MPLS Service Label Loop Prevention Fast Reroute
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Solution Overview
Problem
Conventional MPLS/VPN networks experience significant latency in converging on new network topologies 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 local fast reroute technique at the edge of the network, where edge devices reroute data packets with a service label to a backup edge device, preventing further rerouting and thus avoiding loops, using a three-level MPLS label stack with a service label between IGP and VPN labels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MPLS/VPN networks use standard routing protocols to converge on new network topologies after a PE-CE link failure, then routing correctness is maintained, but convergence time increases significantly causing data packet loss
Solution Approach 1:
The patent pre-establishes backup label-switched paths (LSPs) and configures backup edge devices before failures occur. When a PE-CE link failure is detected, the backup path is immediately activated without waiting for standard routing convergence, achieving sub-second recovery while maintaining routing correctness through pre-validated backup paths
Solution Approach 2:
The patent introduces a service label as an intermediary mechanism to distinguish protected traffic requiring fast reroute from regular traffic. This service label enables the backup edge device to identify and properly handle rerouted packets, preventing loops while allowing rapid convergence without compromising routing correctness
2Speed
If edge devices rapidly reroute packets to backup edge devices upon failure detection, then convergence speed improves to sub-second levels, but loop formation may occur at the network edge
Solution Approach 1:
The service label acts as an intermediary marker that travels with rerouted packets. When a backup edge device receives a packet with the service label, it recognizes the packet as already-rerouted traffic and prevents further rerouting, thereby breaking potential loops while maintaining the fast convergence benefit
Solution Approach 2:
The service label provides feedback information to backup edge devices about the packet's reroute status. This feedback mechanism allows backup devices to make informed forwarding decisions, preventing them from inadvertently creating loops by rerouting packets that are already on backup paths
3Device complexity
If standard two-level MPLS label stacks are used for packet forwarding, then device complexity is minimized, but the ability to implement fast reroute with loop prevention is insufficient
Solution Approach 1:
The patent segments the MPLS label stack into three distinct levels: IGP labels for intra-domain routing, a service label for fast reroute identification, and VPN labels for virtual private network routing. This segmentation allows each label to serve a specific function, enabling fast reroute and loop prevention capabilities while maintaining clear separation of concerns
Solution Approach 2:
The patent adds another dimension to the traditional two-level MPLS label stack by inserting the service label between IGP and VPN labels. This dimensional expansion provides the necessary space for fast reroute functionality without disrupting the existing IGP and VPN routing frameworks, achieving versatility while controlling complexity
Data Source
AI summary
A local 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. The backup edge device identifies protected data packets as those which contain a predetermined “service” label in their MPLS label stacks. In other words, the service label is used as an identifier for packets that have been FRR rerouted. Upon receiving a data packet containing a service label, the backup edge device is not permitted to reroute the packet a second time, e.g., in response to another inter-domain node or link failure, thereby preventing loops from developing at the edge of the network.