An IP-address distribution system comprising: a network formed by a plurality of Ethernet switches (3 to 8, 23 to 26, 34 to 36); and a plurality of IP-address distribution devices (1, 2, 15, 16, 21, 22, 31, 32, 33, 41, 42) connected to the network, wherein: - the Ethernet switches are grouped into two or more groups, - at least one IP-address distribution device is connected to a sub-network which is a network formed by Ethernet switches in a same group, and - a terminal (9 to 12, 27 to 29, 37 to 39), operating as a DHCP-client, requests allocation of an IP-address via an IP-address request signals, - one of the Ethernet switches (4, 7, 24, 25, 34 to 36), having a physical port (13, 14) connected to another Ethernet switch in another group, is adapted to interrupt, at the physical port (13, 14), only: ∘ IP-address request signals, the IP-address request signals transmitted from the terminal (9 to 12, 27 to 29, 37 to 39); and ∘ IP-address distribution signals, the IP-address distribution signals transmitted from the at least one IP-address distribution device to the terminal in response to the IP-address request signal, by interrupting signals on the logical ports 67 and 68. a network formed by a plurality of Ethernet switches (3 to 8, 23 to 26, 34 to 36); and a plurality of IP-address distribution devices (1, 2, 15, 16, 21, 22, 31, 32, 33, 41, 42) connected to the network, wherein: - the Ethernet switches are grouped into two or more groups, - at least one IP-address distribution device is connected to a sub-network which is a network formed by Ethernet switches in a same group, and - a terminal (9 to 12, 27 to 29, 37 to 39), operating as a DHCP-client, requests allocation of an IP-address via an IP-address request signals, - one of the Ethernet switches (4, 7, 24, 25, 34 to 36), having a physical port (13, 14) connected to another Ethernet switch in another group, is adapted to interrupt, at the physical port (13, 14), only: ∘ IP-address request signals, the IP-address request signals transmitted from the terminal (9 to 12, 27 to 29, 37 to 39); and ∘ IP-address distribution signals, the IP-address distribution signals transmitted from the at least one IP-address distribution device to the terminal in response to the IP-address request signal, by interrupting signals on the logical ports 67 and 68. - the Ethernet switches are grouped into two or more groups, - at least one IP-address distribution device is connected to a sub-network which is a network formed by Ethernet switches in a same group, and - a terminal (9 to 12, 27 to 29, 37 to 39), operating as a DHCP-client, requests allocation of an IP-address via an IP-address request signals, - one of the Ethernet switches (4, 7, 24, 25, 34 to 36), having a physical port (13, 14) connected to another Ethernet switch in another group, is adapted to interrupt, at the physical port (13, 14), only: ∘ IP-address request signals, the IP-address request signals transmitted from the terminal (9 to 12, 27 to 29, 37 to 39); and ∘ IP-address distribution signals, the IP-address distribution signals transmitted from the at least one IP-address distribution device to the terminal in response to the IP-address request signal, by interrupting signals on the logical ports 67 and 68. ∘ IP-address request signals, the IP-address request signals transmitted from the terminal (9 to 12, 27 to 29, 37 to 39); and ∘ IP-address distribution signals, the IP-address distribution signals transmitted from the at least one IP-address distribution device to the terminal in response to the IP-address request signal,