# US 7,609,618 B1 · Dynamically controlling HSRP preemption dependent on stateful NAT convergence > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,609,618 B1 - Document ID: US7609618B1 - Status: Granted - Kind: B1 - Application number: 11/303,555 - Filed: 2005-12-15 - Granted: 2009-10-27 - Earliest claimed: 2005-12-15 - Assignees: Cisco Technology, Inc. - Inventors: Kaushik Biswas; Ian Wilson; Siva Jayasenan; Sepehr Safari - Web page: https://patentgrep.com/patent/US7609618B1 ## CPC - H04L 45/28: using route fault recovery - H04L 45/583: {Stackable routers} - H04L 45/851: Dynamic network selection or re-selection, e.g. after degradation of quality - G06F 11/2028: {eliminating a faulty processor or activating a spare} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) ## Abstract The invention relates to a method for switchover from an active node to a standby node wherein when a standby network node restarts, designation of the standby node as a new active node is delayed according to 1) the period of a delay timer and 2) a counter indicating the number of data messages the standby node will be receiving from the active network node. The active node sends a notification to the standby node identifying a number of data messages that the active network node needs to send to the standby node. The standby node stores the number in a counter and decrements the counter upon receiving data messages. When the delay timer expires, the standby network node transitions to become the new active node only when the counter has reached zero. If the counter is not yet zero, then the switchover delay timer is restarted and the cycle repeats. ## Claims ### Claim 1 A method of controlling switchover from an active network node to a standby network node, comprising: when the standby network node restarts, delaying designation of the standby node as a new active node according to the period of a delay timer; receiving from the active network node a notification identifying a number of data messages that the active network node needs to send to the standby node; storing the number in a counter; receiving the data messages and decrementing the counter as the messages are received; when the delay timer expires, determining if the counter has reached zero, and transitioning the standby network node as the new active node only when the counter has reached zero; wherein the method is performed by one or more computer systems. ### Claim 2 (depends on 1) The method of claim 1 wherein a value of the delay timer is established before the standby network node restarts. ### Claim 3 (depends on 1) The method of claim 1 wherein the notification identifying a number of data messages is sent by the active node in response to a request for network address translation data contained in the active network node. ### Claim 4 (depends on 3) The method of claim 3 further comprising: responding to the request for data information by preventing creation of any new data information until the request for data is complete. ### Claim 5 (depends on 1) The method of claim 1 wherein if the counter has not yet reached zero then re-setting the delay timer for an additional period of time. ### Claim 6 (depends on 1) The method of claim 1 wherein if the counter has reached zero then the standby node sends a complete message to the active node. ### Claim 7 (depends on 6) The method of claim 6 wherein the active node permits creation of new data in response to receiving said complete message. ### Claim 8 (depends on 1) The method of claim 1 wherein transitioning the standby network node as the new active node is performed by HSRP state transition logic. ### Claim 9 (depends on 1) The method of claim 1 wherein the transitioning of the standby network node as the new active node also results in the transitioning of the active node as the new standby node. ### Claim 10 A machine-readable volatile or non-volatile medium storing one or more sequences of instructions for controlling switchover from an active network node to a standby network node, wherein execution of the one or more sequences of instructions by one or more processors causes: when the standby network node restarts, delaying designation of the standby node as a new active node according to the period of a delay timer; receiving from the active network node a notification identifying a number of data messages that the active network node needs to send to the standby node; storing the number in a counter; receiving the data messages and decrementing the counter as the messages are received; when the delay timer expires, determining if the counter has reached zero, and transitioning the standby network node as the new active node only when the counter has reached zero. ### Claim 11 (depends on 10) A machine-readable volatile or non-volatile medium as recited in claim 10 wherein a value of the delay timer is established before the standby network node restarts. ### Claim 12 (depends on 10) A machine-readable volatile or non-volatile medium as recited in claim 10 wherein the notification identifying a number of data messages is sent by the active node in response to a request network address translation for data contained in the active network node. ### Claim 13 (depends on 12) A machine-readable volatile or non-volatile medium as recited in claim 12 wherein execution of the one or more sequences of instructions by one or more processors further causes: responding to the request for data information by preventing creation of any new data information until the request for data is complete. ### Claim 14 (depends on 10) A machine-readable volatile or non-volatile medium as recited in claim 10 wherein if the counter has not yet reached zero then re-setting the delay timer for an additional period of time. ### Claim 15 (depends on 10) A machine-readable volatile or non-volatile medium as recited in claim 10 wherein if the counter has reached zero then the standby node sends a complete message to the active node. ### Claim 16 (depends on 15) A machine-readable volatile or non-volatile medium as recited in claim 15 wherein the active node permits creation of new data in response to receiving said complete message. ### Claim 17 (depends on 10) A machine-readable volatile or non-volatile medium as recited in claim 10 wherein transitioning the standby network node as the new active node is performed by HSRP state transition logic. ### Claim 18 (depends on 10) A machine-readable volatile or non-volatile medium as recited in claim 10 wherein the transitioning of the standby network node as the new active node also results in the transitioning of the active node as the new standby node. ### Claim 19 An apparatus comprising: one or more processors; one or more sequences of instructions stored in a volatile or non-volatile medium for controlling switchover from an active network node to a standby network node, which instructions, when executed by the one or more processors, are operable to: when the standby network node restarts, delay designation of the standby node as a new active node according to the period of a delay timer; receive from the active network node a notification identifying a number of data messages that the active network node needs to send to the standby network node; store the number in a counter; receive the data messages and decrement the counter as the data messages are received; when the delay timer expires, determine if the counter has reached zero, and transition the standby network node as the new active node only when the counter has reached zero. ### Claim 20 (depends on 19) The apparatus of claim 19, wherein the one or more sequences of instructions further comprise instructions which, when executed by the one or more processors, are operable to establish the value of the delay timer before the standby network node restarts. ### Claim 21 (depends on 19) The apparatus of claim 19, wherein the one or more sequences of instructions further comprise instructions which, when executed by the one or more processors, are operable to: send a request for network address translation data that is contained in the active network node; and receive the notification identifying the number of data messages from the active network node in response to the request. ### Claim 22 (depends on 21) The apparatus of claim 21, wherein the instructions operable to send the request for the network address translation data are further operable to cause the active network node to respond to the request by preventing creation of any new network address translation data until the data messages are received. ### Claim 23 (depends on 19) The apparatus of claim 19, wherein the one or more sequences of instructions further comprise instructions which, when executed by the one or more processors, are operable to re-set the delay timer for an additional period of time if the counter has not yet reached zero. ### Claim 24 (depends on 19) The apparatus of claim 19, wherein the one or more sequences of instructions further comprise instructions which, when executed by the one or more processors, are operable to send a complete message to the active network node if the counter has reached zero. ### Claim 25 (depends on 24) The apparatus of claim 24, wherein the instructions operable to send the complete message are further operable to cause the active network node to permit creation of new network address translation data in response to the complete message. ### Claim 26 (depends on 19) The apparatus of claim 19, wherein the instructions operable to transition the standby network node as the new active node are included in HSRP state transition logic. ### Claim 27 (depends on 19) The apparatus of claim 19, wherein the instructions operable to transition the standby network node as the new active node are further operable to cause the active network node to transition as a new standby node.