LDP-IGP Synchronization via Temporary Route Injection
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Solution Overview
Problem
Existing techniques for LDP-IGP synchronization in MPLS networks face scalability and performance issues when multiple interfaces become active simultaneously, particularly when an alternate path between routers does not exist, leading to VPN service failures and increased SPF computations.
Innovation Solution
The technique involves holding down IGP adjacency over a newly active interface while establishing a LDP adjacency, injecting a temporary route with a large administrative weight into the routing table to ensure LDP convergence, and then advertising a normal cost metric for the link to complete IGP convergence, thereby reducing VPN traffic drops and optimizing SPF computations to a single round.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If IGP convergence is performed before LDP convergence to enable IP forwarding, then network connectivity is established quickly, but VPN traffic is dropped because label bindings are not yet distributed
Solution Approach 1:
The patent applies preliminary action by holding down the IGP adjacency establishment before LDP convergence is complete. This prevents IGP from advertising the link to other routers until LDP has finished distributing label bindings, ensuring that VPN traffic will not be dropped due to premature forwarding before label availability.
2Reliability
If LDP-IGP synchronization is implemented using traditional LSA flush and SPF computation methods, then LDP convergence is ensured before IGP convergence, but scalability and performance deteriorate when many interfaces are consecutively activated
Solution Approach 1:
The patent extracts the LSA flush and SPF computation operations from the interface activation process. Instead of performing these operations for each individually activated interface, the patent batches them into a single LSA flush and single SPF computation that handles multiple interfaces simultaneously, dramatically reducing processing overhead.
Solution Approach 2:
The patent merges multiple interface activation events into a single synchronization operation. When multiple interfaces become active concurrently or in quick succession, the system combines their LSA flushes and SPF computations into one unified operation, improving scalability and router performance.
3Reliability
If IGP adjacency is held down to wait for LDP convergence, then VPN traffic drop is reduced, but an alternate reachable path must exist between the router and peer router
Solution Approach 1:
The patent introduces an intermediary mechanism in the form of a temporary static route that provides reachability to the peer router's transport address during the LDP convergence period. This static route acts as a mediator, allowing LDP packets to be exchanged while the IGP adjacency is held down, eliminating the requirement for an alternate physical path.
Data Source
AI summary
A technique may improve LDP-IGP synchronization in a MPLS network when an interface of a router coupled to a communications link along a shortest path between a source router and a destination router becomes newly active. Specifically, an IGP adjacency may be held down over the newly active link while a LDP adjacency is established over the link. The router may inject a temporary, non-redistributable route having a large administrative weight into its routing table utilizing addresses learned during establishment of the LDP adjacency. The injected route ensures that there is a reachable route to a peer router so that LDP may converge. After LDP has converged and all needed label bindings have been distributed in the MPLS network utilizing the injected route, IGP executing on the router may advertise a normal cost metric for the link associated with the newly active interface, and IGP convergence may be completed.