Network Debug
When to use
Use this skill when the user needs to:
- •Test connectivity (ping, traceroute)
- •Debug DNS resolution
- •Check open ports and listening services
- •Make HTTP requests
- •Diagnose firewall issues
- •Inspect network interfaces
Connectivity
Basic tests
bash
ping -c 4 8.8.8.8 # test raw connectivity ping -c 4 google.com # test DNS + connectivity traceroute google.com # trace path mtr --report google.com # combined ping + traceroute
DNS
bash
nslookup example.com dig example.com dig +short example.com A host example.com cat /etc/resolv.conf # DNS config
Ports and services
Check listening ports
bash
ss -tlnp # TCP listeners ss -ulnp # UDP listeners netstat -tlnp # alternative lsof -i :80 # what's on port 80
Test remote ports
bash
nc -zv host 80 # check if port is open curl -v http://host:port # HTTP test timeout 3 bash -c 'echo > /dev/tcp/host/port' && echo "open"
Network interfaces
bash
ip addr show # all interfaces ip route show # routing table ip link show # link status ifconfig # legacy
HTTP debugging
bash
curl -v https://example.com # verbose
curl -o /dev/null -s -w '%{http_code}' URL # status code only
curl -H "Content-Type: application/json" -d '{}' URL
wget --spider URL # check if URL exists
Firewall
bash
sudo iptables -L -n -v # list rules sudo ufw status # UFW status sudo ufw allow 80/tcp # allow port
Common issues
- •Connection refused: Service not running on target port
- •Connection timed out: Firewall blocking, wrong IP, or host down
- •Name resolution failed: DNS misconfigured, check
/etc/resolv.conf - •Network unreachable: Routing issue, check
ip route