Getting Started with NetEmul — A Step-by-Step GuideNetEmul is an open-source network emulation framework designed to help network engineers, QA teams, and developers recreate realistic network conditions in a controlled lab environment. Whether you’re validating application behavior under packet loss, testing software upgrades across unreliable links, or building reproducible testbeds for CI/CD, NetEmul simplifies the process of creating, running, and analyzing emulated networks.
What NetEmul Does (High-level)
NetEmul lets you define virtual network topologies and apply configurable impairments such as latency, jitter, packet loss, bandwidth limits, reordering, and duplication. It typically runs on commodity Linux hosts using kernel features (like traffic control — tc) or container-based networking to emulate per-link behavior. NetEmul focuses on reproducibility, automation, and integration with test suites and monitoring tools.
Who Should Use NetEmul
- Network engineers validating routing protocols, BGP/OSPF changes, or VPN behavior.
- QA and SRE teams testing service resilience under degraded network conditions.
- Developers wanting to reproduce field issues locally.
- Academics and students learning about network effects on distributed systems.
Key Concepts and Terminology
- Node — A virtual or physical host participating in the emulated topology.
- Link — A connection between two nodes with configurable characteristics.
- Impairment — Any network condition applied to a link (latency, loss, etc.).
- Scenario — A saved configuration that details nodes, links, and impairments for a test.
- Controller — The NetEmul service/CLI that deploys scenarios to hosts or container clusters.
System Requirements
- Linux (recommended: Ubuntu 20.04 or later) with root access for traffic control configuration.
- Docker (optional) for container-based node isolation.
- tc (iproute2) and netem kernel modules available.
- Python 3.8+ for the NetEmul CLI and scripts (if NetEmul’s tooling is Python-based).
- Sufficient CPU/RAM to run the number of nodes and traffic load you plan to emulate.
Installation
- Install kernel tools and dependencies:
- iproute2 (contains tc), tc-netem support in kernel.
- Install Docker if using containerized nodes.
- Install NetEmul:
- If NetEmul provides packages: use apt/pip/docker image per project docs.
- Or clone the repository and install dependencies:
git clone https://example.com/netemul.git cd netemul pip install -r requirements.txt python setup.py install
- Verify installation:
- Run
netemul --versionandtc qdisc showto ensure netem kernel modules load.
- Run
Quickstart: Create Your First Scenario
- Define topology. Example: three nodes (client, router, server) with two links.
- Configure link impairments: e.g., client→router 50ms latency, 0.5% loss; router→server 20ms latency, 0% loss.
- Deploy scenario to local host or docker-compose environment.
- Run traffic tests (iperf3, curl, or custom test harness).
- Collect logs and metrics, then adjust impairments as needed.
Example scenario (YAML-like pseudocode):
nodes: - name: client image: alpine - name: router image: ubuntu - name: server image: nginx links: - endpoints: [client, router] latency: 50ms loss: 0.5% - endpoints: [router, server] latency: 20ms loss: 0% Running Traffic Tests
- Use iperf3 for TCP/UDP throughput measurement:
- Start server:
iperf3 -s - Run client:
iperf3 -c <server-ip> -t 30
- Start server:
- Use h2load or wrk for HTTP/2 and HTTP/1.1 load testing.
- Use tcptraceroute, ping, and curl for basic connectivity and latency checks.
Automation and CI Integration
- Store scenarios as YAML/JSON in your repo.
- Add a pipeline step that spins up NetEmul, runs tests, and tears down the environment.
- Use artifact storage for logs, pcap files, and test reports.
Sample CI step (pseudo):
- run: netemul apply scenario.yaml - run: pytest tests/ --junitxml=results.xml - run: netemul destroy Monitoring and Debugging
- Capture pcaps with tcpdump on emulated links.
- Use Prometheus/Grafana exporters to collect metrics from services.
- Inspect tc qdisc with
tc -s qdiscto verify impairments. - Use container logs and NetEmul controller logs for error details.
Advanced Topics
- Per-flow impairments using iptables or tc filters.
- Emulating asymmetric links and competing traffic patterns.
- Integrating with network simulators (ns-3) for hybrid experiments.
- Scaling to multiple hosts with distributed controllers.
Best Practices
- Start with simple scenarios and gradually increase complexity.
- Version-control scenario definitions.
- Keep tests deterministic: seed random loss patterns when needed.
- Limit scope per test to reduce noise and improve diagnosability.
Troubleshooting Checklist
- Are netem modules loaded?
lsmod | grep netem - Is tc installed and functional?
tc qdisc show - Are container network namespaces correctly configured?
ip netns - Did you capture pcaps to confirm impairments?
tcpdump -i any -w capture.pcap
Resources and Further Reading
- Linux tc and netem documentation.
- iperf3, tcpdump, and common load-testing tools.
- NetEmul repository and examples (follow project README and wiki).
NetEmul provides a powerful way to reproduce real-world network conditions in the lab. Start small, automate scenarios, and use captures and metrics to iterate toward reliable, reproducible tests.
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