VPN

A virtual private network (VPN) extends a private network across a public network and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network. The benefits of a VPN include increases in functionality, security, and management of the private network. It provides access to resources inaccessible on the public network and is typically used for telecommuting workers. Encryption is common, although not an inherent part of a VPN connection.

— Wikipedia 2022/01/07 16:40

The cluster is behind a VPN, controlled by RU. The VPN requires a RU sleep account (e.g. sleep.yourname) provisioned by RU. The VPN software can be downloaded from portal.ru.is after authenticating with the username and password.