Imagine I need to put a SSL VPN solution in order to handle the respective load:

Up to 10,000 concurrent users in North America.

Up to 6,000 concurrent users in Europe.

Up to 3,000 concurrent users in Australia.

Requirement is that all respective employees are able to get connected to VPN in case of bad weather or other extraordinary conditions which prevent people from showing up at work.

Imagine the aforementioned Cisco SSL VPN solution handle max of 5,000 users concurrently per device. High availability is required.

Question:

How could I address this? If I put (2) SSL VPN devices in North America, that could handle 5,000 users/node. If that is an active/active configuration, do you know if I can get away with (2) nodes, or perhaps I would need (3) nodes in order to handle up to 10,000 concurrent connections?