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Troubleshooting Network Performance Issues With the SonicWall SMA 500v on ESXi

Joe Gehrke

Mar 12 2024

2 min read

The SonicWall Secure Mobile Access (SMA) appliance is an SSLVPN gateway device that allows remote workers to securely access resources on the corporate network. One advantage of using the SMA over the built-in SSLVPN service is the SMA’s ability to provide granular access controls.

One issue we came across recently involved users experiencing slow data transfer speeds when connected to a Remote Desktop Server via the SSLVPN service on a virtual (VMware) SMA appliance. After some investigation, we confirmed that 2-4% of traffic was being dropped, and we sporadically would see latency of over 300 milliseconds on the SMA traffic. Both of these findings pointed to a problem that made the end-user experience unbearable.

Troubleshooting Network Performance with SonicWall SMA

During our investigation, we found a knowledge base article from SonicWall that recommended changing the VMware virtual adapter assigned to the SMA from “Flexible” to “VMXNET3” to address performance/speed. According to VMware, a “Flexible” network adapter can function as either a Vlance or VMXNET adapter, depending on if the VMXNET driver is installed. Both adapter types are older architecture designs. VMWare recommends “VMXNET3” for best performance. However, it will require the virtual machine hardware to be on version 7 or later and VMware tools to be installed on the VMware guest.

To complete the task in the knowledge base article, we performed the following actions:

Log directly into the ESXi host that has the SMA virtual machine on it. Changing the network adapter type is not possible from within vCenter.
Shut down the SMA.
Edit the Setting.
- Go to the VM Options tab.
  - Under General Options, change Guest OS Version to “Other 2.6.x Linux (32-Bit).”
- Go to the Virtual Hardware tab.
  - Expand the network adapter and change the current adapter type to VMXNET3.
- Start the SMA.

After making these changes, our testing showed the dropped packets and latency issues disappeared. More importantly, the client had no issues accessing the Remote Desktop Server environment with the expected degree of performance.

If you need help troubleshooting network performance issues or configuring a SonicWall SMA appliance, please contact us at any time.

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About the Author

Joe Gehrke

Joe has over 13 years of experience working in the IT industry. He started my career in a small computer repair shop and continued to evolve his skills to take on new responsibilities as a Help Desk Administrator, Systems Administrator, and at his current role as a Senior Network Consultant in Sikich’s Network Operation’s Center. He has certifications from VMware, Microsoft, and SonicWall.