probe loss rates, calculation of

John Snell (geigudr@cs.washington.edu)
Wed, 24 Jun 1998 19:50:57 -0700 (PDT)

Time to put my logic up for question. Traceroute sends out 3 probes, with
increasing TTL. The question is, how many of the probes do we attribute
to the target? Not as easy as it might look:

(Note that it's common (enough) in the traces, to have a given targetIP
respond as something else; ie, I trace to 128.95.2.175, and 128.95.2.173
responds, and traceroute accepts that as good.)

/* There are four cases to consider here:
1. The current TTL is not the max; then traceroute recieved a
response from
someone identifying themselves as the recipient. Take all failed
probes
at this TTL, plus all failed probes from all TTLs previous, where
such
a previous TTL had nothing resolve. (ie, * * *)

2. The current TTL is max, and nothing resolved. Then take all such
complete failures, moving back, until at least one IP resolved
for
a given TTL, this last non-inclusive.

3. The current TTL is max, and the precise target resolved. Then
treat this as
case 1.

4. The current TTL is max, and something resolved, but it wasn't the
precise target.
Then we don't know, as this could either be a logical proxy for
the target, or
it could be something else. Punt.
*/

Does this cover all the bases?

Thanks,
John

_____________________________________________________________________________
"The human mind is a 400,000-year-old legacy application...and you expected
to find structured programming?" -- Randall Davis, 1996 AAAI Pres. Address