Hash Collision Mitigation via PBR Entries in TCAM
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Solution Overview
Problem
Hash collisions in information handling systems, particularly in hash forwarding tables, lead to inefficient operations and packet flooding due to the inability to add new entries when collisions occur, disrupting normal switch device performance.
Innovation Solution
The implementation of a Policy Based Routing (PBR) system that generates and stores PBR entries in a Ternary Content Addressable Memory (TCAM) when a hash collision occurs, allowing for the forwarding of subsequent packets associated with the collision, thereby mitigating the disruption and enabling efficient packet forwarding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a hash forwarding table is used to forward packets efficiently, then packet forwarding speed is improved, but hash collisions occur that prevent new entries from being added
Solution Approach 1:
The patent introduces PBR entries as an intermediary mechanism between the hash forwarding table and the control plane. When a hash collision occurs, instead of failing to add the entry, the system creates a PBR entry that captures the colliding traffic and forwards it appropriately. This intermediary PBR entry system resolves the conflict between maintaining fast hash-based forwarding and reliably adding new forwarding entries.
2Object-affected harmful factors
If the hash forwarding table capacity is increased to reduce collisions, then collision frequency is reduced, but device cost and complexity increase
Solution Approach 1:
The patent changes the operational parameters of the forwarding system by introducing a secondary lookup mechanism (PBR entries) that operates alongside the hash table. Rather than increasing hash table capacity, the system modifies the forwarding process to check PBR entries when hash collisions occur, effectively managing collision frequency without expanding the primary forwarding table.
3Manufacturing precision
If software techniques are used to handle hash collisions, then forwarding accuracy is improved, but processing efficiency decreases
Solution Approach 1:
The patent segments the forwarding logic into two distinct parts: the fast path using hash-based forwarding for normal operation, and the exception handling path using PBR entries for collision resolution. This segmentation allows the majority of traffic to be processed efficiently through the hash table while only colliding packets undergo the more careful PBR lookup, maintaining overall processing efficiency while improving forwarding accuracy.
Data Source
AI summary
A hash collision mitigation system includes a source device coupled to a destination device by a networking device. The networking device receives a first packet from the source device, and uses first packet information included in the first packet to perform a hash operation on the first packet and generate a hash value. The networking device then determines that the hash value has caused a hash collision with a first hash value forwarding entry in a hash forwarding table in the networking device and, in response, generates a first Policy Based Routing (PBR) entry for the first packet. The first PBR entry is configured to provide for the forwarding of at least one second packet received from the destination device and directed to the source device, and that first PBR is stored in a Ternary Content Addressable Memory (TCAM) in the networking device.