On Thu, 17 Oct 2002, k claffy wrote:
remark it is also possible for the (forward or reverse) path to change in the middle of the measurement, such that traceroute output would lead you to believe a path that never existed anywhere on the Internet (i.e., one that is not manifested in the current physical Internet) and you would not be able to confirm for sure without asking the contacts for the IP links in question how they're connected.
Although I've only seen it as part of an April's Fool prank, it is possible to do amazingly evil things to traceroutes, Whitehouse.Gov going through Kremvax.Su Truth is such an elusive thing. Not only do you need to worry about the network changing while you are measuring it, you also need to worry about the network telling you the truth about what happened to the packet.
traceroute is a disconcertingly blunt hammer; that we continue to use it to essentially nail moving jello to a wall says more about us than about anything on the Internet (and is quite the testimony to van who thought it up and implemented it in a few hours 20 years ago and noone has come up with anything better since.)
People have come up with other ways of tracing routers through a packet network, snmptrace, ip record route, beacon packets. But they all have limitations compared to Van Jacobson's traceroute. A testiment to the power of traceroute is its now considered necessary functionality for any data network, not just TCP/UDP/IP networks. OSItraceroute, MPLStraceroute, ATMtraceroute, DECNETtraceroute, etc.