Realtek NetAdapterCx USB Driver Conflict with Norton (Forced NDIS Fallback Required) - bandwidth download cut in half

Norton 360 for Windows
1

Subject: Realtek NetAdapterCx USB Driver Conflict with Norton (Forced NDIS Fallback Required) - bandwidth download cut in half

Description: I am experiencing a reproducible driver and network stability conflict between Norton and modern Realtek NetAdapterCx USB drivers.

When using the newer NetAdapterCx driver architecture, the system encounters severe download bandwidth drop. The only reliable workaround is to completely uninstall the NetAdapterCx driver package and manually force a fallback to the older legacy NDIS driver framework or removing Norton completely.

When removing Norton completely or using NDIS driver architecture, download bandwidth is fully restored.

There are two topics about this issue but neither is resolved. Writing to see if someone at QA or the engineering department at Norton can start working on this. It’s been more than a year with the issue, maybe more. If Realtek stops issuing the NDIS driver in the future, the only option will be to stop using Norton completely.

image below: with NetAdapterCx driver architecture.

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image below: with NDIS driver architecture

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System Details:

  • OS: Windows 11

  • Architecture: AMD x64

  • Security Software: Norton 360 (Latest Version)

  • Norton: No improvement when disabling all antivirus and firewall settings. VPN is off.

  • Network Controller: Realtek USB GBE Family Controller

  • Problematic Driver Architecture with Norton installed: Realtek USB NetAdapterCx (v11.x)

  • Working Workaround Driver: Realtek USB Legacy NDIS Driver (v10.x)

Steps to Reproduce:

  1. Have Norton 360 installed.

  2. Update to the latest USB Realtek NetAdapterCx network adapter driver.

  3. Observe the network’s download bandwidth cut in half related to Norton’s interaction with the NetAdapterCx polling/I/O model.

  4. Roll back to the legacy NDIS driver version, which immediately resolves the issue, restoring full bandwidth. Uninstalling Norton completely also resolved the issue.

Request: Could the engineering or QA team investigate how Norton’s network stack interacts with the NetAdapterCx driver framework? Users with modern Realtek USB adapters are forced to stay on legacy NDIS drivers or remove Norton completely to keep their connection stable.

2

Have you contacted the Realtek Support about this?

I’ll escalate this thread to get the attention of the appropriate department.

3

@sofwrdude What is the OEM for your computer? Is this older hardware running Windows 11? What is the specific adapter being used, IE: RTL8152B as an example? Does your device show as supported at the link below? Have you considered using the OEM driver package?

SA

4

I updated my RTL8125 PCI-E to the NetAdapterCx Driver and it seems fine - maybe something with Norton and the USB adapter or the speed test server you’re connected to - I notice that my speeds vary drastically even without Norton and before and after switching the driver.

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5

Hi @SoulAsylum,

The internal LAN PCIe 1Gb Realtek RTL8168H is not affected.

Only USB devices. RT8157x64, Realtek USB 5GbE Family Controller and another one tested is the Realtek RTL8156B Gaming USB 2.5GbE Family Controller. They are supported using the link provided and drivers in that link are the ones in use.

If you uninstall Norton, all issues/problems disappear and Realtek cards work flawlessly.

6

Hi @Geek007,

The bandwidth in your two tests is similar in download. Your system doesn’t seem to be affected although your upload seems to vary in that test.

My speeds are constant always. That’s why I am sure there is an issue here. I have a good service provider. Maybe 5 or 50Mb of difference is ok in tests but losing 380Mb is a bug to fix. Also, tests are done without any other device using the bandwidth to be fair.

Seems to be Norton the application that causes the issue when installed. Maybe an issue between Norton and Realtek. Maybe with Laptops only. That’s why more testing is needed, but there is definitely a bug here.

7

Thanks @peterweb,

Just sent them an email today with all the details of the scenario. I hope they answer.

8

Yeah probably with the way Norton is interpreting the USB adapter and NetAdapterCX driver, both my screenshots were taken after the driver update but on different speedtest.net servers.