From: simon hart (simon@harttel.com)
Date: Sun Sep 18 2005 - 12:53:24 GMT-3
Hi Group,
Sorry, but I have reread this again (with the Doc CD) and need to retract
most of this question.
I failed to realise that the marking action takes over in CAR, thus anything
over either 128k or 256k is going to get marked and not dropped. There
should be no drop action within the MQC statements.
However I do believe that there are still errors within this scenario, in
particular CAR and MQC behave differently and therefore to achieve the same
ends is somewhat diffilcult.
Simon
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of simon
hart
Sent: 18 September 2005 16:05
To: Group Study
Subject: QOS IE Workbook Lab 13 Q.9.1
Hi All,
I would welcome comments on this task within the IE workbook. I think that
the question and answer may be incorrect,
The task itself is to change various CAR statements into MQC. The problem I
see here is that CAR and MQC have different policing algorithms and thus to
mimic each statement is extremely diffilcult.
One is asked to achieve the following
rate-limit input access-group 101 128000 2000 2000 conform-action transmit
exceed-action set-prec-transmit 0
The answer given for the MQC statement is as follows
police cir 128000 bc 2000 be 2000
conform-action transmit
exceed-action set-prec-transmit 0
Now I believe this answer to be wrong for the following reasons. When the
bc and be are equal within CAR there is no burst, thus no exceed action.
Although the CLI for CAR will accept the 'exceed-action set-prec-transmit 0'
there is in fact no burst and thus no exceed action.
However when entering the command within MQC we have a problem if we mimic
the CAR statements. Because MQC uses a single rate three colour marker it
has two discrete token buckets. By setting bc and be we are setting the
values for each token bucket and hence enabling an exceed action. Therefore
we are allowing a burst action that will set the precedence of 0, however
the CAR statement does not allow that.
I believe the correct answer would be
police cir 128000 bc 2000
conform-action transmit
exceed-action drop
One is also asked to perform the following
rate-limit input access-group 102 256000 4000 8000 conform-action transmit
exceed-action set-prec-transmit 0
The answer given for this in MQC is:
police cir 256000 bc 4000 be 8000
conform-action transmit
exceed-action set-prec-transmit 0
For similar reasons that I gave above I believe that this answer is also
incorrect. I believe that the correct answer should be
police cir 256000 bc 4000 be 4000
conform-action transmit
exceed-action set-prec-transmit 0
violate-action drop
The CAR statement implies a burst of 4000 (the difference between 4000 and
8000), therefore within MQC bc and be should be 4000 a piece. In addition
one has to create a violate-action otherwise the circuit will never be
limited to an average of 256000 as the exceed action will be used on all out
of contract traffic.
Other views most welcome
Simon Hart
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