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.