Graceful BGP Router Shutdown via Notification Subcodes
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Solution Overview
Problem
Planned shutdown or reset of BGP routers in computer networks leads to temporary outages due to immediate withdrawal of routes, causing 'black holes' in traffic service, as backup paths are not promptly propagated during convergence time, especially when the shutdown router is the best path.
Innovation Solution
A graceful shutdown technique is introduced, where a BGP router announces its intention to shut down using novel subcodes in the BGP Notification message, allowing it to maintain route validity for a 'grace period' and propagate backup paths before final withdrawal, using Administrative Graceful Router Shutdown and Administrative Graceful Router Reset subcodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a BGP router is immediately shut down or reset, then the router can be removed from service quickly, but temporary outages occur due to immediate route withdrawal causing black holes in traffic service
Solution Approach 1:
The router sends a Notification message with a new subcode indicating its intention to shut down before actually closing connections. This preliminary notification allows peer routers to prepare backup paths in advance, preventing traffic black holes when the router is fully shut down.
Solution Approach 2:
The grace period mechanism acts as a cushion between route withdrawal and actual shutdown. During this period, the router maintains route validity while peers propagate backup paths, preventing sudden traffic loss and providing a smooth transition.
2Reliability
If backup paths are propagated during convergence time, then traffic service continuity is maintained, but the convergence time is extended due to route validation and propagation delays
Solution Approach 1:
Peer routers begin propagating backup paths during the grace period before the original routes are fully withdrawn. This preliminary propagation of alternative routes reduces the actual convergence time needed after shutdown by having backup paths ready in advance.
3Reliability
If the router maintains route validity during grace period, then packet forwarding continues without loss, but network resources are consumed during the transition period
Solution Approach 1:
The router dynamically adjusts its operational state during the grace period, maintaining route validity for forwarding while simultaneously allowing peers to establish backup paths. This dynamic state transition ensures continuous service while preparing for efficient resource release after shutdown.
Data Source
AI summary
A graceful shutdown technique modifies a routing protocol to allow an intermediate node, such as a router, to announce to its peer routers (peers) its intention to be gracefully shutdown and removed from service in a network. By announcing its intention to be removed from service, the shutdown router closes (terminates) all connections with its peers and all original routes advertised on those connections are removed (withdrawn) from service. According to the inventive technique, the shutdown router may continue forwarding packets over the network for a “grace” period of time, i.e., the router maintains the validity of those original routes so that packets mapped to the routes are not dropped (at least during the grace period). The grace period also allows backup paths to be propagated to each peer and put into service prior to a final withdrawal of the shutdown router's paths from a forwarding information base of the peer. Thus, the grace period enables the network to continue using the shutdown router as a next hop as it re-converges to use the alternate, backup paths.