1. A method for use in a cluster system, for accessing from an internet network a network server within one or a plurality of clusters, each cluster being identified by a single cluster public Internet Protocol (IP) address, said cluster system comprising a plurality of network servers organized in one of a plurality of clusters and a network load balancer system for selecting a destination network server in a cluster, each cluster comprising one or a plurality of identical network servers, said network load balancer system being connected on one hand to an access routing device and on another hand to said plurality of network servers through a private network server subnet, said method comprising the steps of: at initialization time, on each network server: defining, as a non-advertising alias, in an interface table, the public IP address of each cluster to which the network server belongs; upon reception, by the network load balancing system, of a datagram, said datagram comprising an IP header including a destination IP address field and a medium access control (MAC) header including a destination MAC address field: selecting a destination network server within the cluster corresponding to the cluster public IP address identified in the destination IP address field of the datagram IP header; replacing the destination medium access control (MAC) address field of the datagram MAC header by the MAC address of the selected destination network server; and sending the datagram through the private network server subnet, using the MAC address of the selected destination network server; and upon reception, by the destination network server, of the datagram sent by the network load balancing system: identifying the MAC address in the destination MAC address field of the datagram MAC header as being the MAC address of the selected destination network server; and processing the IP datagram if the identified cluster public IP address in the destination IP address field of the datagram IP header, is defined as a non-advertising alias in the interface table of the destination network server.