IPv6 Longest Prefix Match Using Disjoint TCAM Segmentation

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Solution Overview

Problem

Existing Longest Prefix Match algorithms designed for IPv4 do not scale well for IPv6 due to its 128-bit address space, leading to high latency and high costs, especially when using TCAM or trie-based methods.

Innovation Solution

Implementing a combination of TCAMs to separate disjoint and non-disjoint forwarding rules, with disjoint rules stored in an unordered TCAM for efficient insertion and deletion, and non-disjoint rules in an ordered TCAM, allowing for parallel searches and sub-trie lookups to minimize latency and power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If trie-based LPM lookup is used for IPv6, then lookup accuracy is maintained, but latency increases and scalability deteriorates

Engineering Contradiction:

Improvelookup accuracyVSAvoidlookup latency

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent segments the IPv6 address space by separating disjoint prefixes (stored in TCAM) from non-disjoint prefixes (stored in ordered memory structures). This segmentation allows the system to use fast parallel TCAM lookup for disjoint prefixes while using more memory-efficient structures for non-disjoint prefixes, thereby reducing overall lookup latency while maintaining accuracy for both cases.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an intermediary classification mechanism that categorizes prefixes into disjoint and non-disjoint groups before lookup. This intermediary step enables the system to apply different lookup strategies appropriate to each category, optimizing both speed and memory usage without compromising lookup accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Speed

If TCAM is used for IPv6 LPM lookup, then lookup speed is improved, but cost and power consumption increase

Engineering Contradiction:

Improvelookup speedVSAvoidhardware cost

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The patent segments the prefix storage system into two parts: disjoint prefixes stored in TCAM for fast lookup, and non-disjoint prefixes stored in ordered memory structures. This segmentation reduces TCAM size requirements and associated costs while maintaining high lookup speed for the majority of disjoint prefixes.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies different storage qualities to different prefix types: TCAM (high-speed, expensive) for disjoint prefixes where speed is critical, and ordered memory (lower-cost) for non-disjoint prefixes. This local quality differentiation optimizes the balance between cost and performance.

Inventive Principle:

Principle #3Local quality

3Productivity

If unordered TCAM is used for disjoint rules, then insertion and deletion efficiency is improved, but lookup complexity increases

Engineering Contradiction:

Improverule update efficiencyVSAvoidlookup complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent segments the prefix set into disjoint and non-disjoint categories, allowing unordered storage for disjoint prefixes in TCAM (simplifying insertion/deletion) while using ordered structures for non-disjoint prefixes. This segmentation isolates the complexity management to specific prefix types.

Inventive Principle:

Principle #1Segmentation

4Ease of manufacture

If IPv4 LPM algorithms are used for IPv6, then implementation simplicity is maintained, but scalability deteriorates

Engineering Contradiction:

Improveimplementation simplicityVSAvoidscalability

Core Design Contradiction:

Ease of manufactureVSAdaptability or versatility

Solution Approach 1:

The patent segments the IPv6 address space handling by separating disjoint and non-disjoint prefixes, adapting the IPv4 TCAM-based approach for the larger IPv6 space while maintaining implementation simplicity through familiar TCAM operations for the disjoint portion.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent addresses IPv6's larger address space by adding a dimensional separation between disjoint and non-disjoint prefixes, allowing the system to scale to IPv6's 128-bit space while reusing IPv4-era TCAM technologies for the disjoint portion.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS8798066B2Method for IPv6 longest prefix match

Publication Date: 2014.08.05 EXTREME NETWORKS INC

AI summary

IPv6 longest prefix match lookups are implemented by splitting disjoint forwarding rules from non-disjoint forwarding rules and storing these forwarding rules in separate TCAMs. When an IPv6 address is received, the full IP address is passed to the TCAM containing the disjoint forwarding rules and the first n bits of the IP address are passed to the TCAM containing the non-disjoint forwarding rules. If a hit is received in the TCAM containing the disjoint forwarding rules, a result of the hit is used to implement a forwarding decision and the search in the TCAM containing the non-disjoint forwarding rules is terminated. If no hit is obtained from the disjoint TCAM, the search result of the non-disjoint TCAM is used. If a continue flag is set in the result received from the disjoint TCAM, a sub-trie based lookup is implemented based on the remaining m bits of the IPv6 address.