# US 2011/0317548 A1 · Method of and device for recovering from a root bridge failure > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2011/0317548 A1 - Document ID: US20110317548A1 - Status: Published application - Kind: A1 - Application number: 12/874,789 - Filed: 2010-09-02 - Published: 2011-12-29 - Earliest claimed: 2010-06-29 - Assignees: Ruggedcom Inc. - Inventors: Michael Pustylnik - Web page: https://patentgrep.com/patent/US20110317548A1 ## CPC - H04L 43/0811: by checking connectivity - H04L 12/462: {LAN interconnection over a bridge based backbone} - H04L 41/06: Management of faults, events, alarms or notifications - H04L 45/02: Topology update or discovery - H04L 45/48: Routing tree calculation - H04L 45/28: using route fault recovery - H04L 45/488: using root node determination - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract An active loop-free topology established by a Rapid Spanning Tree Algorithm and Protocol (RSTP) emanates from an original root bridge. Upon a bridge directly connected to the root bridge suspecting a failure in the root bridge, the bridge directly connected to the root bridge generates a Root Failure Suspicion Notification (RFSN) Bridge Protocol Data Unit (BPDU) comprising a standard Rapid Spanning Tree (RSTP) BPDU portion and a compressed failed root identifier portion uniquely identifying the root bridge which is suspected of failing. The RFSN BPDU is propagated amongst the bridges in the network. The bridges which can identify a flag in the standard RSTP BPDU portion of the RFSN BPDU decompress the compressed failed root identifier and compare it to the stored root identifier at each bridge. If the received failed root identifier in the RFSN BPDU corresponds to the stored root identifier of the bridge, the bridge deletes the stored root identifier. The bridge then commences a time out during which, if further RFSN BPDUs are received, only the BPDU portion is acted on and the failed root identifier portion is ignored. The RSTP BPDU portion is acted on in the standard way pursuant to the RSTP protocol whether or not the bridge can also identify the flag or the compressed failed root identifier in the RFSN BPDU. Conversion to a new active topology is facilitated by deleting the original root bridge identifier which is suspected of failure from the memory of the bridges. ## Claims ### Claim 1 A method for notifying bridges connected to a network of a root bridge failure, said method comprises: (a) detecting, by at least one bridge directly connected to the root bridge, a failure in a connection to the root bridge; (b) generating, by the at least one bridge directly connected to the root bridge, a root failure suspicion notification (RFSN) bridge protocol data unit (BPDU) comprising a standard Rapid Spanning Tree BPDU portion and a failed root identifier portion uniquely identifying the root bridge which is suspected of failing; and (c) propagating the RFSN BPDU to adjacent bridges in the network. ### Claim 2 (depends on 1) A method as defined in claim 1 further comprising: (d) upon receipt of the RFSN BPDU by a receiving bridge in the network, comparing the received failed root identifier in the RFSN BPDU to a stored root identifier stored at the receiving bridge; and (e) if the root bridge identified in the failed root identifier portion corresponds to the stored root identifier, deleting the stored root identifier at the receiving bridge. ### Claim 3 (depends on 2) The method as defined in claim 2 further comprising: (f) each bridge receiving a RFSN BPDU acting on the standard BPDU portion of the RFSN BPDU whether or not the received failed root identifier corresponds to the stored root identifier; and (g) propagating the RFSN BPDU to other bridges in the network to repeat steps (d) to (g). ### Claim 4 (depends on 2) The method as defined in claim 2 further comprising: when the RFSN BPDU is generated, setting a failed root identifier (FRI) flag in the standard RST BPDU portion; and upon receipt of the RFSN BPDU by the receiving bridge, checking for the FRI flag and, if set, comparing the received failed root identifier portion to the stored root identifier at the receiving bridge. ### Claim 5 (depends on 4) The method as defined in claim 4 wherein for bridges in the network which lack the capability to identify the RFSN BPDU using Rapid Spanning Tree Algorithm and Protocol (RSTP), ignoring the failed root identifier portion and propagating the standard BPDU portion without the failed root identifier portion. ### Claim 6 (depends on 4) The method as defined in claim 4, wherein the FRI flag corresponds to the Topology Change Acknowledge flag encoded in Bit 8 of Octet 5 in the standard RST BPDU portion. ### Claim 7 (depends on 2) The method as defined in claim 2 wherein the step of generating the RFSN BPDU by at least one bridge directly connected to the root bridge further comprises: compressing the failed root identifier portion such that the RFSN BPDU