> For the complete documentation index, see [llms.txt](https://developer.harness.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developer.harness.io/resilience-testing/chaos-engineering/faults/chaos-fault-categories/windows/windows-network-loss.md).

# Windows network loss

Windows network loss is a Windows chaos fault that drops `NETWORK_PACKET_LOSS_PERCENTAGE` percent of egress packets from the target Windows VM to destinations listed in `DESTINATION_HOSTS`/`DESTINATION_IPS` on ports `DESTINATION_PORTS` and protocols `NETWORK_PROTOCOLS` for `DURATION`, then removes the filter. The fault runs through the Windows chaos agent installed as a service on the target VM. Use the `NETWORK_WHITELIST_*` tunables to spare specific destinations from the loss.

Use this fault to test how a workload on a Windows VM behaves when packet loss spikes: whether TCP retransmits stay within the SLA, whether application-layer retries recover correctly, and whether monitoring detects the regression within the alerting SLA.

{% hint style="info" %}
**RUN YOUR FIRST EXPERIMENT**

If you have not configured the chaos infrastructure yet, go to [Quickstart](/resilience-testing/chaos-engineering/new-to-chaos-engineering/quickstart.md) to install the chaos infrastructure and run an experiment end to end.
{% endhint %}

***

### Use cases <a href="#use-cases" id="use-cases"></a>

* **Lossy network:** When packet loss spikes, do TCP retransmits and application retries recover the request inside the SLA?
* **Cluster membership:** Does Windows Failover Cluster stay healthy when heartbeats lose a percentage of packets?
* **Real-time workloads:** Does media or voice quality degrade gracefully under loss?

***

### Prerequisites <a href="#prerequisites" id="prerequisites"></a>

* **Windows chaos infrastructure:** Install the chaos agent on the target VM. Go to [Windows requirements and security considerations](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/windows/windows-chaos-permissions.md).
* **Administrator privileges:** Network loss is an Advanced fault and requires the agent to run as administrator.

***

### Supported environments <a href="#supported-environments" id="supported-environments"></a>

| Platform                                                  | Support status                                                                                                                                     |
| --------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------- |
| Windows Server VMs with the Windows chaos agent installed | Supported                                                                                                                                          |
| Linux VMs                                                 | Not supported (use [VMware network loss](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/vmware/linux/vmware-network-loss.md)) |

***

### Permissions required <a href="#permissions-required" id="permissions-required"></a>

This fault is classified as **Advanced** and requires the chaos agent to run as administrator on the target VM.

***

### Fault tunables <a href="#fault-tunables" id="fault-tunables"></a>

**Chaos parameters**

| Tunable                               | Description                                                              | Default |
| ------------------------------------- | ------------------------------------------------------------------------ | ------- |
| `DURATION`                            | Total duration of the fault as a Go duration string (for example `30s`). | `30s`   |
| `NETWORK_PACKET_LOSS_PERCENTAGE`      | Percentage of egress packets to drop (0-100).                            | `100`   |
| `DESTINATION_HOSTS`                   | Comma-separated destination hostnames.                                   | `""`    |
| `DESTINATION_IPS`                     | Comma-separated destination IPs/CIDRs.                                   | `""`    |
| `DESTINATION_PORTS`                   | Comma-separated destination ports.                                       | `""`    |
| `NETWORK_PROTOCOLS`                   | Comma-separated protocols (`tcp`, `udp`, `icmp`).                        | `""`    |
| `NETWORK_WHITELIST_DESTINATION_HOSTS` | Hostnames excluded from loss.                                            | `""`    |
| `NETWORK_WHITELIST_DESTINATION_IPS`   | IPs/CIDRs excluded from loss.                                            | `""`    |
| `NETWORK_WHITELIST_DESTINATION_PORTS` | Ports excluded from loss.                                                | `""`    |
| `RAMP_TIME`                           | Wait period in seconds before and after the fault.                       | `0`     |

Tunables that apply to every fault are documented in [common tunables for all faults](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/common-tunables-for-all-faults.md).

***

### Fault execution in brief <a href="#fault-execution-in-brief" id="fault-execution-in-brief"></a>

The Windows chaos agent on the target VM installs a network filter that drops `NETWORK_PACKET_LOSS_PERCENTAGE` percent of egress packets matching the destination/port/protocol filters (minus the whitelist) for `DURATION`, then removes the filter.

***

### Expected behavior during fault execution <a href="#expected-behavior-during-fault-execution" id="expected-behavior-during-fault-execution"></a>

* A configurable share of egress packets are dropped.
* TCP retransmits rise; throughput drops.
* Application-layer error rates may rise; retry budgets may be consumed.
* After the duration ends, the filter is removed and packet loss returns to baseline.

{% hint style="info" %}
**WHEN THE FAULT ENDS**

The chaos agent removes the network filter. Packet loss returns to baseline within seconds.
{% endhint %}

#### Signals to watch <a href="#signals-to-watch" id="signals-to-watch"></a>

* **Connectivity:** Use a [command probe](/resilience-testing/chaos-testing/probes/command-probe.md) running `Test-NetConnection <host> -InformationLevel Detailed`.
* **Workload:** Use an [HTTP probe](/resilience-testing/chaos-engineering/use-chaos-engineering/probes/http-probe.md) and assert error budget is respected.

***

### Verify the fault execution effect <a href="#verify-the-fault-execution-effect" id="verify-the-fault-execution-effect"></a>

1. **Ping a target host from the VM during the chaos window.**

   ```powershell
   ping <DESTINATION_HOSTS_entry> -n 100
   ```

   Loss percentage should match `NETWORK_PACKET_LOSS_PERCENTAGE`.
2. **Run a quick HTTP call from a peer machine.**

   Error rate should reflect the loss.

***

### Recovery and cleanup <a href="#recovery-and-cleanup" id="recovery-and-cleanup"></a>

* **End of duration:** The chaos agent removes the filter.
* **Abort:** Stopping the experiment also removes the filter.
* **Manual recovery:** Restart the chaos agent service if filters survive.

***

### Limitations <a href="#limitations" id="limitations"></a>

* **Egress only:** The rule affects egress packets only.
* **Administrator required:** This is an Advanced fault and requires the agent to run as administrator.

***

### Troubleshooting <a href="#troubleshooting" id="troubleshooting"></a>

<details>

<summary>Windows network loss has no observable effect in Harness Chaos Engineering</summary>

Verify DESTINATION\_HOSTS or DESTINATION\_IPS match the traffic you are measuring. Confirm the agent is running as administrator. If the workload uses a proxy or VPN, the rule may not match the real egress path.

</details>

<details>

<summary>Windows network loss fails with access denied</summary>

The chaos agent must run as administrator to install network filters. Reinstall the agent as administrator and retry.

</details>

***

### Related faults <a href="#related-faults" id="related-faults"></a>

* [Windows network latency](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/windows/windows-network-latency.md): Add latency instead of dropping packets.
* [Windows blackhole chaos](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/windows/windows-blackhole-chaos.md): Block traffic entirely instead of dropping a percentage.