# US 7,609,658 B2 · Method and system for identifying instability or a spanning tree protocol loop in a network > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,609,658 B2 - Document ID: US7609658B2 - Status: Granted - Kind: B2 - Application number: 11/498,599 - Filed: 2006-08-03 - Published: 2008-02-07 - Granted: 2009-10-27 - Earliest claimed: 2006-08-03 - Assignees: Cisco Technology, Inc. - Inventors: Muhammad Sarosh Niazi; Muhammad Moizuddin - Web page: https://patentgrep.com/patent/US7609658B2 ## CPC - H04L 12/4625: {Single bridge functionality, e.g. connection of two networks over a single bridge} - H04L 45/02: Topology update or discovery - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract Methods and systems for identifying instability or a loop in a network. In one method, a first BPDU message is received at a switch indicating a topology change. The message includes a bridge identifier identifying a network device originating the first BPDU message. A second BPDU is generated at the switch and includes the bridge identifier identifying the network device originating the first BPDU message. The method further includes transmitting the second BPDU message indicating the topology change from the switch. ## Claims ### Claim 1 A method for identifying instability or a loop in a network, comprising: receiving at a switch a first Bridge Protocol Data Unit (BPDU) message indicating a topology change, said first message including a bridge identifier identifying a network device originating said first BPDU message; generating a second BPDU message at the switch, said second BPDU message comprising said bridge identifier identifying the network device originating said first BPDU message; and transmitting from the switch said second BPDU message indicating said topology change and comprising said bridge identifier identifying the network device originating said first BPDU message; wherein the switch and the network device are not root bridges. ### Claim 2 (depends on 1) The method of claim 1 wherein the BPDU is a Topology Change Notification (TCN) BPDU. ### Claim 3 (depends on 1) The method of claim 1 wherein the BPDU is a Rapid Spanning Tree Protocol (RSTP) BPDU with a topology change flag set. ### Claim 4 A method for identifying instability or a loop in a network, comprising: receiving at a root bridge a plurality of Bridge Protocol Data Unit (BPDU) messages each indicating a topology change and comprising a bridge identifier identifying a network device originating a BPDU message upon detection of a topology change, at least a portion of said plurality of BPDU messages comprising the same bridge identifier; and identifying a source of the instability or loop by identifying the network device associated with the bridge identifier contained in a majority of said plurality of BPDU messages received at the root bridge. ### Claim 5 (depends on 4) The method of claim 4 wherein identifying a source comprises utilizing a show command to identify the number of TCN messages received at the root bridge from an originating network device. ### Claim 6 (depends on 4) The method of claim 4 wherein said BPDU messages are RSTP BPDU messages. ### Claim 7 (depends on 4) The method of claim 4 wherein said bridge identifier is a media access control address of the network device originating said BPDU message. ### Claim 8 (depends on 4) The method of claim 4 further comprising tracking TCN information at the root bridge. ### Claim 9 (depends on 4) The method of claim 4 further comprising: tracking the number of BPDU messages received per said bridge identifier; and generating an alarm if said number reaches a predetermined level. ### Claim 10 An apparatus for identifying instability or a loop in a network, comprising: a processor; and a memory that stores instructions for execution by the processor, said instructions comprising: code that processes a first Bridge Protocol Data Unit (BPDU) message indicating a topology change, said first message including a bridge identifier identifying a network device originating said message; and code that transmits a second BPDU message indicating said topology change, wherein said second BPDU message comprises said bridge identifier identifying the network device originating said first BPDU message; wherein the network device is not a root bridge. ### Claim 11 (depends on 10) The apparatus of claim 10 wherein the BPDU is a TCN BPDU. ### Claim 12 (depends on 10) The apparatus of claim 10 wherein the BPDU is an RSTP BPDU with a topology change flag set. ### Claim 13 An apparatus for identifying instability or a loop in a network, comprising: a processor operable to process at a root bridge a plurality of Bridge Protocol Data Unit (BPDU) messages each indicating a topology change and comprising a bridge identifier identifying a network device originating a BPDU message upon detection of a topology change, at least a portion of said plurality of BPDU messages comprising the same bridge identifier, and identify a source of the instability or loop by identifying the network device associated with the bridge identifier contained in a majority of said plurality of BPDU messages received at the root bridge; and a memory that at least temporarily stores information from said plurality of BPDU messages, said information including one or more addresses, each of said one or more addresses corresponding to said bridge identifier identifying the network device originating said BPDU message upon detection of a topology change. ### Claim 14 (depends on 13) The apparatus of claim 13 wherein said plurality of BPDU messages are TCN BPDUs and further comprising a TCN tracker configured to track said TCN BPDUs received at the root bridge and the address of the originating network device. ### Claim 15 (depends on 13) The apparatus of claim 13 wherein said BPDU messages are RSTP BPDU messages. ### Claim 16 A computer program product for identifying instability or a loop in a network, said computer program product comprising: code that processes a first Bridge Protocol Data Unit (BPDU) message indicating a topology change, said first message including a bridge identifier identifying a network device originating said message; code that transmits a second BPDU message indicating said topology change, wherein said second BPDU message comprises said bridge identifier identifying the network device originating said first BPDU message; and a computer-readable medium that stores the codes; wherein the network device is not a root bridge. ### Claim 17 An apparatus for identifying instability or a loop in a network, comprising: means for receiving at a switch, a first Bridge Protocol Data Unit (BPDU) message indicating a topology change, said first message including a bridge identifier identifying a network device originating said first BPDU message; means for generating a second BPDU message at the switch, said second BPDU message comprising said bridge identifier identifying the network device originating said first BPDU message; and means for transmitting from the switch said second BPDU message indicating said topology change and comprising said bridge identifier identifying the network device originating said first BPDU message; wherein the switch and the network device are not root bridges. ### Claim 18 (depends on 17) The apparatus of claim 17 wherein the BPDU is a TCN BPDU. ### Claim 19 (depends on 17) The apparatus of claim 17 wherein the BPDU is an RSTP BPDU with a topology change flag set. ### Claim 20 An apparatus for identifying instability or a loop in a network, comprising: means for receiving at a root bridge a plurality of Bridge Protocol Data Unit (BPDU) messages each indicating a topology change and comprising a bridge identifier identifying a network device originating a BPDU message upon detection of a topology change, at least a portion of said plurality of BPDU messages comprising the same bridge identifier; and means for identifying a source of the instability or loop by identifying the network device associated with the bridge identifier contained in a majority of said plurality of BPDU messages received at the root bridge. ### Claim 21 (depends on 20) The apparatus of claim 20 further comprising means for tracking TCN information at the root bridge. ### Claim 22 (depends on 20) The apparatus of claim 20 further comprising: means for tracking the number of BPDU messages received per said bridge identifier; and means for generating an alarm if said number reaches a predetermined level.