OSPF Aggregation Router Hash Signature Verification

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Solution Overview

Problem

In networks using OSPF routing protocol with route aggregation, a single link failure can cause sub-optimal routing or routing black holes due to incomplete routing information and reduced redundancy.

Innovation Solution

Establishing a 'virtual' neighbor adjacency between aggregating routers to share and compare hash signatures of aggregate addresses, allowing for the exchange of complete component lists only when hash signatures mismatch, thereby maintaining minimal information exchange and ensuring optimal routing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If address aggregation is performed by ABRs to reduce routing table size and network traffic, then routing table size and link state database size are reduced, but loss of information about optimal paths occurs resulting in suboptimal routing

Engineering Contradiction:

Improverouting table sizeVSAvoidoptimal path information

Core Design Contradiction:

Quantity of substanceVSLoss of information

Solution Approach 1:

The patent embeds hash signatures within link state advertisements (LSAs) that are already being flooded throughout the OSPF domain. The hash signatures are nested within the existing LSA structure, allowing additional information to be carried without creating separate communication channels or significantly increasing message size. This enables routers to verify optimal path information while maintaining the benefits of address aggregation.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The patent implements a feedback mechanism where routers use hash signatures to verify whether aggregated routes represent optimal paths. When suboptimal routing is detected through hash signature verification, the system can trigger route optimization by flooding specific LSAs to update routing information. This feedback loop allows the network to self-correct suboptimal routing while maintaining aggregation benefits.

Inventive Principle:

Principle #23Feedback

2Reliability

If complete component lists are exchanged between aggregating routers to prevent suboptimal routing, then optimal routing is maintained, but bandwidth usage and information exchange increase significantly

Engineering Contradiction:

Improverouting optimalityVSAvoidbandwidth usage

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent extracts only the essential verification information (hash signatures) from the complete component lists and exchanges only these condensed representations between aggregating routers. The hash signatures serve as compact fingerprints that allow verification of route optimality without requiring exchange of full routing tables or complete component lists, dramatically reducing bandwidth consumption while maintaining routing reliability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent transforms the complete component lists into hash signatures, changing the parameter representation from detailed routing information to condensed verification data. This parameter transformation reduces the size of exchanged information from potentially thousands of route entries to small hash values, enabling efficient verification of routing optimality with minimal bandwidth usage.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If address aggregation is performed to scale OSPF to large domains, then OSPF impact on CPU and memory is reduced, but routing failures or black holes can occur due to incomplete routing information

Engineering Contradiction:

ImproveOSPF scaling capabilityVSAvoidrouting failure prevention

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent performs preliminary verification of route optimality by computing and exchanging hash signatures before routing decisions are made. Aggregating routers pre-calculate hash signatures for their aggregated routes and flood them throughout the domain. This preliminary action allows other routers to verify optimality in advance, preventing routing failures and black holes before they occur while maintaining the scalability benefits of address aggregation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces hash signatures as an intermediary mechanism that bridges the gap between address aggregation and routing reliability. The hash signatures act as mediators that carry verification information without requiring complete routing table exchange, enabling routers to detect and prevent routing failures while maintaining the scalability of aggregated routing in large OSPF domains.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS7808927B2Technique to automatically deaggregate an optimum set to prevent suboptimal routing or routing failures within a link state flooding domain

Publication Date: 2010.10.05 CISCO TECHNOLOGY INC

AI summary

In one embodiment, information is signaled between aggregating routers indicating the components of aggregated addresses. This information is used to dynamically leak, or deaggregate, specific parts of the aggregated address space to reduce sub-optimal routing and possibly prevent routing black holes from occurring in a network.