TCAM Flow Rule Merging for Accurate Overlapping Traffic Statistics
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Solution Overview
Problem
The limited scalability of router hardware in measuring traffic flow statistics due to the constraint that each TCAM bank can only increment the counter of a single ACL rule, despite packets potentially matching multiple rules, necessitates a method to reduce the number of TCAM banks required for accurate flow statistics collection.
Innovation Solution
A system and method that identifies overlapping flow specifications, determines corresponding rules, and assigns priorities to store these rules in router forwarding tables, allowing multiple ACL rules to be added to a single TCAM bank, thereby minimizing the number of TCAM banks needed by converting flow specifications into a graph and reducing edges to match hardware limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple ACL rules are programmed into different TCAM banks to collect statistics of overlapping flows, then flow statistics measurement accuracy is improved, but the number of TCAM banks increases
Solution Approach 1:
The patent merges multiple ACL rules that match overlapping flows into a single TCAM bank by introducing intersection rules. Instead of distributing rules across multiple TCAM banks, the system combines them in one bank with priority-based matching, where intersection rules (representing overlapping flow intersections) are placed before original flow rules to ensure accurate counting of packets matching multiple flows.
Solution Approach 2:
The patent segments the ACL rule set into original flow rules and intersection rules. Intersection rules are created to represent the intersection of multiple overlapping flows, and these segmented rules are then prioritized and placed in the TCAM bank to accurately capture packets belonging to multiple flows simultaneously.
2Reliability
If ACL rules are distributed across multiple TCAM banks, then packets matching multiple flows can be counted accurately, but hardware resource requirements increase
Solution Approach 1:
The patent combines multiple ACL rules into a single TCAM bank by creating intersection rules that represent overlapping flow intersections. These intersection rules are prioritized and placed before original flow rules in the same TCAM bank, allowing accurate counting of packets matching multiple flows without requiring multiple separate TCAM banks.
3Device complexity
If the number of TCAM banks is reduced to minimize hardware usage, then device complexity is reduced, but the ability to accurately measure overlapping flow statistics deteriorates
Solution Approach 1:
The patent segments ACL rules into original flow rules and intersection rules. Intersection rules are specifically created to represent the intersection of multiple overlapping flows and are placed in the TCAM bank with higher priority. This segmentation ensures that packets matching multiple flows are correctly counted by the intersection rules before being matched by original flow rules.
Solution Approach 2:
The patent changes the priority parameter of ACL rules, assigning higher priority to intersection rules than to original flow rules. This parameter change ensures that when packets match multiple flows, the intersection rule (representing the overlapping portion) is matched first, allowing accurate differentiation between packets belonging to single flows versus those belonging to multiple flows.
Data Source
AI summary
Overlapping flow rules are included in a ternary content addressable memory (TCAM), while still enabling a hardware counter to increment each of the overlapping rules when a packet matching each of the overlapping rules is transmitted through the TCAM. In a given set of flow specifications, a first flow specification is identified that overlaps with a second flow specification. Rules are determined corresponding to the first flow specification, the second flow specification, and an intersection of the first and second flow specifications. Priorities are assigned to each of the rules, wherein the rule corresponding to the intersection is assigned a higher priority than the rules corresponding to the first and second flow specifications. Such rules are stored in the TCAM.