clab-softnet — Simple 2-Node ContainerLab Topology

Purpose: Minimal containerlab topology with dual-stack IPv4/IPv6 support

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Goal

A simple 2-node containerlab topology:

• Two Ubuntu nodes (node1, node2) connected by a single p2p link on eth1
• IPv4: 10.0.0.0/24
• IPv6: fc00::/64

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Repository Structure

clab-softnet/
├── containerlab/
│   ├── basic-lab.clab.yml      # 2-node topology (node1 <-> node2)
│   ├── Dockerfile              # Ubuntu 24.04 image (sleep infinity as PID 1)
│   ├── bin/
│   │   └── entrypoint.sh       # Network configuration script (called via exec)
│   ├── configs/                # Per-node configuration
│   │   ├── node1.cfg
│   │   └── node2.cfg
│   ├── deploy.sh               # Deploy helper
│   └── destroy.sh              # Destroy helper
├── scripts/
│   └── build-image.sh          # Build custom Docker image
├── PLAN.md                     # Architecture and design notes
├── README.md                   # This file
└── TROUBLESHOOTING.md          # Debug guide

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Prerequisites

• containerlab
• docker
• Linux

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Quick Start

1. Build Docker Image

cd containerlab
docker build -t clab-ubuntu-softnet:latest .

Or use the helper script:

./scripts/build-image.sh

2. Deploy Topology

cd containerlab
containerlab deploy -t basic-lab.clab.yml

Containerlab will:

1. Start both containers (sleep infinity as PID 1)
2. Create the node1:eth1 <-> node2:eth1 veth link
3. Run bash /entrypoint.sh inside each container via exec

The entrypoint output is shown directly in the deploy log.

3. Verify Connectivity

# Check node status
containerlab inspect -t basic-lab.clab.yml

# IPv4 ping
docker exec clab-basic-lab-node1 ping -c 3 10.0.0.2

# IPv6 ping
docker exec clab-basic-lab-node1 ping -6 -c 3 fc00::2

4. Destroy Topology

cd containerlab
containerlab destroy -t basic-lab.clab.yml --cleanup

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Configuration

IP Addressing

Node	eth1 IPv4	eth1 IPv6	Peer IPv4	Peer IPv6
node1	10.0.0.1/24	fc00::1/64	10.0.0.2	fc00::2
node2	10.0.0.2/24	fc00::2/64	10.0.0.1	fc00::1

Each config file (configs/node1.cfg, configs/node2.cfg) defines all six values: NODE_IP, NODE_PREFIX, NODE_IP6, NODE_PREFIX6, PEER_IP, PEER_IP6

Network Topology

    +----------+       +----------+
    |  node1   | eth1  |  node2   |
    |10.0.0.1  |-------|10.0.0.2  |
    |fc00::1   |       |fc00::2   |
    +----------+       +----------+

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How exec Works

The topology uses containerlab's exec to run the entrypoint after links are created:

nodes:
  node1:
    binds:
      - configs/node1.cfg:/etc/nodes/node1.cfg:ro
    exec:
      - bash /entrypoint.sh

This guarantees eth1 already exists when the script runs — no polling loop needed. The container stays alive via CMD ["sleep", "infinity"] in the Dockerfile.

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Commands Reference

# Deploy
containerlab deploy -t basic-lab.clab.yml

# Inspect
containerlab inspect -t basic-lab.clab.yml

# Shell access
docker exec -it clab-basic-lab-node1 bash
docker exec -it clab-basic-lab-node2 bash

# Destroy
containerlab destroy -t basic-lab.clab.yml --cleanup

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Troubleshooting

See TROUBLESHOOTING.md.

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License

GNU General Public License v3.0