Silently dropping QoS marked packets on the greater Internet

Valdis.Kletnieks at Valdis.Kletnieks at
Fri Sep 2 16:02:03 UTC 2011

On Fri, 02 Sep 2011 17:48:17 +0300, Saku Ytti said:

> Seems in this instance someone has deployed QoS and is trusting markings from
> Internet, which is just broken, as they cannot anymore guarantee that customer
> video/voice etc works during congestion, so the QoS product is broken.

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.  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.

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

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