# US 8,543,669 B2 · Network switch and method of preventing IP address collision > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,543,669 B2 - Document ID: US8543669B2 - Status: Granted - Kind: B2 - Application number: 12/058,204 - Filed: 2008-03-28 - Published: 2008-10-09 - Granted: 2013-09-24 - Earliest claimed: 2007-04-06 - Assignees: Samsung Electronics Co., Ltd. - Applicants: Won-Woo Chae; Gui-Jung Lee - Inventors: Won-Woo Chae; Gui-Jung Lee - Web page: https://patentgrep.com/patent/US8543669B2 ## CPC - H04L 61/5046: Resolving address allocation conflicts; Testing of addresses (testing when self-assigning an address H04L61/5092) - H04L 61/103: across network layers, e.g. resolution of network layer into physical layer addresses or address resolution protocol [ARP] - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A network switch and a method of preventing an IP address collision is provided. When a new node tries to use an IP address, which is being used in one broadcast domain, it is possible to detect and prevent an IP address collision in real-time, disconnect only the new node which caused the IP address collision, and quickly resolve network environment to the original state that existed prior to the collision, in order to prevent communication breakdown without the use of an additional device. ## Claims ### Claim 1 A network switch comprising: a collision detector for broadcasting a first Address Resolution Protocol (ARP) request message, received by a port of the network switch, to a broadcast domain, and if a first ARP reply message, transmitted to a source Media Access Control (MAC) address of the first ARP request message, is received, for storing the source MAC address in a collision list; and a collision manager, which stores collision MAC addresses, for comparing a destination MAC address of a packet with a MAC address of the network switch if the packet is not the first ARP request message and the source MAC address is included in the collision list, for transmitting the first ARP reply message, including the MAC address of the network switch, to an originating node of the packet if the destination MAC address of the packet is not equal with the MAC address of the network switch, and for dropping the packet if the destination MAC address of the packet is equal with the MAC address of the network switch. ### Claim 2 (depends on 1) The network switch according to claim 1, wherein the collision detector, if the first ARP reply message is not received, determines whether or not the source MAC address, included in the first ARP request message, is present in the collision list, and deletes the source MAC address from the collision list. ### Claim 3 (depends on 1) The network switch according to claim 1, wherein the collision manager, if the destination MAC address of the packet is not equal to the MAC address of the network switch, acquires an Internet Protocol (IP) address corresponding to the destination MAC address of the packet, and transmits the first ARP reply message, including the MAC address of the network switch, to an offending node, which has the source MAC address of the packet. ### Claim 4 (depends on 3) The network switch according to claim 3, wherein the collision manager acquires the IP address corresponding to the destination MAC address by at least one of using an ARP cache. ### Claim 5 (depends on 3) The network switch according to claim 3, wherein the collision manager acquires the IP address corresponding to the destination MAC address by transmitting a specified ARP request message and then receiving a specified ARP reply message. ### Claim 6 (depends on 3) The network switch according to claim 3, wherein the offending node transmits a packet by setting the MAC address of the network switch, included in the ARP reply message, as a receiving MAC address. ### Claim 7 (depends on 1) The network switch according to claim 1, further comprising a collision resolver, which broadcasts a second ARP request message, for including a MAC address of a defending node, to the broadcast domain if the first ARP reply message is received in response to the first ARP request message. ### Claim 8 (depends on 7) The network switch according to claim 7, wherein the collision resolver drops the first ARP reply message received from the defending node. ### Claim 9 (depends on 7) The network switch according to claim 7, wherein the collision resolver generates a Simple Network Management Protocol (SNMP) trap message, including address collision information, and transmits the SNMP trap message to the broadcast domain. ### Claim 10 (depends on 7) The network switch according to claim 7, wherein the collision resolver sets a filtering of the port, which received the first ARP request message, in relation to the MAC address, included in the first ARP request message, to prevent the packet from being transmitted, via the port which received the first ARP request message, to other ports. ### Claim 11 (depends on 1) The network switch according to claim 1, further comprising: a MAC address table for storing the MAC address and port information included in the first ARP request message; and an ARP cache for storing MAC addresses and IP addresses, wherein the collision list stores a MAC address of a first node for which the first ARP reply message in response to the first ARP request message is received. ### Claim 12 A network switch comprising: a collision detector for broadcasting a first ARP request message, received by a first port of the network switch, to a broadcast domain, and if a first ARP reply message in response to the first ARP request message is received, for storing a source MAC address of the first ARP request message in a collision list; a collision manager for comparing a destination MAC address of a packet, received from a network, with a MAC address of the network switch if a source MAC address of the received packet is a collision MAC address, for transmitting the first ARP reply message, including the MAC address of the network switch, to an offending node if the destination MAC address of the received packet is not equal with the