Troubleshooting network performance issues in a vSphere environment

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

Networking performance both to and from the ESXi host and/or virtual machines is not optimal.

Environment

• VMware vCenter Server 7.x
• VMware vCenter Server 8.x
• VMware vCenter Server 9.0.x

Cause

Network problems can have several causes: 

• Resource shares for virtual machine network  are too few
• Network packet size (MTU) is too large, which may result in high network latency
• Network packet size (MTU) is too small, which may increase the demand for CPU resources needed for processing of each packet

Resolution

The following ESXi host components can contribute to network performance:

• Validate that each troubleshooting step below is valid for the environment
• Each step provides instructions or links to a document for validating and taking corrective action as necessary
• Steps are ordered in the correct sequence to isolate the issue and identify the proper resolution
• Please do not skip a step

1. Verify that the latest version of VMware Tools is installed in the virtual machines
   • Verifying a VMware Tools build version and Overview of VMware Tools
   • VMware Tools versions included with VMware ESXi 6.x, 7.x, and 8.x
2. Verify the appropriate network driver for the virtual machine based on environmental needs
   • Choosing a network adapter for your virtual machine
   • VMware vSphere Documentation: Virtual Machine Networking (Search for "Virtual Network Adapters" and/or "NIC Types")
3. VMware recommends using multiple NICs on the associated virtual switch to increase the overall network capacity for portgroups that contain many virtual machines or several virtual machines that are very active on the network. 
   • NIC teaming in ESXi and ESX
   • VMware vSphere Documentation: NIC Teaming and Failover
4. Verify the speed and duplex settings of the installed network adapters
   • Configuring the speed and duplex of an ESX / ESXi host network adapter
5. Verify that the portgroup and virtual switch are not configured for promiscuous mode
   • Configuring promiscuous mode on a virtual switch or portgroup
   • VMware vSphere Documentation: NIC Teaming and Failover
   • vSphere Documentation: Performance Monitoring and Analysis
6. Verify that Jumbo Frames settings are consistent across the VM, vSwitch and the physical switch
7. Verify if the Driver/Firmware versions are compatible according to the VMware Compatibility Guide
   • Check the IOVP (I/O Vendor Program) certified drivers
8. Verify if the packets are being sent/received at the ESXi Host layer
   • Packet capture on ESXi using the pktcap-uw tool