I haven't enabled this option and it's working completely fine, no more timeouts on FTP transfer of large files.

 

Can someone please explain both behaviors?

 

Update: I just realized what could be the reason that it is working without that option. We have now 2 Forwarding VSs, one general matching all and one matching FTP. Since actual FTP data are being exchanged on HIGH ports isn't it going through that default VS and only FTP control goes through FTP VS? Since LB doesn't send RESET neither client/server drops the connection, even though the control channel actually times out.

 

Does it make sense? :)

 

Thank you. Martin