In order for branch offices to connect to the network at the main office for backup purposes, a defined hierarchy must be observed when establishing the connection. Connections are only established from the "lower" to the "upper" networks, i.e. from the branch office to the switching node, from the switching node to the main office.
Thus connections only have to be accepted passively at the main office. The switching nodes also accept the branch office connections passively, but establish the connections to the main office actively. This hierarchy is a prerequisite for the later definition of VPN rules.
