[svlug] Re: backbone packet loss...

Scott Hess scott at doubleu.com
Thu Oct 23 22:12:47 PDT 2003


One thing I realized this morning when I was having bad loss (I had it 
yesterday, too), is that mtr is very different outgoing (from your host to 
the world) than incoming (from some other Internet host to your host) if 
the loss is happening near you.  Mine was happening between myself and my 
ISP, so if I mtr'ed myself from work, I'd see lots of good hops and a 
final 33% loss.  If I mtr'ed work from home, I'd see >33% loss on every 
link, because of the root loss on my initial hop.

Still, it weirded me out for just a minute, there.

Later,
scott

On Thu, 23 Oct 2003, George Georgalis wrote:
> On Wed, Oct 22, 2003 at 10:39:38AM -0700, Cory Petkovsek wrote:
> >On Wed, Oct 22, 2003 at 12:55:50PM -0400, George Georgalis wrote:
> >> I'm seeing intermittent but severe (40-60%) packet loss on various
> >> backbone hops...
> >> 
> >> Is there some <cough, cough> virus going around?
> >
> >More likely one of your upstream routers is broken.  Packets through one
> >route get through, packets through the other do not, and the routing
> >algorithm is alternating between the two.  I've seen it happen through
> >my cable isp a few times.  Ping google.com and I get seq 1,3,5,7,9,11..
> >etc back.  Use traceroute to figure out which one it is (figure out your
> >path(s), then ping each step until you experience packet loss).  Then
> >call your isp.
> 
> 
> I don't know what it was but it seemed to end about 1:30pm EST.  I was
> using mtr to generate a report ever few minutes. Yeah, Cory, the route
> was changing on each test. The really odd thing is the loss was starting
> at the "deepest core" routers (and emergency ones), as far as I can
> tell.
> 
> What follows is not an actual report but lines from worst of them, at
> the hop where the loss started.
> 
> 
> HOST                                    LOSS  RCVD SENT    BEST     AVG   WORST
> 
> unknown.Level3.net                       90%     1   10   10.11   10.11   10.11
> 
> 198.32.160.61                            60%     4   10    5.18    5.34    5.51
> 
> nyiix.tycho.net                          80%     2   10  149.08  200.43  251.77
> 
> ???                                     100%     0   10    0.00    0.00    0.00
> 
> 
> At one point I couldn't get dns for a (deep) hop, and unknown.Level3.net
> or 198.32.160.61 in the route is not at all normal either -- but they
> worked today ;-).
> 
> // George
> 
> 
> 





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