> There are now things like MPLS, which operate by encapsulating IP […] Without getting much further into how that works: It is completely impossible for it to

> There are now things like MPLS, which operate by encapsulating IP […] Without getting much further into how that works: It is completely impossible for it to satisfy the expectations of traceroute. The author probably should've gotten at least a bit further into how that works, because it is absolutely possible to get an IP traceroute across an MPLS backbone. It works in a slightly curious way - the MPLS payload (original IP packet) is replaced with the ICMP message, but the packet continues to progress forward rather than "turning around"; it only "changes direction" at the end of the MPLS domain. A good number (yes, not all) commercial router vendors implement this.