GRE Tunnel Keepalive Reachability Detection
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Solution Overview
Problem
The Generic Routing Encapsulation (GRE) protocol lacks a mechanism to determine if the destination endpoint of a tunnel is reachable, leading to potential loss of traffic and inability to route packets along alternative paths due to the source endpoint considering the tunnel operational even when the destination endpoint is unreachable.
Innovation Solution
A novel technique where the source endpoint constructs and sends 'keepalive' packets, which are returned by a reachable destination endpoint, allowing the source endpoint to determine reachability by processing these packets, and setting the tunnel to a non-operational state if the destination endpoint is unreachable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the GRE protocol is used for tunneling, then packet encapsulation and transmission through intermediate networks is enabled, but the source endpoint cannot determine if the destination endpoint is reachable
Solution Approach 1:
The source endpoint performs preliminary actions by sending keepalive packets through the tunnel before actual data transmission. These packets are sent in advance to verify tunnel reachability, allowing the source to detect destination unavailability before routing actual traffic, thus preventing data loss while maintaining GRE tunneling functionality
Solution Approach 2:
The invention implements a feedback mechanism where the source endpoint sends keepalive packets and waits for their return. The absence of returned keepalive packets provides feedback indicating destination unreachability, enabling the source to dynamically adjust routing decisions. This feedback loop resolves the contradiction by providing reachability information that the original GRE protocol lacked
2Productivity
If the source endpoint considers the tunnel operational, then traffic routing through the tunnel continues, but traffic loss occurs when the destination endpoint is unreachable
Solution Approach 1:
Before routing actual traffic through the GRE tunnel, the source endpoint performs preliminary reachability verification using keepalive packets. This preliminary action ensures that the tunnel is truly operational, preventing subsequent traffic loss while maintaining continuous routing capability for valid tunnels
Solution Approach 2:
The invention applies preliminary anti-action by proactively detecting tunnel failures through keepalive packet monitoring. By detecting destination unreachability before actual data transmission, the system prevents the harmful effect of traffic loss, allowing productivity to be maintained for healthy tunnels while avoiding waste on failed routes
Data Source
AI summary
A technique that enables a source endpoint of a tunnel employing encapsulation to determine if a destination endpoint of the tunnel is reachable or unreachable. The technique issues “keepalive” packets that are returned to the source endpoint by a reachable destination endpoint. The source endpoint of the tunnel constructs a keepalive packet containing a return-keepalive packet, encapsulates it and forwards it over the tunnel to the destination endpoint. The destination endpoint, in turn, decapsulates the packet to yield the return-keepalive packet and forwards the return-keepalive packet preferably over the tunnel towards the source endpoint. Upon arrival at the source endpoint, the return-keepalive packet is processed. By receiving the return-keepalive packets the source end-point concludes the destination endpoint is reachable. After a predetermined number of return-keepalive packets have not been received, the source endpoint concludes that the destination endpoint is unreachable.