TTL Decrement in Overlay Network Encapsulation
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Solution Overview
Problem
Overlay networks, particularly L2 overlays, face challenges in preventing loops when a host moves locations, as they lack a hop-count or TTL field, leading to potential infinite looping until control plane intervention, which hinders fast convergence and local repair requirements.
Innovation Solution
The technique involves maintaining and decrementing the TTL value of an IP transport header across decapsulation and re-encapsulation operations, ensuring that packets are eventually discarded and loops are broken, even for L2 payloads without a TTL field, by re-encapsulating with a new TTL value less than the original, preventing infinite looping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If split-horizon techniques are used to prevent loops in L2 overlay networks, then loop prevention is achieved, but fast convergence and local repair capability are hindered
Solution Approach 1:
The patent introduces a TTL (Time-To-Live) parameter into the L2 overlay network frame structure. This parameter change enables loop detection and prevention through TTL expiration, allowing the network to maintain split-horizon for loop prevention while enabling fast convergence through local repair capabilities, as packets can now be redirected with updated TTL values without creating infinite loops
2Device complexity
If L2 overlay networks use traditional Ethernet frame headers without TTL field, then simplicity is maintained, but infinite looping occurs when hosts move locations
Solution Approach 1:
The patent embeds a TTL field within the L2 overlay frame structure, effectively nesting the loop-prevention mechanism inside the existing frame format. This allows the simple Ethernet-like frame structure to be maintained at the outer level while incorporating the TTL functionality at an inner level, thus achieving both simplicity and loop prevention
Solution Approach 2:
The TTL field acts as an intermediary element between the simple L2 frame structure and the required loop prevention mechanism. It provides the necessary hop-count tracking capability without fundamentally changing the L2 frame format, enabling loop detection while preserving the simplicity of the underlying Ethernet-like structure
3Stability of the object's composition
If multiple nodes are updated upon host move in distributed system, then network consistency is maintained, but convergence time exceeds tens of milliseconds requirement
Solution Approach 1:
The patent implements preliminary action by pre-configuring the TTL field in frame headers before host movement occurs. When a host moves, the source node can perform local repair by updating the TTL and redirecting frames immediately without waiting for multiple nodes to be updated, thus achieving fast convergence while maintaining network consistency through the TTL-based loop prevention mechanism
Data Source
AI summary
In one embodiment, a device receives a payload encapsulated in an Internet Protocol (IP) transport header having a time-to-live (TTL) value, and decapsulates the payload while maintaining the TTL value. In response to determining that a destination of the payload is not attached to the device, the device may then re-encapsulate the payload in a new IP transport header with a new TTL value that is less than the maintained TTL value, and transmits the re-encapsulated payload toward the destination. In this manner, loops in overlay networks may be prevented based on eventual expiration of the TTL value of the IP transport header, accordingly.