EVPN Backup-DF Fast Reroute During Forwarder Election
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Solution Overview
Problem
Existing EVPN architectures face challenges in quickly rerouting network traffic due to long convergence times during designated forwarder elections, leading to potential packet loss and duplication in single-active redundancy modes.
Innovation Solution
Implement a mechanism that fast-unblocks the Backup-DF interface based on redirected packets from the active DF, using a slow-path confirmation mechanism to maintain data and control plane synchronization, allowing CE-to-PE traffic to achieve minimal loss similar to PE-to-CE redirection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If designated forwarder election is performed using traditional EVPN convergence mechanisms, then network traffic can be rerouted with proper forwarding state establishment, but the convergence time is long causing packet loss and duplication
Solution Approach 1:
The patent pre-establishes backup forwarding states and designates backup designated forwarders in advance before failures occur. When a failure is detected, the pre-configured backup DF can immediately take over forwarding responsibilities without waiting for traditional election convergence, thus reducing packet loss and convergence time
Solution Approach 2:
The patent implements a feedback mechanism where the active DF monitors the operational status of backup DFs and receives status updates from them. This feedback loop ensures that when the active DF fails, the backup DF with the best operational status is already identified and ready to assume the forwarding role, enabling rapid failover while maintaining forwarding reliability
2Loss of time
If fast rerouting is implemented by unblocking Backup-DF interface, then convergence time is reduced, but data and control plane synchronization may be compromised
Solution Approach 1:
The patent uses feedback mechanisms where backup DFs report their operational status to the active DF, and the active DF provides forwarding state information to backups. This continuous feedback ensures that even during fast rerouting, all DFs maintain synchronized understanding of the network state, preventing control plane inconsistencies
Solution Approach 2:
The patent introduces a controlled information exchange mechanism as an intermediary between data plane forwarding decisions and control plane state synchronization. The EVPN control messages serve as intermediaries that carry forwarding state information between DFs, ensuring that fast rerouting does not compromise synchronization by mediating the state updates through standardized control plane protocols
3Device complexity
If single-active redundancy mode is used to prevent packet duplication, then forwarding control is simplified, but traffic loss occurs during DF election convergence
Solution Approach 1:
The patent pre-configures multiple designated forwarders with clear roles and responsibilities before failures occur. The backup DFs are pre-established with the ability to immediately assume forwarding responsibilities, eliminating the need for complex real-time election processes and preventing packet loss while maintaining simplified forwarding control through pre-defined single-active operation
Solution Approach 2:
The patent enables the network to skip the traditional lengthy DF election convergence process by having pre-identified backup DFs that can immediately take over forwarding. This rushing through the failover process by bypassing prolonged election states reduces packet loss while maintaining the simplicity of single-active redundancy through automated role transition
Data Source
AI summary
A mechanism that allows CE-to-PE traffic to achieve minimal traffic loss at the same rate as PE-to-CE redirection (FRR). The solution relies on a fast-unblocking of the Backup-DF interface based on appearance of redirected packets from the active DF-Elected peer. A slow-path confirmation mechanism is included to further mitigate false-positives, as well as maintaining data plane and control plane in sync.