My kids complained today that Google Classroom isn't working. After a quick investigation, I noticed that Snort on my firewall blocked the relevant Google server due to incoming TCP port scans. Sigh.
Be careful with automated rules - unless it's a full TCP handshake, you can't conclusively identify the source of a port scan as the IP may be spoofed. If someone port scanned you and spoofed eg the IPs of your DNS servers, you've self-DoSed yourself.