Edge Device Fast Reroute Loop Prevention

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Solution Overview

Problem

Conventional MPLS/VPN networks experience significant latency in converging on a new network topology after a PE-CE link failure, leading to data packet loss and degradation of services like voice-over-IP and video flows.

Innovation Solution

Implementing a fast reroute (FRR) technique at the edge of the network, where edge devices reroute data packets to a backup edge device with an identifier indicating they are protected, preventing further rerouting and avoiding loops.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional MPLS/VPN networks use standard routing protocols for topology convergence, then routing updates are propagated correctly, but convergence time is significant (seconds) causing data packet loss

Engineering Contradiction:

Improveservice continuityVSAvoidconvergence time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent pre-establishes backup routing paths and backup edge devices before failures occur. When a PE-CE link fails, the network immediately switches to pre-configured backup paths rather than waiting for routing protocols to converge, achieving sub-second recovery by acting in advance on preventive measures

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces a fast reroute mechanism as an intermediary between the failure detection and full routing convergence. This fast reroute system provides immediate temporary routing decisions using backup paths while the conventional routing protocols continue their slower convergence process in the background

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If edge devices continuously reroute packets during failures, then service availability improves, but routing loops may occur

Engineering Contradiction:

Improveservice availabilityVSAvoidrouting loops

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent implements feedback mechanisms where edge devices track which packets have been rerouted using identifiers in packet headers. When a backup edge device receives a rerouted packet, it checks the identifier and suppresses further rerouting actions, preventing infinite loops while maintaining service continuity

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces continuous mechanical rerouting decisions with a state-tracking system using packet identifiers. Instead of constantly evaluating whether to reroute, the system uses the identifier to immediately recognize and suppress redundant rerouting actions, eliminating the harmful feedback loop

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS7477593B2Loop prevention techniques using encapsulation manipulation of IP/MPLS field

Publication Date: 2009.01.13 CISCO TECHNOLOGY INC

AI summary

A fast reroute (FRR) technique is implemented at the edge of a computer network. In accordance with the technique, if an edge device detects a node or link failure that prevents it from communicating with a neighboring routing domain, the edge device reroutes at least some data packets addressed to that domain to a backup edge device which, in turn, forwards the packets to the neighboring domain. The rerouted packets are designated as being “protected” (i.e., rerouted) data packets before they are forwarded to the backup edge device. To that end, the edge device incorporates an identifier into the rerouted data packets to indicate that the packets are being FRR rerouted. The identifier may be a predetermined value stored at a known location in the rerouted packets'encapsulation headers, such as in their MPLS or IP headers. Upon receiving a data packet containing the identifier, the backup edge device is not permitted to reroute the packet a second time.