You're viewing the documentation for the experimental version of Vagrant (the 1.x series). The current stable series is 1.0.x and the documentation can be found here. You can learn more about the Vagrant versioning scheme here.
Configuration key: config.ssh.max_tries
Default value: 100
This is the maximum number of tries that Vagrant will attempt to connect via SSH to the VM to determine when it is ready to communicate. Once this threshold is reached, then commands such as vagrant up will error saying that SSH on the VM never became ready.