consists of no more than 60 bytes; and upon receipt of the RFSN BPDU by the receiving bridge, decompressing the compressed failed root identifier to obtain the bridge identifier uniquely identifying the root bridge which is suspected of failing. ### Claim 8 (depends on 7) The method as defined in claim 7 wherein the network is an Ethernet network; and wherein each RFSN BPDU is contained within a single 60 byte Ethernet data frame. ### Claim 9 (depends on 2) The method as defined in claim 2 further comprising: after propagating the RFSN BPDU, commencing a time out period for a predetermined period of time during which the receiving bridge will ignore the failed root identifier portion of any subsequently received RFSN BPDU and will not delete the stored root identifier but will act on the standard BPDU portion and propagate the standard BPDU portion without the failed root identifier portion. ### Claim 10 In a network of bridges interconnected according to an active topology established by a Rapid Spanning Tree Algorithm and Protocol (RSTP), said active topology comprising an original loop-free topology emanating from an original root bridge, an improved method comprising: (a) detecting, at a bridge directly connected to the original root bridge in the original loop-free topology, a failure in the original root bridge; (b) generating, at the bridge directly connected to the original root bridge, a root failure suspicion notification (RFSN) bridge protocol data unit (BPDU) comprising a standard BPDU portion and a failed root identifier portion uniquely identifying the original root bridge; (c) propagating the RFSN BPDU by the bridge directly connected to the original root bridge to adjacent bridges to notify the adjacent bridges of a suspicion that the original root bridge has failed and providing standard BPDU information in the standard BPDU portion as if the original root bridge had failed to commence convergence towards a new loop-free topology with a new bridge other than the original root bridge. ### Claim 11 (depends on 10) The method recited in claim 10 further comprising: (d) upon receipt of the RFSN BPDU by a receiving bridge in the network, comparing, at the receiving bridge, the received failed root identifier portion identifying the original root bridge to a stored root identifier stored at the receiving bridge, and, (e) if they correspond, deleting, at the receiving bridge, the stored root identifier. ### Claim 12 (depends on 11) The method as recited in claim 11 further comprising: (f) each bridge receiving a RFSN BPDU acting on the standard BPDU portion of the RFSN BPDU whether or not the received failed root identifier corresponds to the stored root identifier; and (g) propagating the RFSN BPDU to other bridges in the network to repeat steps (d) to (g). ### Claim 13 (depends on 12) The method as recited in claim 12 further comprising: when the RFSN BPDU is generated, setting a failed root identifier (FRI) flag in the standard RST BPDU portion; and upon receipt of the RFSN BPDU by the receiving bridge, checking for the FRI flag and, if set, comparing the received failed root identifier portion to the stored root identifier at the receiving bridge; and wherein, for bridges in the network which lack the capability to identify the RFSN BPDU using Rapid Spanning Tree Algorithm and Protocol (RSTP), ignoring the failed root identifier portion and propagating the standard BPDU portion without the failed root identifier portion. ### Claim 14 (depends on 11) The method as defined in claim 11 wherein the step of generating the RFSN BPDU by the bridge directly connected to the original root bridge in the original loop-free topology further comprises: compressing the failed root identifier portion such that the RFSN BPDU consists of no more than 60 bytes; and upon receipt of the RFSN BPDU by the receiving bridge, decompressing the compressed failed root identifier to obtain the bridge identifier uniquely identifying the root bridge which is suspected of failing; and wherein the network is an Ethernet network, and, each RFSN BPDU is contained in a single 60-byte data frame. ### Claim 15 (depends on 11) The method as defined in claim 11 further comprising: after propagating the RFSN BPDU, commencing a time out period for a predetermined period of time during which the bridge will ignore the failed root identifier portion of any subsequently received RFSN BPDU and will not delete the stored root identifier but will act on the standard BPDU portion and propagate the standard BPDU portion without the failed root identifier portion. ### Claim 16 (depends on 1) A bridge for notifying other bridges connected to a network of a root bridge failure, said bridge comprising means to execute the method of claim 1. ### Claim 17 (depends on 1) A computer program having stored thereon instructions which, when executed by one or more processors of a bridge, cause the bridge to execute the method recited in claim 1.