# US 9,521,010 B2 · Diagnosing and reporting a network break > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,521,010 B2 - Document ID: US9521010B2 - Status: Granted - Kind: B2 - Application number: 14/387,585 - Filed: 2012-04-05 - Published: 2015-10-22 - Granted: 2016-12-13 - Earliest claimed: 2012-04-05 - Assignees: Schneider Electric Industries SAS - Applicants: Vijay Vallala; Alen Mehmedagic; Mark Quealy - Inventors: Vijay Vallala; Alen Mehmedagic; Mark Quealy - Web page: https://patentgrep.com/patent/US9521010B2 ## CPC - H04L 12/44: Star or tree networks - H04L 12/18: for broadcast or conference {, e.g. multicast} - H04L 41/0803: Configuration setting - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A system, method, and computer readable medium allow a cable break or other network link failure to be detected and reported. The method may include steps of periodically transmitting a packet from a root node in the network to a next node in the network; at each successive non-root node in the loop, manipulating the packet and forwarding the manipulated packet to a next successive node in the loop; when the packet is received back at the root node within a predetermined time period, reporting that the loop is intact; and when the packet is not received back at the root node within the predetermine time period, reporting that a network break has occurred. The network may conform to the STP or RSTP protocols, and may contain one or more rings possibly including dual rings. The PLC may operate as the root node, and the reporting may be done at an application level in the PLC. ## Claims ### Claim 1 A method, comprising: transmitting, from a root node in a network configured according to a spanning tree protocol, a packet to a neighboring node in the network; determining, at a non-root node in the network, if a no-forward flag in the packet has been set and setting the no-forward flag if the packet is to be forwarded over a blocked port; forwarding the packet to a next neighboring node in the network; and reporting, when the packet is received back at the root node within a predetermined time period, that the network is intact or reporting, when the packet is not received back at the root node within the predetermined time period, that a break in the network has occurred. ### Claim 2 (depends on 1) The method of claim 1, wherein the spanning tree protocol is Rapid Spanning Tree Protocol. ### Claim 3 (depends on 1) The method of claim 1, wherein the packet has a multicast destination MAC address. ### Claim 4 (depends on 1) The method of claim 1, wherein at least one of a plurality of non-root nodes in the network forwards the packet over a blocked port. ### Claim 5 (depends on 1) The method of claim 1, wherein if a no-forward flag has been set, preventing further forwarding of the packet over a blocked port. ### Claim 6 (depends on 1) The method of claim 1, wherein if a HostMAC address in the packet matches a HostMAC address of the root node that sent the packet, the packet will be discarded. ### Claim 7 (depends on 1) The method of claim 1, wherein reporting that a break has occurred comprises generating an application-level message. ### Claim 8 (depends on 1) The method of claim 1, further comprising the step of repeating the steps on a periodic basis. ### Claim 9 (depends on 1) The method of claim 1, wherein the root node comprises a programmable logic controller (PLC) in an industrial automation system. ### Claim 10 (depends on 1) The method of claim 1, further comprising the step of preventing forwarding of the packet to a node located in a secondary ring. ### Claim 11 An apparatus comprising: a processor; and a memory storing instructions that, when executed by the processor, cause the apparatus to: receive a packet from a root node in a network configured according to a spanning tree protocol; determine if a no-forward flag in the packet has been set; set the no-forward flag if the packet is to be forwarded over a blocked port; and forward the packet to a next neighboring node in the network. ### Claim 12 (depends on 11) The apparatus of claim 11, wherein the spanning tree protocol is Rapid Spanning Tree Protocol. ### Claim 13 (depends on 11) The apparatus of claim 11, wherein the packet has a multicast destination MAC address. ### Claim 14 (depends on 11) The apparatus of claim 11, wherein the apparatus is configured to forward the packet over a blocked port. ### Claim 15 (depends on 14) The apparatus of claim 14, wherein when the packet is forwarded over the blocked port, the apparatus sets a flag in the packet to indicate that it should not be further forwarded over another blocked port. ### Claim 16 (depends on 11) The apparatus of claim 11, wherein the apparatus is configured to determine whether the no-forward flag has been set in the packet and, if the no-forward flag has been set, prevent further forwarding of the packet over a blocked port. ### Claim 17 (depends on 11) The apparatus of claim 11, wherein the apparatus is configured to discard the packet if a HostMAC address in the packet matches a HostMAC address of the apparatus. ### Claim 18 (depends on 11) The apparatus of claim 11, wherein the root node comprises a programmable logic controller (PLC) in an industrial automation system. ### Claim 19 A non-transitory computer-readable medium having stored thereon instructions that, when executed, cause an apparatus to: receive a packet from a root node in a network configured according to a spanning tree protocol; determine if a no-forward flag in the packet has been set; set the no-forward flag if the packet is to be forwarded over a blocked port; and forward the packet to a next neighboring node in the network.