Service Function Reverse Path Forwarding via Network Service Header
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Solution Overview
Problem
In service function chaining environments, existing technologies face challenges in enabling service functions to generate and send packets back to the source through a service function chain, as they lack the capability to determine symmetric path IDs and next service-hop indices, which are essential for reverse path forwarding.
Innovation Solution
The solution involves using Network Service Headers (NSH) with a reverse packet request bit field, OAM bits, and reserved bits to request and identify the reverse path, allowing service functions to encapsulate and forward packets back to the source by deriving or encoding reverse path information from incoming packets or control plane data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If service functions are enabled to generate and send packets back to the source through service function chaining, then reverse path forwarding capability is improved, but device complexity increases due to the need for determining symmetric path IDs and next service-hop indices
Solution Approach 1:
The patent applies preliminary action by pre-establishing symmetric path information in the forward direction. When a packet traverses the service function chain forward, the symmetric path ID and next service-hop index for the reverse direction are determined and embedded in the packet header (specifically in the NSH - Network Service Header). This allows service functions to generate reverse packets without performing complex real-time calculations, as the reverse path information is already prepared and attached during the forward traversal.
Solution Approach 2:
The patent uses the packet header (specifically the NSH - Network Service Header) as an intermediary to carry reverse path information. Instead of requiring service functions to directly compute symmetric path IDs and next service-hop indices when generating reverse packets, the forward-traversing packet serves as a mediator that transports this information through the service function chain. The NSH contains fields that store the symmetric path ID and next service-hop index, which are then used by service functions to efficiently generate and forward reverse packets.
2Ease of manufacture
If existing technologies are used for service function chaining, then deployment simplicity is maintained, but reverse path forwarding functionality is insufficient due to lack of capability to determine symmetric path IDs and next service-hop indices
Solution Approach 1:
The patent applies universality by making the NSH (Network Service Header) serve multiple functions. In addition to its standard function of carrying service path identification and forwarding information for forward packets, the NSH is enhanced to also carry symmetric path ID and next service-hop index information for reverse path forwarding. This multi-functionality allows the same data structure to support both forward packet routing and reverse packet generation, eliminating the need for separate mechanisms and maintaining deployment simplicity while enabling reverse path forwarding capability.
3Manufacturing precision
If service functions can determine symmetric path IDs and next service-hop indices, then reverse packet generation accuracy is improved, but information processing overhead increases
Solution Approach 1:
The patent applies preliminary action by determining and embedding the symmetric path ID and next service-hop index during the forward packet traversal, before reverse packet generation is needed. This eliminates the need for service functions to perform information-intensive calculations at the moment of reverse packet generation. The reverse path information is pre-computed and attached to the packet header, ensuring accuracy while minimizing real-time processing overhead.
Solution Approach 2:
The patent uses copying by extracting and copying the necessary path information from the forward packet's NSH to create the reverse packet's NSH. Instead of recalculating path information, the service function copies the pre-determined symmetric path ID and next service-hop index from the incoming packet header and uses them to construct the outgoing reverse packet. This copying approach ensures consistency and accuracy while significantly reducing processing overhead compared to recomputation.
Data Source
AI summary
Embodiments are directed to receiving an original packet at a service function; determining, for a reverse packet, a reverse service path identifier for a previous hop on a service function chain; determining, for the reverse packet, a service index for the reverse service path identifier; and transmitting the reverse packet to the previous hop on the service function chain.