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Windows network duplication

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Windows network duplication is a Windows chaos fault that duplicates NETWORK_PACKET_DUPLICATION_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.

Use this fault to test how a workload on a Windows VM behaves when packets are duplicated: whether TCP de-duplication handles the load, whether UDP receivers handle duplicate packets at the application layer, whether monitoring detects bandwidth spikes, and whether on-call alerts fire correctly.

Run your first experiment

If you have not configured the chaos infrastructure yet, go to Quickstart to install the chaos infrastructure and run an experiment end to end.

Use cases​

  • Duplicate packets on the wire: Does TCP de-duplicate correctly, or does the workload's TCP stack misbehave?
  • UDP idempotency: Do UDP receivers handle duplicates correctly, or does the workload process the same event twice?
  • Bandwidth spike: Does the bandwidth spike trigger alerts and/or violate rate limits?

Prerequisites​

  • Windows chaos infrastructure: Install the chaos agent on the target VM. Go to Windows requirements and security considerations.
  • Administrator privileges: Network duplication is an Advanced fault and requires the agent to run as administrator.

Supported environments​

PlatformSupport status
Windows Server VMs with the Windows chaos agent installedSupported
Linux VMsNot supported (use Linux network duplication)

Permissions required​

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

Fault tunables​

Chaos parameters

TunableDescriptionDefault
DURATIONTotal duration of the fault as a Go duration string (for example 30s).30s
NETWORK_PACKET_DUPLICATION_PERCENTAGEPercentage of egress packets to duplicate (0-100).100
DESTINATION_HOSTSComma-separated destination hostnames.""
DESTINATION_IPSComma-separated destination IPs/CIDRs.""
DESTINATION_PORTSComma-separated destination ports.""
NETWORK_PROTOCOLSComma-separated protocols (tcp, udp, icmp).""
NETWORK_WHITELIST_DESTINATION_HOSTSHostnames excluded from duplication.""
NETWORK_WHITELIST_DESTINATION_IPSIPs/CIDRs excluded from duplication.""
NETWORK_WHITELIST_DESTINATION_PORTSPorts excluded from duplication.""
RAMP_TIMEWait period in seconds before and after the fault.0

Tunables that apply to every fault are documented in common tunables for all faults.

Fault execution in brief​

The Windows chaos agent on the target VM installs a network filter that duplicates NETWORK_PACKET_DUPLICATION_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 configurable share of egress packets are sent twice.
  • TCP receivers de-duplicate; UDP receivers see duplicates.
  • Egress bandwidth approximately doubles for affected flows.
  • After the duration ends, the filter is removed and traffic returns to baseline.
When the fault ends

The chaos agent removes the network filter. Egress bandwidth returns to baseline within seconds.

Signals to watch​

Verify the fault execution effect​

  1. Inspect egress bytes on the VM during the chaos window.

    Get-Counter '\Network Interface(*)\Bytes Sent/sec' -Continuous

    Bytes sent per second should rise during the window.

Recovery and cleanup​

  • 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​

  • Egress only: The rule affects egress packets only.
  • TCP often masks duplication: TCP receivers de-duplicate, so the visible effect is bandwidth doubling, not duplicate processing at the app layer.
  • Administrator required: This is an Advanced fault and requires the agent to run as administrator.

Troubleshooting​

Windows network duplication has no observable effect in Harness Chaos Engineering

TCP de-duplicates transparently, so the most visible signal is egress-bandwidth doubling. For UDP workloads, the workload must check for duplicate messages itself.