ICMP flood
DDoS via massive ICMP Echo Request packets (ping). Classic but outdated — modern infrastructure rate-limits ICMP aggressively. Historically: Smurf attack used broadcast amplification.
Smurf: send ICMP Echo to the network's broadcast address with spoofed source = victim → all hosts in the broadcast domain reply to the victim. Crushed massive sites in the 90s. RFC 2644 (1999): routers should NOT forward directed broadcasts by default → mostly mitigated. Modern ping flood: just pure volume, easier to defend. Edge firewall drops ICMP volume. ICMP is still necessary for PMTUD and traceroute — total block breaks network functionality.