I just realized I don't know traceroute as well as I thought I did. apparently Unix systems send UDP packets, while Windows sends ICMP. which maybe explains why I've had such a miserable experience with traceroute on the modern Internet, because many ISPs block ICMP from outside.
I’ve never encountered an isp blocking icmp that doesn’t also block all sorts of traffic. I can ping 8.8.8.8 or whatever from almost every connection I’ve used anywhere in the world.
Not every router will return a tel expired of course, and many ISPs route ipv4 traffic via rfc1918 addresses nowadays , so you can get big gaps in their networks, but that applies whether your outbound packet is icmp, tcp, UDP, or any other type.
Worth remembering that packets with different source and destination ports can route via different paths, so sometimes you need to be aware of the entire ip/port/protocol for src/dst and configuring them properly. Nat can cause problems there too when it changes your source ports.
