North American Network Operators Group
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Re: Phantom packet loss is being shown when using pathping in connectionwith asynchronous routing - although there is no real loss.

  • From: Michael.Dillon
  • Date: Wed Jun 07 06:05:43 2006 
> The only part that I don't get is that you can mtr to him without 
> packetloss.  Although the path in-between may be different, the final 
hop 
> packetloss should exactly equal what he sees when mtring you.  A 
round-trip 
> is a round-trip, and results should be identical regardless of who 
> originates.  I can't think of any way this would be different unless 
echo 
> and echo-reply were being rate limited independently.

If the time was different then the packet loss would
be different. Perhaps the customer runs the tests during
his busy period when he is concerned about making sure
there is no delay. Then, later in the day, after his busy
period is over he takes the time to contact his ISP. The ISP
then runs some tests which show there is no packet loss
at all. To be sure this is not happening, synchronize the
tests and run simultaneously.

Try tcptraceroute because this more accurately reflects
the traffic that is flowing. 
http://michael.toren.net/code/tcptraceroute/

http://tracetcp.sourceforge.net/ is a windows tool
that is similar.

The open source tool LFT can be built to run on Windows
under cygwin http://pwhois.org/lft/ but they have this
warning on their page:

   Many people have complained about various problems on 
   the Windows platform. Both LFT and the WhoB client 
   compile and run well under Cygwin environments on 
   Windows. Unfortunately, Microsoft's changes to the 
   Windows IP stack (as of XP Service Pack 2) reduced 
   their raw socket functionality significantly as part 
   of their security bolstering process. These changes 
   have effectively stopped LFT from working properly 
   while using TCP. LFT's UDP tracing and other advanced 
   features still work properly. For more information on 
   Windows raw sockets, consult 
 
www.microsoft.com/technet/prodtechnol/winxppro/maintain/sp2netwk.mspx#EIAA 


This may have nothing to do with your MTR issue but it
does make one wonder whether a Windows machine is safe
to do performance testing. In any case, the LFT people
think that their non-TCP features still work properly
on Windows and this is a tool that you can also run
on your end. Worth a try?

--Michael Dillon