You have the following limitations when you are clustering the SSL VPN servers:
All SSL VPN servers must be running the high bandwidth version of SSL VPN.
All members of an SSL VPN cluster should belong to only one type. For example, all the members of a cluster should be either an ESP-enabled Novell SSL VPN or a Traditional Novell SSL VPN. You cannot have a cluster where some members are ESP-enabled Novell SSL VPNs and some are Traditional Novell SSL VPNs.
In the HTTPS mode, you cannot have a cluster of SSL VPNs where some servers are installed on a separate machine and some servers are installed along with the Identity Server.