linux-networking

Purpose

This skill handles Linux networking tasks, including IP configuration with Netplan, firewall management via UFW or Nftables, DNS setup, VPN configuration for Wireguard or Tailscale, and inter-instance routing on systems like System76.

When to Use

Use this skill for server setup on Ubuntu/Debian systems, securing applications with firewalls, establishing secure remote access via VPN, resolving DNS issues in containerized environments, or optimizing routing between networked instances in data centers or edge devices.

Key Capabilities

• Configure static/dynamic IP addresses using Netplan YAML files (e.g., set interface to DHCP or static IP).
• Manage firewalls with UFW for simple rules (e.g., allow/deny ports) or Nftables for advanced packet filtering via tables and chains.
• Handle DNS resolution with tools like systemd-resolved or /etc/resolv.conf edits.
• Set up VPNs: Wireguard for peer-to-peer tunnels using wg-quick, or Tailscale for automatic mesh networks with key authentication.
• Implement inter-instance routing on System76 hardware, such as setting up OSPF or static routes for multi-device communication.

Usage Patterns

Always run commands with sudo for root privileges. For scripts, check if services like NetworkManager or systemd-networkd are active. Use environment variables for sensitive data, e.g., export TAILSCALE_API_KEY=$SERVICE_API_KEY before Tailscale operations. In AI responses, structure tasks as sequential commands: first validate config files, then apply changes, and finally verify with diagnostic tools. For automation, wrap commands in bash scripts with error checks, e.g., use set -e to exit on failure.

Common Commands/API

• Netplan configuration: Edit /etc/netplan/01-netcfg.yaml with content like network: version: 2 renderer: networkd ethernets: eno1: dhcp4: true, then run sudo netplan apply.
• UFW firewall: Enable with sudo ufw enable, add rules like sudo ufw allow 22/tcp, and check status with sudo ufw status verbose.
• Nftables firewall: Load rules from /etc/nftables.conf (e.g., table ip filter { chain input { type filter hook input priority 0; policy accept; } }), then apply with sudo nft -f /etc/nftables.conf.
• DNS management: Edit /etc/resolv.conf (e.g., add nameserver 8.8.8.8), or use systemd-resolve --set-dns=8.8.8.8 eth0.
• Wireguard VPN: Generate keys with wg genkey | tee privatekey | wg pubkey > publickey, configure /etc/wireguard/wg0.conf with [Interface] PrivateKey = <key> Address = 10.0.0.1/24, and start with sudo wg-quick up wg0.
• Tailscale VPN: Authenticate with tailscale up --authkey $TAILSCALE_API_KEY, then manage peers via Tailscale API (e.g., GET https://api.tailscale.com/api/v2/devices).
• Inter-instance routing: Add static routes with sudo ip route add 192.168.1.0/24 via 10.0.0.1, or configure OSPF on System76 using quagga with commands like router ospf in vtysh.

Integration Notes

Integrate with orchestration tools like Ansible by using modules such as ansible.builtin.shell for running Netplan commands, or community.general.ufw for firewall rules. For Tailscale, pass API keys via environment variables (e.g., $TAILSCALE_API_KEY) and use their HTTP API for device management. Wireguard integrates with systemd by enabling services via sudo systemctl enable wg-quick@wg0. Ensure compatibility with NetworkManager by disabling it for Netplan (e.g., sudo systemctl stop NetworkManager). For DNS, link with systemd-resolved in containers by mounting /etc/resolv.conf. Always validate configs with tools like nmcli or ip a before applying changes.

Error Handling

Check for permission errors by prefixing commands with sudo; if netplan apply fails with "Invalid YAML", validate the file with yamllint /etc/netplan/01-netcfg.yaml. For UFW/Nftables, use sudo ufw status or sudo nft list ruleset to debug rules; common issues include port conflicts—resolve by checking with ss -tuln. VPN errors: If Wireguard fails to start, verify keys with wg show and check logs with journalctl -u wg-quick@wg0; for Tailscale, handle authentication failures by re-exporting $TAILSCALE_API_KEY and retrying. Routing problems: Use ip route show to diagnose; if routes don't propagate, restart networking with sudo systemctl restart networking. Always log outputs in scripts using >> error.log 2>&1.

Concrete Usage Examples

1. Set up a basic firewall on Ubuntu: First, enable UFW with sudo ufw enable. Then, allow SSH: sudo ufw allow 22. Verify: sudo ufw status. This secures the server while permitting remote access.
2. Configure a Wireguard VPN tunnel: Create a config file at /etc/wireguard/wg0.conf with [Interface] Address = 10.0.0.1/24 PrivateKey = <generated_key>. Start it: sudo wg-quick up wg0. Test connectivity: ping 10.0.0.2. This establishes a secure link between instances.

Graph Relationships

• Related to cluster: linux
• Connected via tags: networking (direct link), linux (cluster parent), firewall (sub-skill), vpn (dependency), tailscale (specific tool)
• Outgoing edges: integrates with linux-security for broader protection, links to linux-storage for network-mounted volumes
• Incoming edges: depends on linux-basics for core OS commands, referenced by devops-tools for automation workflows