traceroute uses UDP by default, not ICMP

At least on Linux. Don’t believe me? Run tcpdump -nn -i <interface> 'host example.com' in one shell and traceroute example.com in another. tcpdump will pick up all 3 of {ICMP, UDP, TCP}, and on my machine the pattern is clear: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20:58:47.187086 IP 1.2.3.4.41369 > 93.184.216.34.33434: UDP, length 32 20:58:47.187160 IP 1.2.3.4.39830 > 93....

November 29, 2023