Re: [LARTC] Parameters for the ingress qdisc?

["Martin A. Brown" <mabrown-lartc@securepipe.com>]

 : OK - This is very interesting to me. I understand the mechanism whereby
 : filters guide packets to the classes for which they are destined. That
 : all makes sense.
 :
 : Based on what I've read here, it sounds like you can interpose a
 : policer between the filter itself and the class to which it is
 : directing packets. Given that classes already have access to the full
 : range of qdiscs, with all their marvelous dials and knobs, interposing
 : a policer seems superfluous. Have I misunderstood?

Well, I wouldn't say superfluous.....and I don't think you have
misunderstood, but perhaps you don't yet see the rationale for a policer.
Let me suggest a scenario.  You have users who send mail.*  You wish
to guarantee a certain small percentage of your 2Mbit to only the SMTP
traffic, so that at least 256kbit is reserved for mail at any time.
Additionally, you want to put any SMTP flows above this 256kbit into a
general consumption class.

Well, your policer reclassifies any traffic above a given rate into the
general consumption class.

That's just one way of using a policer.  My understanding is that policers
are more commonly used for DiffServ domains and limiting inbound traffic,
although there's nothing preventing them from being used in ingress
traffic situations.

-Martin

 * I know it sounds incredible for me to suggest that a network admin
   might have users, but suspend your disbelief for now, if you can.

-- 
Martin A. Brown --- SecurePipe, Inc. --- mabrown@securepipe.com

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