[144346] in North American Network Operators' Group
Re: Silently dropping QoS marked packets on the greater Internet
daemon@ATHENA.MIT.EDU (Mark Tinka)
Fri Sep 9 01:16:56 2011
From: Mark Tinka <mtinka@globaltransit.net>
To: nanog@nanog.org
Date: Fri, 9 Sep 2011 13:16:18 +0800
In-Reply-To: <6403.1314979323@turing-police.cc.vt.edu>
Reply-To: mtinka@globaltransit.net
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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On Saturday, September 03, 2011 12:02:03 AM=20
Valdis.Kletnieks@vt.edu wrote:
> Except you can't actually *guarantee* that QoS works
> every packet, every time, during congestion even within
> the same network. Remember - QoS is just a marking to
> shoot the other guy first. If a link ends up
> overcommitted with QoS traffic, you're still screwed.=20
> And there's a second-order effect as well - if your net
> is running sufficiently close to the capacity edge that
> QoS actually matters, there's probably other engineering
> deficiencies that are just waiting to screw you up.
Agree.
What we've seen (and I suppose what the design philosophy=20
suggests) is that so-called Priority traffic has the highest=20
chance of survival during times of evil. But then again,=20
depending on just how saturated the port queues are, even=20
Priority traffic can get dropped due to lack of buffers -=20
that is if it hasn't already been caught by policers that=20
tend to go along with Priority queues.
> Is the story I've heard about people managing to saturate
> a link with QoS'ed traffic, and then having the link
> drop because network management traffic was basically
> DoS'ed, apocryphal, or have people shot themselves in
> the foot that way?
This sounds like a hacked attempt to get management to=20
approve that 40Gbps upgrade :-).
Mark.
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