Network Utilities

Diagnose and monitor connections

Network debugging shouldn't require a degree in networking. These utilities make it straightforward.

Port Investigation

port — What's Using a Port?

Find what's listening on a specific port:

port 3000
# ▸ PID: 12345
# ▸ Process: node
# ▸ User: bliss
# ▸ Command: node server.js

Cross-platform (uses lsof, ss, or netstat depending on availability).

The first command to run when "port already in use" errors appear.

ports — All Listening Ports

See everything listening:

ports
# ━━━ Listening Ports ━━━
# PORT    PID     PROCESS     USER
# 22      1234    sshd        root
# 3000    5678    node        bliss
# 5432    9012    postgres    postgres
# 8080    3456    nginx       www-data

Quick overview of all services accepting connections.

Connectivity Testing

netcheck — Full Connectivity Test

Comprehensive network diagnostics:

netcheck
# ━━━ Network Check ━━━
# ✓ DNS Resolution: OK (1.1.1.1)
# ✓ Gateway: OK (192.168.1.1)
# ✓ Internet: OK (google.com)

Three-stage test:

1. DNS resolution (can we resolve domain names?)
2. Gateway reachability (can we reach our router?)
3. Internet connectivity (can we reach the internet?)

Run this first when debugging network issues. Pinpoints where the problem is.

Interface Information

netif — Active Interfaces

Network interface details:

netif
# ━━━ Network Interfaces ━━━
# ▸ en0 (WiFi)
#   └─ IP: 192.168.1.100
#   └─ MAC: aa:bb:cc:dd:ee:ff
# ▸ lo0 (Loopback)
#   └─ IP: 127.0.0.1

Quick way to find your local IP address.

wifi — WiFi Details (macOS)

WiFi status and signal strength:

wifi
# ━━━ WiFi ━━━
# ▸ SSID: MyNetwork
# ▸ BSSID: 00:11:22:33:44:55
# ▸ Channel: 36
# ▸ Signal: -45 dBm
# [████████████████░░░░] 80%

Visual signal strength bar. macOS only.

Signal quality:

• -30 dBm: Excellent (100%)
• -50 dBm: Good (75%)
• -70 dBm: Fair (50%)
• -80 dBm: Poor (25%)

Connection Monitoring

connections — Active Connections

See all network connections:

connections        # All protocols
connections tcp    # TCP only
connections udp    # UDP only

Shows:

• Protocol (TCP/UDP)
• Local address and port
• Remote address and port
• Connection state (ESTABLISHED, LISTEN, etc.)

Useful for seeing what your machine is talking to.

Bandwidth Monitoring

bandwidth — Live Bandwidth Usage

Real-time network usage:

bandwidth
# Opens: nload, iftop, or nethogs (whichever is available)

Priority order:

1. nload — Simple bandwidth graph (recommended)
2. iftop — Connection-based view
3. nethogs — Process-based view

Install one for live monitoring:

# macOS
brew install nload

# Linux
sudo apt install nload
# or: sudo pacman -S nload

Quick Aliases

Alias	Command	Description
lsof-net	lsof -i -P -n	All network file descriptors
netstat-listen	netstat -tlnp	Listening sockets (Linux)
ss-listen	ss -tlnp	Listening sockets (modern)

ss is faster than netstat. Use it on modern Linux systems.

Workflows

"Port Already in Use" Error

# Find what's using the port
port 8080

# Kill it if it's stale
kill <PID>

# Or find and kill in one go
pk node  # Kill all node processes

Debug Network Issues

# Start with connectivity check
netcheck

# If DNS fails: flush DNS cache
flushdns  # macOS

# If gateway fails: check interface
netif

# If internet fails but gateway works: ISP issue

# Check signal strength (WiFi)
wifi

Find Your Local IP

# Quick method
netif

# Or specific interface
ifconfig en0 | grep inet
# or: ip addr show wlan0  # Linux

Monitor Suspicious Activity

# See all connections
connections

# Find specific remote host
connections | grep 93.184.216.34

# Live bandwidth monitoring
bandwidth

Debug Slow Network

# Check if it's WiFi signal
wifi

# Monitor bandwidth usage
bandwidth

# Check what's using network
nethogs  # Shows per-process usage

Pro Tips

Use port first: 90% of port issues are solved by finding and killing the process using it.

Trust netcheck: It pinpoints the problem layer. DNS vs gateway vs internet issues need different solutions.

Monitor bandwidth: If things are slow, run bandwidth. Often reveals a background process hogging the connection.

WiFi signal matters: Below -70 dBm and you'll have issues. Move closer to the router or use ethernet.

ss over netstat: On modern Linux, ss is faster and has better filtering options.

Kill stale processes: If port 3000 shows a process but you're not running anything, kill it. Probably a zombie from a crashed dev server.

Know your local IP: Use netif to quickly grab it for SSH or local testing.

Use proper tools: Install nload or iftop for serious network monitoring. The scripts are for quick checks.