Standby Main Control Board Adjacency for FC Switch Routing
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Solution Overview
Problem
In high-end Fabric Channel (FC) switches with a distributed structure, switching from a primary main control board to a standby main control board causes interruptions in FSPF routing forwarding due to the deletion of Link State Records (LSRs) and routing recalculations, leading to channel congestion and state fallbacks, especially during network topology changes.
Innovation Solution
The standby main control board establishes an adjacency relationship with neighbors using pre-backed-up LSRs and generates new LSRs after promotion, avoiding the deletion of existing LSRs and routing, and reduces channel congestion by not requiring immediate backup of all LSU messages and routing data, allowing for seamless transition without re-establishing the neighbor state machines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the standby main control board performs complete neighbor discovery and LSR synchronization after switching from primary to standby, then routing accuracy is ensured, but forwarding interruption time increases and productivity decreases
Solution Approach 1:
The standby main control board pre-synchronizes LSRs from the primary board before switching occurs. When switching happens, the standby already possesses current LSR data, enabling immediate routing calculation and forwarding resumption without complete neighbor rediscovery, thus maintaining routing accuracy while minimizing forwarding interruption
Solution Approach 2:
The patent allows the standby board to skip the complete neighbor discovery process and directly use pre-synchronized LSRs for routing calculation. This rushing through of essential steps (using existing LSRs immediately) reduces the time required for forwarding resumption while still ensuring accurate routing through subsequent LSR updates
2Stability of the object's composition
If the standby main control board synchronizes all LSRs from the primary board after switching, then routing consistency is improved, but channel congestion increases due to excessive data transmission
Solution Approach 1:
The patent extracts only the essential LSR data needed for routing consistency from the complete LSR set. The standby board synchronizes specific LSRs related to active neighbors and routing paths rather than all possible LSRs, reducing data transmission volume and channel congestion while maintaining sufficient routing consistency for normal operations
Solution Approach 2:
The patent applies partial synchronization by selecting and synchronizing only the necessary LSRs (those relevant to current routing) rather than performing excessive complete LSR synchronization. This partial action achieves adequate routing consistency while minimizing the harmful effect of channel congestion
3Measurement precision
If the FC switch recalculates routing from scratch after main control board switching, then routing accuracy is ensured, but time loss increases due to neighbor state machine fallback
Solution Approach 1:
The standby main control board preliminarily calculates routing based on pre-synchronized LSRs before actually taking over forwarding. This preliminary routing calculation is ready in advance, so when switching occurs, the standby can immediately resume forwarding with accurate routing without starting calculation from scratch, significantly reducing time loss
Solution Approach 2:
The patent maintains continuity of routing calculation by using the standby board's pre-calculated routing (based on pre-synchronized LSRs) immediately upon switching. This avoids the interruption caused by complete recalculation and neighbor state machine fallback, ensuring continuous useful action in routing maintenance while preserving accuracy through subsequent LSR updates
Data Source
AI summary
Calculating routing after switching occurs from a primary main control board to a standby main control board in a Fiber Channel (FC) switch includes receiving neighbor Link State Records (LSRs) sent by the primary main control board and backing up the neighbor LSRs on the standby main control board. The standby main control board is triggered to be promoted to the primary main control board, and an adjacency relationship is established with neighbors according to the backed up neighbor LSRs. LSRs of the switch are generated based on available ports on the switch and the neighbors, and a message is sent for maintaining the adjacency relationship to the neighbors with which the adjacency relationship has been established. Routing is calculated based on the neighbor LSRs and the LSRs of the switch.