Re: [LARTC] Parameters for the ingress qdisc?

From: "Martin A. Brown" <mabrown-lartc@securepipe.com>
To: lartc@vger.kernel.org
Subject: Re: [LARTC] Parameters for the ingress qdisc?
Date: Thu, 07 Aug 2003 01:37:28 +0000	[thread overview]
Message-ID: <marc-lartc-106022038607629@msgid-missing> (raw)
In-Reply-To: <marc-lartc-106011742407167@msgid-missing>

Patrick,

As far as I'm concerned, these are two very good questions.

 : 1) When working with egress traffic control, filters are attached to
 :    classes. The documents I've read so far tell me that the ingress
 :    qdisc is classless so, on the face of it, filters shouldn't be
 :    useable at all.  Please tell me which part of this I have badly
 :    misunderstood.

Agreed....it doesn't make sense, to me, except as code reuse.  Any takers
care to explain why this is?

 : 2) Since the filters themselves are, as you say, stateless, then it
 :    sounds like a "policer" is a separate object that's being created at
 :    the same time as the filter. Is there any other way to create a
 :    "policer" object, or do they only exist when attached to filters?

My understand is that the policers only exist attached to filters.  They
are separate, but not able to be generated without a filter.  I think
Stef's description isn't so bad....a policer is similar to a token bucket
filter (TBF) which is attached to a filter.  I don't know what it looks
like inside the policing code, so I'll have to assume that this is
correct.  From the outside of the black box, they are pretty much rate
limiters which you can attach to any "tc filter" command.

 :    When working with egress traffic control, can you attach policers
 :    to filters,

Yes.

 :     and how would they interact with the classes?

When a new packet arrives on an output queue prior to outbound traffic
control (but after netfilter POSTROUTING), the packet will first traverse
the filters attached to qdisc 1:0 to learn of its destination flowid.
Here, you could have a number of different filters which classify and/or
reclassify the packet into different output classes/qdiscs.  You could
optionally drop packets with a filter here, just as you could drop packets
with filters on the ingress qdisc.

These policers will be VERB (executed? obeyed?) before the packet ever
enters the classes and sub-classes.

-Martin

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

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