# Simulated output of network diagnostic commands

$ ss -tlnp | grep 5432
# (no output — nothing is listening on port 5432 locally)

$ nc -zv db.internal.example.com 5432
nc: connect to db.internal.example.com (10.0.1.50) port 5432 (tcp) failed: Connection timed out

$ ping -c 3 db.internal.example.com
PING db.internal.example.com (10.0.1.50) 56(84) bytes of data.
64 bytes from 10.0.1.50: icmp_seq=1 ttl=64 time=0.5 ms
64 bytes from 10.0.1.50: icmp_seq=2 ttl=64 time=0.4 ms
64 bytes from 10.0.1.50: icmp_seq=3 ttl=64 time=0.5 ms
# Server is pingable but port 5432 is blocked!

$ iptables -L INPUT -n | grep 5432
# (no output — no firewall rule allowing port 5432)
# NOTE: A firewall rule change was applied Friday at 23:00 during maintenance.
# The rule allowing port 5432 from this server was accidentally removed.
