For load-balancing FTP servers on a VS using L7 Non-Transparent there is a few special setting that need to be enabled and this can only be done for passive mode. Active mode connections are only possible in L4 or L7 Transparent mode.
For an explanation on Transparency see:
https://support.kemptechnologies.com/hc/en-us/articles/201758196-What-Does-Transparency-Mean-
For external traffic:
- On the Virtual service in Standard Options for 'Server Initiating Protocols' select 'Other Server Initiating'
- Promiscuous mode must be enabled on the FTP servers.
- Extra ports configured on the FTP server can be set in Standard options on the Virtual service
- For some FTP servers you may need to specify external IP address of Firewall to allow passive connections
FTP non-transparent VIP setting
For internal traffic:
- Promiscuous mode must be enabled on the FTP servers.
- Extra ports configured on the FTP server can be set in Standard options on the Virtual service