Network Diagnostics

Diagnose network issues using standard cross-platform tools.

Connectivity Check

Ping host:

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exec: ping -c 4 example.com

Quick reachability test:

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exec: ping -c 1 -W 3 8.8.8.8 && echo "Online" || echo "Offline"

DNS Lookup

Basic lookup:

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exec: dig example.com +short

Full record:

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exec: dig example.com

Specific record type:

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exec: dig example.com MX +short

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exec: dig example.com AAAA +short

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exec: dig example.com TXT +short

Reverse DNS:

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exec: dig -x 8.8.8.8 +short

Using specific DNS server:

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exec: dig @1.1.1.1 example.com +short

Fallback (if dig not available):

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exec: nslookup example.com

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exec: host example.com

Route Tracing

Traceroute:

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exec: traceroute -m 20 example.com

On Linux (may need traceroute package):

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exec: traceroute example.com

macOS alternative:

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exec: traceroute -q 1 example.com

Port Checking

Check if a port is open:

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exec: nc -zv -w 3 example.com 443 2>&1

Scan port range:

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exec: for port in 22 80 443 3306 5432 6379 8080; do nc -zv -w 2 example.com $port 2>&1; done

Check local listening ports:

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exec: ss -tlnp 2>/dev/null || netstat -tlnp 2>/dev/null || lsof -i -P -n | grep LISTEN

Public IP

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exec: curl -s ifconfig.me

Detailed IP info:

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exec: curl -s ipinfo.io/json

Network Interfaces

List interfaces:

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exec: ip addr 2>/dev/null || ifconfig

Active interface and gateway:

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exec: ip route 2>/dev/null || netstat -rn | head -10

Bandwidth Test (Simple)

Download speed:

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exec: curl -s -o /dev/null -w "Speed: %{speed_download} bytes/sec\nTime: %{time_total}s\nSize: %{size_download} bytes\n" https://speed.cloudflare.com/__down?bytes=10000000

Whois

Domain info:

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exec: whois example.com | head -40

SSL/TLS Certificate

Check certificate:

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exec: echo | openssl s_client -connect example.com:443 -servername example.com 2>/dev/null | openssl x509 -noout -dates -subject -issuer

Certificate expiry only:

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exec: echo | openssl s_client -connect example.com:443 -servername example.com 2>/dev/null | openssl x509 -noout -enddate

HTTP Headers

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exec: curl -sI https://example.com

Active Connections

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exec: ss -tnp 2>/dev/null || netstat -tn

Connection count by state:

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exec: ss -tn 2>/dev/null | awk '{print $1}' | sort | uniq -c | sort -rn || netstat -tn | awk '{print $6}' | sort | uniq -c | sort -rn

Notes

•ping, curl, openssl are available on nearly all systems.
•dig may need dnsutils (Linux) or bind-tools package.
•traceroute may need traceroute package on minimal Linux installs.
•ss is the modern replacement for netstat on Linux; netstat works on macOS.
•Some commands may require sudo (e.g., tcpdump, certain nmap scans).
•The nc (netcat) command syntax varies slightly between macOS and Linux.