Anyone from Verizon/TATA on here? Possible Packet Loss

Jay Ashworth jra at baylink.com
Thu Sep 27 01:11:16 UTC 2012


----- Original Message -----
> From: "Derek Ivey" <derek at derekivey.com>

> I'm at home now. I also have Verizon FiOS and believe I am seeing the
> same thing our client saw. So you guys are saying that the response
> times in traceroutes might not always be accurate because routers
> prioritize ICMP messages. Does that mean values from MTR aren't
> accurate? I fired up MTR and took 2 screenshots
> (http://imgur.com/a/RDyXO). What do you guys think? Most of the time
> the ping times seem fairly low, however I occasionally see these spikes.
> It seems sporadic...

To recap, traceroute, mtr, and similar utilities work by talking to each
succesive router along a path.  Because this is so, and because Any Given 
Router may be too busy to deal with such packets in favor of "real" traffic
(most routers handle data packets on the line cards, while they may have
to expend actual CPU on things like ICMP), it's possible for a path with 
perfect connectivity to show some intermediate hops completely missing --
No Reply At All, you might say -- to diagnostic tools.

The traces you show look pretty decent; I've seen much worse on links
with fine interactive shell session response.  The time you have to 
worry is when one router *and everything past it* shows packet loss of
roughly the same amount, or when ping times jump markedly at a given 
spot (by which I mean, say, from 32 to 800ms, rather than from 32 to 125).

The short version, though, which most people are are being uncharacteristically
too nice to say (:-) is that this is still a tier 1 problem, and NANOG is
generally tier 3 or 4.  :-)

You're welcome to take the issue up over on outages at outages.org, if you
like...

Cheers,
-- jra
-- 
Jay R. Ashworth                  Baylink                       jra at baylink.com
Designer                     The Things I Think                       RFC 2100
Ashworth & Associates     http://baylink.pitas.com         2000 Land Rover DII
St Petersburg FL USA               #natog                      +1 727 647 1274



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