Can we connect VPN between a Cisco router and an RF600VPN, Lan to Lan and Client to Lan? Does the SSH Sentiel IPSec client software support Cisco's router?

Yes, you can connect VPN between an RF600VPN and Cisco router.

LAN to LAN is compatible. Client to LAN is not. You can use PPTP as a client to connect to our RF600VPN.

No, SSH Sentinel does not support Cisco. Cisco has their own IPSec client.