[mccoyc]

Traceroute works by observing Internet Control Message Protocol (ICMP) time to live/hop count exceeded messages and noting the source IP of those messages. There's plenty of resources you can search on to learn more about this. When you see * * *, it means that for that given TTL value, no corresponding ICMP messages were returned to the source.

It could be because they were filtered at the boundary of the network. If source IPs are private (RFC-1918 or carrier grade NAT space), those ICMP messages should get dropped. This is Best Current Practice (BCP) 38, if you wanted to read more about it.

Ever want to know why IPv6 is so important? This is another reason why. Troubleshooting networks without globally significant IP addresses on the intermediate hops is a real pain.

[spelunker]

Great info, ty!