Networking

Ports & Processes

lsof -i:PORT_NUMBER          # which process holds a port
lsof -nP -iTCP -sTCP:LISTEN  # all listening TCP sockets

DNS & HTTP

dig +short example.com         # resolve A record
dig example.com MX             # mail records
curl -I https://example.com    # response headers only
curl -sS -o /dev/null -w '%{http_code} %{time_total}s\n' https://example.com

Discovery & Scanning

# Scan local network for IPs and names (brew install arp-scan)
sudo arp-scan --interface=en0 --localnet
 
nmap -sn 10.0.0.0/24                # host discovery (ping sweep)
nmap -sT -p 80,443 10.0.0.0/24      # TCP connect scan (use -sS for SYN/stealth, needs sudo)
nmap -A 10.0.0.115                  # OS + service/version detection
nmap --script vuln <ip>            # vulnerability scripts

Path & Reachability

traceroute example.com
ping -c 4 example.com
nc -vz host 443                     # test if a TCP port is open

Only scan networks you own or are authorized to test.