Windows 11 HLK NDISTest6.5: Multiple 2-Machine tests failing with breakpoint hits and packet loss across different NICs

The provided context does not document any known NDISTest 6.5 issues that are specific to Windows 11 25H2 or HLK 10.1.26100.8328, nor does it list a different recommended HLK version for that OS. However, it does contain guidance that can help narrow down the cause of the failures you see across different NICs.

For the NDISTest 6.5 two‑machine tests, the documentation emphasizes that many failures are caused by topology, device selection, or connectivity issues rather than by the specific NIC or driver:

1. For any two‑machine LAN test failures, the first recommended step is to run the “NDISTest 6.5 – [2 Machine] – CheckConnectivity” job. This job verifies that the test and support devices can communicate correctly by doing a basic send/receive. If this job fails, the logs will show whether the test and support NICs cannot communicate bidirectionally. In that case, the issue is considered a connectivity or configuration problem rather than a specific test defect.
2. The CheckConnectivity job relies on an autodetection script (detect.wsf) to identify the message and support NICs. Autodetection only works when the machines are set up in the recommended topology:
   • Test machine: contains the target NIC and a message NIC.
   • Support machine: contains a support NIC and a message NIC.
   • The support NIC must be directly cabled to the test NIC (no switch or hub in between).
   • The message NICs are the NICs used to reach the HLK controller and the rest of the lab network.
   • Any additional connected Ethernet devices can break autodetection and require manual renaming of NICs to indicate their roles (for example, naming them MessageDevice and SupportDevice0).
3. If the “Run script to detect devices and populate parameters” task in CheckConnectivity fails, the documentation instructs opening detect.wtl to see which device was not detected. Mis‑detected or mis‑assigned NIC roles can lead to packet‑loss‑type failures in multiple NDISTest 6.5 jobs, which matches the pattern of many different tests failing in the same way across different NICs.
4. For general NDISTest 6.5 two‑machine jobs such as TxFlowControl, InterruptModeration, OffloadMisc, OffloadUSO, KeepAlive, and SRIOVTestingFailover, the guidance is to:
   • Ensure the LAN Testing Prerequisites have been followed for cabling, IP configuration, and machine roles.
   • Use the NDISTest HTML logs (for example, checkconnectivity.htm and ndistest.htm under the Client folder) to identify where the failures occur (preconfig, main test, or postconfig) and whether they are due to connectivity, configuration, or protocol‑level issues.
   • Use the generic HLK troubleshooting guidance for any test failures.

Based on the documentation, the most productive next steps for the scenario described are:

1. Run NDISTest 6.5 – [2 Machine] – CheckConnectivity and confirm it passes. If it fails, inspect detect.wtl and checkconnectivity.htm to verify:
   • The correct NICs are selected as test/support/message devices.
   • The test and support NICs are directly connected.
   • There are no extra active Ethernet connections that could confuse autodetection.
2. If autodetection cannot be made to work due to lab topology, rename the NICs explicitly (for example, MessageDevice and SupportDevice0) as described in the CheckConnectivity troubleshooting section so that the scripts can reliably identify them.
3. After CheckConnectivity passes, rerun a subset of the failing NDISTest 6.5 jobs and review the NDISTest HTML logs (ndistest.htm and the per‑test HTML logs) for any remaining breakpoint or packet‑loss errors.

The context does not provide information about specific HLK builds or hotfixes for Windows 11 25H2, nor does it record other users’ reports of the exact breakpoint/packet‑loss pattern described. For version‑specific issues or potential bugs in the HLK tests themselves, the next escalation path would be to open a support case with Microsoft using the HLK logs and configuration details.

References:

• NDISTest 6.5 - [2 Machine] - SRIOVTestingFailover
• Troubleshooting LAN Testing
• The NDISTest 6.5 - [2 Machine] - CheckConnectivity job
• NDISTest 6.5 - [2 Machine] - OffloadUSO
• NDISTest 6.5 - [2 Machine] - OffloadMisc
• NDISTest 6.5 - [2 Machine] - InterruptModeration
• NDISTest 6.5 - [2 Machine] - KeepAlive
• NDISTest 6.5 - [2 Machine] - TxFlowControl