Deterministic BIER Forwarding via Segmented Tables
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Solution Overview
Problem
The BIER forwarding method in networks with ECMP and LAGs results in non-deterministic paths, making network operations, administration, and management difficult due to inconsistent performance and out-of-order packet delivery, especially when routers join or leave multicast groups.
Innovation Solution
Creating multiple bit index forwarding tables (BIFTs) with each including a single possible next hop for destinations, and using these tables to determine next hops and equal cost multipath next hops, ensuring that paths depend on the destination and hash values, thereby stabilizing network performance and simplifying operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If BIER forwarding method is used in networks with ECMP and LAGs, then forwarding rate increases and network capacity improves, but path determinism deteriorates causing non-deterministic paths for any one destination
Solution Approach 1:
The forwarding table is segmented into multiple independent tables, each containing a single possible next hop for destinations. This segmentation allows the system to maintain multiple forwarding tables in memory simultaneously, with each table representing a deterministic path option, thereby resolving the conflict between high forwarding rate and path determinism.
Solution Approach 2:
Multiple forwarding tables are pre-computed and populated into memory before actual packet forwarding occurs. The paths are determined in advance based on destination and hash values, ensuring that during packet forwarding, the system only needs to perform simple table lookups rather than complex path calculations, thus maintaining both high forwarding rate and path determinism.
2Productivity
If BIER forwarding method is used with ECMP, then network efficiency improves, but network operations and management become difficult due to inconsistent performance
Solution Approach 1:
The system uses hash values as feedback mechanisms to select specific forwarding tables. This feedback ensures that the same packet flow consistently maps to the same forwarding table and thus the same path, providing predictable and consistent performance that simplifies network operations and management while maintaining high efficiency.
Solution Approach 2:
The invention changes the parameter of path selection from dynamic ECMP-based selection to deterministic selection based on destination address and hash value. This parameter change ensures that paths are consistent and predictable, making network operations and management easier while preserving network efficiency.
3Device complexity
If BIER forwarding method is used, then control plane processing is reduced, but packet delivery order becomes inconsistent
Solution Approach 1:
By segmenting the forwarding information into multiple tables with single next hops, the system ensures that packets within the same flow are directed through the same path. This maintains packet delivery order while keeping control plane processing simple, as the segmentation is performed during table population rather than during packet forwarding.
Data Source
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AI summary
A network device creates multiple forwarding tables, and each forwarding table includes information associated with a first set of destinations and a second set of destinations. The first set of destinations is different than the second set of destinations. The network device determines, for each forwarding table, next hops for the first set of destinations, and determines, for each forwarding table, equal cost multipath next hops for the second set of destinations. The network device populates the multiple forwarding tables with information associated with the next hops and the equal cost multipath next hops, and the multiple forwarding tables are used to forward a multicast packet toward multiple destinations.