Solar wind tool reports High Transmit Traffic on vSAN uplink port.

Products

• VMware vSAN

Issue/Introduction

Symptoms:

• Solar wind monitoring tool may report below "High Transmit" errors on the uplink port configured for vSAN.

• There may be no errors on VMNIC configured for vSAN.

 

Environment

VMware vSAN (All Versions)

Cause

High TCP transmission errors such as out-of-order packets (OOO), duplicate ACKS (Dup ACKs), TCP retransmissions, etc on the TCP stack of the vSAN network can cause higher transmission rate. This can lead to a high Transmit warning on the Solar wind monitoring tool.

Below metrics can be monitored on vCenter UI>vSAN cluster>Monitor>vSAN>Support>Performance For Support>Performance Dashboard>TCP/IP

Resolution

TCP errors originate outside the ESXi stack. Engage network team or vendor to further investigate the issue.

Additional Information

There may be noticeable spikes in tcpSackRecvBlocksRate, tcpRcvDupAckRate, and tcpTxRetransmitRate, indicating potential network congestion or packet loss. These metrics suggest issues with TCP retransmissions and duplicate acknowledgments, which could be contributing to the high transmit rates.

• tcpSackRecvBlocksRate metric refers to the rate at which TCP Selective Acknowledgment (SACK) blocks are received.
• tcpRcvDupAckRate measures the rate at which the host receives duplicate TCP acknowledgments.
• tcpTxRetransmitRate represents the rate at which the host retransmits TCP segments.