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This guide explains how to diagnose and remediate network performance issues in Azure. It covers recommended tools, how to run end-to-end tests with the Azure Connectivity Toolkit (AzCTK), how to interpret results, and practical checks to narrow down root causes. Use these Azure-native and community tools for monitoring and diagnosing connectivity, throughput, and latency issues: AzCTK is particularly useful for automated, repeatable tests of TCP connectivity, packet loss, latency, and multi-session bandwidth.

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AzCTK overview and common cmdlets

AzCTK provides cmdlets that replicate real-world TCP behavior across different session counts and window sizes. Useful cmdlets include: Key AzCTK features:
  • End-to-end packet loss and latency tests.
  • Single-thread and multi-thread bandwidth tests (multiple concurrent sessions).
  • Ability to vary TCP window sizes to emulate different client behaviors.
  • Installable as a PowerShell module for automation and scripting.
The image describes AzCTK features, including end-to-end packet loss and latency tests, simulating single/multi-thread bandwidth tests, and an installable PowerShell module for ease of use.
The screenshot above shows a sample multi-stage test output with bandwidth, packet loss, and latency reported for different session counts and stages. Reviewing these metrics across stages helps identify capacity constraints, device misconfigurations, or endpoint limitations.

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Example: running a Get-LinkPerformance test

Run a basic multi-stage performance test:
This triggers a series of TCP tests (no-load ping, single-session, multi-session, varying window sizes) over the specified duration. Example (trimmed) output:

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Interpreting the core metrics

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Troubleshooting checklist

When results show elevated loss, reduced bandwidth, or increased latency, validate configuration and capacity across all layers:
  • Azure networking:
    • NSGs and UDRs for unintended rules.
    • Load Balancer configuration and health probes.
    • VM size and NIC capabilities (maximum bandwidth, Accelerated Networking).
  • On-premises network:
    • Routers, switches, firewalls for queueing or drops.
    • MTU settings and VLAN configurations.
  • Connectivity circuits:
    • ExpressRoute or VPN circuit health and advertised BGP routes.
  • Endpoints:
    • Server NIC drivers, OS TCP stack tuning, CPU/memory saturation.
Run tests from both endpoints (on-premises → Azure and Azure → on-premises). Vary session counts and TCP window sizes to isolate whether the bottleneck is in the network or on the endpoints.

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Installation and quick start

Install AzCTK from the PowerShell Gallery and import it into your session:
Run PowerShell as an administrator if you need to install modules system-wide. Ensure you have a supported PowerShell version (PowerShell 5.1 or PowerShell Core) and an execution policy that permits module installation.

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Example troubleshooting workflow

  1. Baseline test: run Get-LinkPerformance with default stages to capture baseline bandwidth/latency/loss.
  2. Reproduce: run the same tests from the opposite endpoint to confirm symmetry.
  3. Isolate: increase session counts and vary window sizes to determine whether the limitation changes (network vs. endpoint).
  4. Inspect: review NSGs, UDRs, load balancers, VM SKUs, and NIC settings. Check on-premises devices and circuit state.
  5. Remediate: adjust configuration (e.g., increase VM size, tune TCP, resolve MTU mismatches), then retest.
Using AzCTK within a structured troubleshooting process helps pinpoint whether network performance issues are caused by capacity limits, misconfiguration, or endpoint constraints — enabling targeted, effective remediation.

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