🚀 go-pugleaf

c9219517@cs.newcastle.edu.au (Scott Howard) writes:
>For some reason, traceroute and apple.com.au do not go together. You might
>notice that there are 8 valid hosts above, followed by 8  * * *  hosts (ie,
>hosts which did not reply). It's not a coincidence that those two numbers
>happen to be the same - no matter where you traceroute apple.com.au from you
>get exactly the same pattern.

This symptom is even documented in the traceroute manpage:

     bug  in  the  4.[23]BSD  network code (and its derivatives):
     4.x (x <= 3) sends an unreachable message using whatever ttl
     remains  in the original datagram.  Since, for gateways, the
     remaining  ttl  is  zero,  the  ICMP  "time   exceeded"   is
     guaranteed  to not make it back to us.  The behavior of this
     bug is slightly more interesting when it appears on the des-
     tination system:
 
           1  helios.ee.lbl.gov (128.3.112.1)  0 ms  0 ms  0 ms
           2  lilac-dmc.Berkeley.EDU (128.32.216.1)  39 ms  19 ms  39 ms
           3  lilac-dmc.Berkeley.EDU (128.32.216.1)  19 ms  39 ms  19 ms
           4  ccngw-ner-cc.Berkeley.EDU (128.32.136.23)  39 ms  40 ms  19 ms
           5  ccn-nerif35.Berkeley.EDU (128.32.168.35)  39 ms  39 ms  39 ms
           6  csgw.Berkeley.EDU (128.32.133.254)  39 ms  59 ms  39 ms
           7  * * *
           8  * * *
           9  * * *
          10  * * *
          11  * * *
          12  * * *
          13  rip.Berkeley.EDU (128.32.131.22)  59 ms !  39 ms !  39 ms !
 
     Notice that there are 12 "gateways" (13 is the final  desti-
     nation)  and  exactly  the  last half of them are "missing".
     What's really happening is that rip  (a  Sun-3  running  Sun
     OS3.5)  is  using  the ttl from our arriving datagram as the
     ttl in its ICMP reply.  So, the reply will time out  on  the
     return  path  (with  no  notice  sent to anyone since ICMP's
     aren't sent for ICMP's) until we probe with a ttl that's  at
     least  twice  the  path  length.  I.e., rip is really only 7
     hops away.  A reply that returns with a ttl of 1 is  a  clue
-- 
David Wilson	Dept CompSci Uni Wollongong Australia	david@cs.uow.edu.au