From: shank shank (shankshink@yahoo.com)
Date: Mon Dec 01 2008 - 18:40:00 ARST
i guess what i was trying to understad that is when the priority command is
applied to certain calss can we think of this as a way to limit the bandwidth
to that class to whatever bandwidth configured. i thnk this what anthony
confirmed. or is it conditioned on the congestion status of the interface?
________________________________
From: Scott M Vermillion
<scott_ccie_list@it-ag.com>
To: paul cosgrove <paul.cosgrove@gmail.com>
Cc:
Anthony Sequeira <asequeira@internetworkexpert.com>; shank shank
<shankshink@yahoo.com>; CCIE Group <ccielab@groupstudy.com>
Sent: Monday,
December 1, 2008 3:00:46 AM
Subject: RE: Priority command
> The link
mentions that "During
congestion conditions, a priority class cannot use any
excess bandwidth".
Perhaps that is what you are thinking of.
Thats
precisely what I was thinking of Paul!
;-)
Now
this whole thing gets
interesting when you really ponder the definition of congestion.
Its
tempting to think that 129 kbps of traffic presenting to an
interface clocked
at 128 kbps equals/leads to congestion (which it obviously
does) and leave it
at that. But congestion actually occurs
in scenarios where you havent even
reached your interface clock
rate! As I understand things, anyway. For the
purposes of QoS,
congestion means that your TxRing is full and has backed up
into the configured
SW queue(s). Depending on TxRings depth and the
burstiness of the
traffic, it may well fill quickly (and recall that the very
act of configuring
a SW queue on an interface automatically results in its
TxRing being truncated
so as to invoke the SW queue more readily).
So
I
think if you had an interface running at 100 Mbps and you configured a
priority class of 10 Mbps, then presented nothing but the priority class of
traffic to that interface, youd likely see greater than 10 Mbps of
throughput
but less than 100 Mbps, depending on the nature of the traffic itself
(and to
an extent I can see there being platform-specific and interface
type-specific
differences). I would expect the SW queue to be invoked at
some point, the
priority-class to be policed, and then the SW queue to be
released for a
period, so on and so on
(may
just be a good lab to put together at some
point)
-----Original Message-----
From: nobody@groupstudy.com
[mailto:nobody@groupstudy.com] On Behalf Of
Anthony Sequeira
Sent: Sunday,
November 30, 2008 12:25 PM
To: shank shank
Cc: CCIE Group
Subject: Re:
Priority command
Yes - the priority command is used with Low Latency Queuing
(LLQ) and
it specifies the amount of priority bandwidth to provide to a type
of
traffic (typically Voice). This command also causes a POLICING to the
amount of bandwidth specified..
This is a mechanism to guard against queue
starvation for other
traffic forms.
Anthony J. Sequeira, CCIE #15626, CCSI
#23251
Senior CCIE Instructor
asequeira@internetworkexpert.com
Internetwork
Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987
Outside
US: 775-826-4344
On Nov 30, 2008, at 1:33 PM, shank shank wrote:
> hello,
>
quick question experts: does the priority command apply a
> maximum limit when
specifying a bandwidth? or is it applying the
> minimum bandwidth certain
class can get in the policy?
>
> so does this command priority 100 means that
the maximum bandwidth
> the class will get is 100k?
>
>
> according to this
link
http://www.ciscosystems.com/application/pdf/paws/10100/priorityvsbw.pdf
>
it does both. can anyone clarify this to me. thanks,
>
>
> Blogs and organic
groups at http://www.ccie.net
>
>
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