Linux Networking Commands Cheat Sheet — 40 Commands You Actually Use

Diagnostics

These are the commands you reach for when something is broken.

# Check if a host is reachable
ping -c 4 example.com

# Trace route
traceroute example.com
mtr example.com          # interactive version

# DNS lookup
dig example.com
dig +short example.com A
dig @8.8.8.8 example.com  # specific DNS server

# Reverse DNS
dig -x 93.184.216.34

# What's listening on ports
ss -tlnp
netstat -tlnp   # older systems

# Which process owns a port
lsof -i :8080
fuser 8080/tcp

Interface Management

# Show all interfaces
ip addr show
ip a

# Show routing table
ip route show

# Add IP address
ip addr add 192.168.1.100/24 dev eth0

# Bring interface up/down
ip link set eth0 up
ip link set eth0 down

# Show ARP table
ip neigh show

# Flush DNS cache (systemd)
resolvectl flush-caches

Traffic Analysis

# Capture packets
tcpdump -i eth0
tcpdump -i eth0 port 80        # HTTP only
tcpdump -i eth0 -w capture.pcap # save to file

# Bandwidth per interface
nload
iftop
vnstat

# Bandwidth per process
nethogs

# Speed test between hosts
iperf3 -c speedtest.example.com

Curl Essentials

# GET with headers
curl -v https://example.com

# POST JSON
curl -X POST https://api.example.com/data \
  -H 'Content-Type: application/json' \
  -d '{"key": "value"}'

# Follow redirects
curl -L https://example.com

# Download file
curl -O https://example.com/file.tar.gz

# Resume broken download
curl -C - -O https://example.com/large-file.iso

# Headers only
curl -I https://example.com

SSH Tunnels

# Local port forward
ssh -L 5432:localhost:5432 user@server

# Remote port forward
ssh -R 3000:localhost:3000 user@server

# SOCKS proxy
ssh -D 1080 user@server

# Background tunnel
ssh -fN -L 5432:localhost:5432 user@server

Firewall Quick Ref

# List rules
iptables -L -n -v

# Allow SSH
iptables -A INPUT -p tcp --dport 22 -j ACCEPT

# Block an IP
iptables -A INPUT -s 10.0.0.5 -j DROP

# nftables
nft list ruleset
nft add rule inet filter input tcp dport 22 accept

Bookmark this. You'll need it at 3 AM when DNS breaks again.