🌐 IP Configuration
ip addr show # all interfaces
ip a # short
ip route show # routing table
ip route get 8.8.8.8 # which route
hostname; hostname -I
hostnamectl set-hostname myserver
# /etc/hosts (manual override)
127.0.0.1 localhost
192.168.1.10 myapp.local
🔍 DNS Tools
dig example.com
dig example.com +short
dig @8.8.8.8 example.com # specific resolver
dig example.com MX
dig -x 8.8.8.8 # reverse DNS
# Propagation check
for ns in 8.8.8.8 1.1.1.1 9.9.9.9; do
dig @$ns example.com +short
done
📡 Connection Test
ping -c 4 example.com
traceroute example.com
mtr example.com # live trace 🔥
curl -v https://x.com # full debug
curl -I url # headers only
curl -L url # follow redirect
curl -X POST -d "data" url
curl -H "Authorization: Bearer X" url
curl -o file.zip url
curl -w "%{http_code} %{time_total}\n" -o /dev/null -s url
wget -c url # resume download
🔌 Port & Connection
ss -tulnp # listening 🔥
ss -tunap # all
lsof -i :80
netstat -an | grep :80 | wc -l # active connections
nc -zv example.com 443 # test open
nc -l 8080 # listen for testing
python3 -m http.server 8000 # quick web server
🔬 Packet Capture
sudo tcpdump -i any port 80
sudo tcpdump -i eth0 host example.com -w cap.pcap
sudo tcpdump -r cap.pcap
📊 Bandwidth
sudo iftop # per-connection live
nload eth0 # interface bandwidth
speedtest # speedtest CLI
🔧 Troubleshooting Flow
# Site not loading?
1. ping site.com → reachability
2. dig site.com → DNS
3. curl -v https://site → full request
4. ss -tulnp | grep 443 → listening?
5. tail -f nginx logs → server logs
6. ufw status → firewall block?
7. systemctl status nginx → service running?
🎓 মূল কথা ⭐
5 command = 90% network debug — ping, dig, curl, ss, traceroute। Server unreachable → ping। Site error → curl -v। Port → ss/lsof।