High Availability Licensing (HAL) is an important feature for applications that require high availability. Activating HAL introduces fault tolerance, because the licensed applications no longer depend on a single point of failure. HAL uses three license servers, each assigned a specific role. The first license server is the primary server and allows clients to both checkout and borrow licenses. The second license server can allow clients to checkout licenses only, in the event the first license server is down. The third license server denies all requests, but is required as part of the configuration to ensure high availability. To use HAL, your license must be HAL-enabled by your vendor. See Enabling and configuring HAL for information about using the web-based UI to set up HAL license servers.
HAL requires a stable network connection between the servers. Too many network problems will make the system unstable and license checkouts unreliable.
Note that a license server can serve either a HAL-enabled license or normal network license, not both.