Longest Prefix Match Sub-Trie Deduplication Across VRFs

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Solution Overview

Problem

Network devices face challenges in efficiently utilizing the limited capacity of LPM tables due to duplicate entries across different VRF instances, which limits the number of ACL rules that can be implemented, especially in high-end switches and routers.

Innovation Solution

Implementing LPM sub-trie deduplication techniques to avoid duplicate entries in LPM tables by reusing existing entries for duplicate sub-tries, thereby optimizing the capacity of LPM tables.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If LPM tables store duplicate entries across different VRF instances, then ACL rules can be implemented for all VRF instances, but the capacity of LPM tables is wasted and the prefix summarization scale is limited

Engineering Contradiction:

ImproveACL rule implementation across VRF instancesVSAvoidLPM table capacity utilization

Core Design Contradiction:

Adaptability or versatilityVSQuantity of substance

Solution Approach 1:

The patent merges duplicate LPM sub-tries across different VRF instances by identifying and reusing common sub-tries. When a sub-trie is found to be identical across multiple VRF instances, the system reuses the same physical LPM table entries for all VRF instances, thereby eliminating redundancy and improving capacity utilization while maintaining support for all VRF instances.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent implements multi-functionality by enabling LPM table entries to serve multiple VRF instances simultaneously. Through the deduplication mechanism, a single LPM entry can be universally reused across different VRF instances that share common prefix structures, allowing the table to perform multiple functions (supporting multiple VRF instances) with fewer physical entries.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Productivity

If LPM tables are physically enlarged to accommodate more entries, then more ACL rules can be stored, but the device complexity and cost increase

Engineering Contradiction:

Improvenumber of ACL rules that can be implementedVSAvoidphysical size of LPM tables

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent combines the storage requirements for multiple VRF instances by merging their LPM sub-tries. Instead of allocating separate physical space for each VRF instance's LPM entries, the system identifies and merges common sub-tries across instances, thereby reducing the total physical size needed while maintaining the ability to store and process ACL rules for all instances.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent uses logical copying rather than physical duplication. Instead of creating separate physical LPM entries for each VRF instance, the system creates logical references or copies that point to shared physical entries. This allows multiple VRF instances to access the same physical LPM table space without requiring actual physical duplication of entries.

Inventive Principle:

Principle #26Copying

Data Source

PatentUS20250293977A1Prefix Summarization Scale By Deduplicating Longest Prefix Match (LPM) Sub-Tries

Publication Date: 2025.09.18 ARISTA NETWORKS INC

AI summary

Techniques for improving the prefix summarization scale of the longest prefix match (LPM) tables of a network device are provided. In one set of embodiments, these techniques involve deduplicating sub-tries of LPM trie data structures that the network device uses to program LPM entries into the LPM tables. This sub-trie deduplication avoids the creation of duplicate LPM entries in the LPM tables across different virtual routing and forwarding (VRF) instances, thereby increasing the LPM tables' effective capacity.