IP address duplication detection method using address resolution protocol

An IP address duplication detection method using an address resolution protocol in a network system in which an IP address duplication diagnosis/detection host and a plurality of check target hosts are connected to a single LAN, comprising the steps of:

• inputting a check target IP address of the same subnet as for the IP address duplication diagnosis/detection host to the IP address duplication diagnosis/detection host, and sending out an ARP request packet from the IP address duplication diagnosis/detection host;
• setting the IP address duplication diagnosis/detection host in a wait state for an ARP reply packet as a response packet for the ARP request packet immediately after the ARP request packet is sent out;
• determining the presence/absence of a response by the ARP reply packet at the time of expiration of the wait state;
• terminating the processing upon determining the absence of an IP address matching the check target IP address on the check target hosts if a result of the determination of the presence/absence of a response indicates the absence of a response, and determining the number of ARP reply packets received if the result indicates the presence of a response by the ARP reply packet;
• and
• normally terminating the processing upon determining that one host has the check target IP address in the LAN, if a result of the determination of the number indicates that one ARP reply packet is received, and completing the IP address duplication diagnosis/detection upon determining that not less than two hosts have duplicate check target IP addresses in the LAN, if the result indicates not less than two ARP reply packets are received.

An IP address duplication detection method using an address resolution protocol in a network system in which an IP address duplication diagnosis/detection host and a plurality of check target hosts are connected to a single LAN, all the hosts are respectively assigned MAC addresses as hardware addresses unique to devices without any duplication, and an address resolution protocol aimed at acquiring a MAC address of a remote device from an IP address is installed in each host, comprising the steps of:

• uniquely determining a host address range by inputting a subnet address of the same subnet as for the IP address duplication diagnosis/detection host to the IP address duplication diagnosis/detection host;
• extracting one IP address from the determined host address range;
• executing a search for all IP addresses in the corresponding range without any duplication/omission;
• terminating processing if no IP address is present in execution of the search;
• inputting, if an IP address is present, the extracted IP address as a check target IP address of the same subnet as for the IP address duplication diagnosis/detection host to the IP address duplication diagnosis/detection host, and sending out an ARP request packet from the IP address duplication diagnosis/detection host, setting the IP address duplication diagnosis/detection host in a wait state for an ARP reply packet as a response packet for the ARP request packet immediately after the ARP request packet is sent out, determining the presence/absence of a response by the ARP reply packet at the time of expiration of the wait state, terminating the processing upon determining the absence of an IP address matching the check target IP address on the check target hosts if a result of the determination of the presence/absence of a response indicates the absence of a response, and determining the number of ARP reply packets received if the result indicates the presence of a response by the ARP reply packet, and normally terminating the processing upon determining that one host has the check target IP address in the LAN, if a result of the determination of the number indicates that one ARP reply packet is received, and completing the IP address duplication diagnosis/detection upon determining that not less than two hosts have duplicate check target IP addresses in the LAN, if the result indicates not less than two ARP reply packets are received;
• managing each of states including “no assigned IP address”, “normal IP address assignment”, and “IP address duplication” as an assigned state result of each input IP address in the form of a list in a database in correspondence with each input IP address;
• and
• managing an assigned state of an unchecked IP address by executing the same detection processing on the basis of database management on an overall subnet level.