MAC address of the network switch, and for dropping the received packet if the destination MAC address of the received packet is equal with the MAC address of the network switch; and a collision resolver for broadcasting a second ARP request message, including a MAC address of a defending node, to the broadcast domain if the first ARP reply message is received, to resolve the MAC address of the defending node by the neighbor node. ### Claim 13 (depends on 12) The network switch according to claim 12, wherein the collision resolver sets a filtering of the first port in relation to the MAC address of the offending node, to prevent a packet, received from the offending node, from being transmitted from the first port to other ports. ### Claim 14 A method of preventing an address collision, comprising: receiving a packet from a network; upon a determination that the packet received from the network is a first ARP request message, transmitting the packet to a broadcast domain; upon a determination that a first ARP reply message is received, storing a source MAC address of the packet in a collision list; upon a determination that the packet received from the network is not the first ARP request message, determining whether the source MAC address of the packet is present in the collision list; upon a determination that the source MAC address of the packet is present in the collision list, comparing a destination MAC address of the packet with a MAC address of a network switch; upon a determination that the destination MAC address of the packet is not equal with the MAC address of the network switch, transmitting the first ARP reply message, including the MAC address of the network switch, to an offending node, to set the destination node of the packet as the MAC address of the network switch; and upon a determination that the destination MAC address of the packet is equal with the MAC address of the network switch, dropping the packet. ### Claim 15 (depends on 14) The method according to claim 14, further comprising: upon a determination that the first ARP reply message is not received, determining whether the source MAC address, included in the first ARP request message, is present in the collision list; and upon a determination that the source MAC address, included in the first ARP request message, is present in the collision list, deleting the source MAC address from the collision list. ### Claim 16 (depends on 14) The method according to claim 14, comprising: storing the source MAC address, included in the first ARP request message; receiving port information in a MAC address table by MAC address learning; upon a determination that the first ARP reply message is not received, storing the source MAC address in an ARP cache; and upon a determination that the source MAC address is present in the collision list, deleting the source MAC address from the collision list. ### Claim 17 (depends on 14) The method according to claim 14, further comprising: upon a determination that the source MAC address of the packet is not equal with the MAC address of the network switch, acquiring an IP address, corresponding to the destination MAC address of the packet, by using at least one of an ARP cache. ### Claim 18 (depends on 14) The method according to claim 14, further comprising: upon a determination that the source MAC address of the packet is not equal with the MAC address of the network switch, acquiring an IP address, corresponding to the destination MAC address of the packet, by using a specified ARP reply message, which is received in response to a specified ARP request message transmitted to the network. ### Claim 19 (depends on 14) The method according to claim 14, further comprising: upon a determination that the first ARP reply message is received, transmitting the first ARP request message, including a MAC address of a defending node, to the broadcast domain to resolve the MAC address of the defending node by a neighbor node; and dropping a second ARP reply message received form the defending node. ### Claim 20 (depends on 14) The method according to claim 14, further comprising: upon a determination that the first reply message is received, setting a filtering of a port, which received the packet, in relation to the MAC address of the offending node. ### Claim 21 A method of preventing an address collision, comprising: receiving a packet from a network; upon a determination that the packet received from a network is a first ARP request message: transmitting the packet to a broadcast domain; determining whether a first ARP reply message is received; and upon a determination that the first ARP reply message is received, storing a source MAC address of the first ARP request message in a collision list; upon a determination that the packet received from the network is not the first ARP request message and a source MAC address of the packet is present in the collision list: comparing a destination MAC address of the packet with a MAC address of a network switch; upon a determination that the destination MAC address of the packet is not equal with the MAC address of the network switch, transmitting the first ARP reply message, including the MAC address of the network switch, to an offending node, which transmitted the packet; and upon a determination that the destination MAC address of the packet is equal with the MAC address of the network switch, dropping the packet; and upon a determination that the first ARP reply message is received: broadcasting a second ARP request message, including a MAC address of a defending node, to the broadcast domain, to resolve the MAC address of the defending node by a neighbor node; and setting a filtering of a port, which received the first ARP request message, in relation to a MAC address of the offending node. ### Claim 22 (depends on 21) The method according to claim 21, wherein the broadcasting of the second ARP request message, including a MAC address of a defending node, to the broadcast domain, comprises: generating an SNMP trap message, including address collision information; and transmitting the SNMP message to the broadcast domain.