OSPF Designated Router Switchover Without Traffic Drops
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Solution Overview
Problem
In OSPF networks, the switchover process from a failed Designated Router (DR) to a Backup Designated Router (BDR) can take seconds or longer, leading to traffic drops due to the lack of valid network-LSA messages during the transition, especially in large-scale networks.
Innovation Solution
A method and apparatus that involve detecting DR failure, holding router-LSA refresh and flooding procedures, and using a timer to wait for BDR declaration as the working DR, allowing for seamless DR switchover by refreshing the link-state database and updating routing tables when conditions are met.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If DR-Other devices immediately refresh router-LSA and compute routes upon detecting DR failure, then route computation speed is improved, but traffic drops occur during the switchover period before BDR is declared as working DR
Solution Approach 1:
The patent applies preliminary action by having DR-Other devices detect DR failure and prepare for switchover in advance, but delaying the actual route computation and LSA refresh until the BDR is officially declared as the working DR. This timing optimization ensures that route computation occurs only when necessary, avoiding premature calculations that would cause traffic drops while maintaining fast response once the switchover condition is met.
2Reliability
If DR-Other devices hold refresh of router-LSA and flooding procedure during DR failure, then traffic continuity is maintained, but topology convergence time increases
Solution Approach 1:
The patent uses preliminary action by detecting DR failure early and holding the refresh and flooding procedures temporarily, rather than executing them immediately. This delayed execution prevents traffic drops during the critical switchover period while ensuring that topology convergence is completed efficiently once the BDR is declared as the working DR, thus optimizing both traffic continuity and convergence time.
3Reliability
If DR-Other devices continuously refresh router-LSA and perform flooding procedure, then topology convergence is achieved, but CPU and memory resource usage increases during DR switchover
Solution Approach 1:
The patent applies periodic action by conditionally executing the router-LSA refresh and flooding procedure only when the BDR is declared as the working DR, rather than continuously or immediately upon DR failure detection. This periodic execution based on specific conditions reduces unnecessary CPU and memory resource consumption during the switchover period while ensuring that topology convergence is achieved when necessary.
Data Source
AI summary
Embodiments of the present disclosure provide method and apparatus for Designated Router (DR) seamless switchover. A method performed by a network device comprises detecting a DR failure event due to a failure DR. The method further comprises detecting that the second edge device is unreachable. The method further comprises holding refresh of router-Link State Advertisements (router-LSA) in a link-state database and flooding procedure, when a Backup Designated Router (BDR) has not declared to be a working DR in an Open Shortest Path First (OSPF) network.