Performance issues when using LACP across multiple NPMs

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Article ID: 167979

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Updated On:

Products

XOS

Issue/Introduction

Performance issues when using LACP across multiple NPMsSymptoms:
  • performance degradation when using LACP bundle across multiple NPMs
  • high value of Early NFI reinjection counter in show interface detail
  • problem disappears when using only single interface or when all links in LACP bundle are attached to a single NPM 
  • tcpdump on NPMs shows that sending switch is transmitting frames for a specific uni-directional flow inconsistently over two different LACP ports 

Cause

Since each packet for a single flow may reach another NPM, the NPMs have to re-classify the flow and this is causing significant performance impact. The IEEE specification for LACP requires that all frames for a given stream must be transmitted out of a single interface. 

X-series is transmitting frames consistently out of the same interface for a specific uni-directional flow. Note that the port selection might be different for the reverse flow, i.e. each LACP station might select another link from the LACP bundle to transmit frames for that particular bi-directional flow. 

Resolution

Contact the vendor of the switch to provide a solution.

Workaround

We cannot correct this problem if the sending switch is not complying with the IEEE standard. The following workarounds may be used to mitigate the issue on LACP bundle with two links: 

- temporarily disable one of the two links in LACP or do not use LACP 
- attach both links in the LACP bundle to the same NPM on the X-series side