Configuring Flow Control on VMware ESXi and VMware ESX

Products

VMware vSphere ESXi

Issue/Introduction

This article provides methods for disabling flow control on physical network interfaces used by an ESXi/ESX host.

Pause Frames are related to Ethernet flow control and are used to manage the pacing of data transmission on a network segment. Sometimes, a sending node (ESXi/ESX host, switch, and so on) may transmit data faster than another node can accept it. In this case, the overwhelmed network node can send pause frames back to the sender, pausing the transmission of traffic for a brief period of time.

If flow control is undesired in an environment, the support for flow control can be disabled for a given network interface or driver on the ESX/ESXi hosts. The method differs for different drivers.

Environment

VMware ESXi 6.x/7.x/8.x
VMware vSphere ESXi 6.x/7.x/8.x

Resolution

Configuring flow control using driver module options

ESXi 6.5/6.7/7.0

List pause parameters of all NICs

#esxcli network nic pauseParams list
Set pause parameters for a NIC

#esxcli network nic pauseParams set

Cmd options:
-a|--auto=<bool> Enable/disable auto negotiation.
-n|--nic-name=<str> Name of NIC whose pause parameters should be set. (required)
-r|--rx=<bool> Enable/disable pause RX flow control.
-t|--tx=<bool> Enable/disable pause TX flow control.

Append the same commands used above to the rc.local or local.sh file to make the settings persistent across reboots. The file name and location varies depending on the version of ESXi/ESX you are running. For more information on identifying and modifying this file, see Modifying the rc.local or sh.local file in ESX/ESXi to execute commands while booting (2043564).

Note: A best practice is to check the current value of a parameter setting before and after making any change. Some network drivers provide module options which configure flow control functionality within the driver. Module options take effect during startup and, therefore, a reboot of the ESX/ESXi host is required. For more information on how to determine the available module options and to set a option, see Configuring advanced driver module parameters in ESX/ESXi (1017588).

Additional Information

Note: Not all network drivers and NICs allow flow control to be modified or used. For example, the e1000e driver does not support flow control. Use this command to view the parameters for a particular driver:

esxcli system module parameters list --module driver_name

You can filter the results with a grep command to get the value of a specific parameter:

esxcli system module parameters list --module e1000 | grep "FlowControl" .

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Unable to connect to an ESX host using Secure Shell (SSH)
Configuring advanced driver module parameters in ESX/ESXi
Using Tech Support Mode in ESXi 4.1, ESXi 5.x, and ESXi 6.x
Modifying the rc.local or local.sh file in ESX/ESXi to execute commands while booting
在 VMware ESXi 和 VMware ESX 上配置流控制
VMware ESXi および VMware ESX 上のフロー制御を構成する

Impact/Risks:
By default, flow control is enabled on all network interfaces in VMware ESXi and ESX. This is the preferred configuration in 1GB networks. If there are large numbers of pause frames in an environment, it is usually indicative of an underlying issue that should be investigated.