From: Stemberger, Gregory J [NTK] (greg.x.stemberger@mail.sprint.com)
Date: Tue Apr 12 2005 - 01:13:16 GMT-3
Please see the following link that briefly discusses putting voice and video in the strict priority queue and the behavior of multiple priority queues:
When you configure multiple LLQ's, only a single strict priority queue really exist, so there is really is not a question of order. The way I look at it is that all of the traffic in the priority queue gets immediate access to the tx-ring and therefore gets transmitted via a FIFO algorithim in the order it arrived to the router.
There probably are exceptions.....One exception that I can think of is, packets unexpectedly getting punted to process switching and creating an situation in which packets will be transmitted out of order.
The added value of configuring multiple priority queues, is to provide the ability to police different traffic accordingly to control the usage of the strict priority queue. Configuring multiple priority queues definitely has it's place depending on the network design and requirements.
Gregory Stemberger
CCIE #10133 R/S+Security
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
stephen skinner
Sent: Monday, April 11, 2005 5:37 AM
To: simon hart
Cc: Jelle Borsje; ccielab@groupstudy.com
Subject: Re: priority command in MDQ
ok guys ,
if that`s the case , which is the highest prioirty ,prioirty queue. ??
E.G
all of the below class are important ,and must have prioirty over non
selected traffic.
if i create 3 prioirty queue`s which one is the important one ?
class 1
permit voice
class 2
permit telnet
class 3
permit http
policy-map me
class class 1
prioity 100
class class 2
prioirty 100
class class 3
priority 100
which prioirty queue gets serviced first ? .
TIA
steve
On Apr 9, 2005 9:20 AM, simon hart <simon.hart@btinternet.com> wrote:
> Jelle,
>
> Thanks for the link and the test. After Tim's mail I tried it too and to my
> surprise it accepted more than one priority. Well, one does live and
> learn!!
>
> S.
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Jelle Borsje
> Sent: 08 April 2005 15:35
> To: ccielab@groupstudy.com
> Subject: RE: priority command in MDQ
>
> Hej,
>
> Interesting. I also throught there could only be one
> priority queue, but I was wrong. I just tried it on a
> router, and it accepted 4 priority queues in the
> policy-map (didnt try more). In the following link
> Cisco is actually stating that it can be configured on
> multiple links, but should only be used for
> voice-like, constant bit rate traffic.
>
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121newft/121
> t/121t3/dtcfgbst.htm
>
> The link here explains what the difference is between
> queues defined with the priority and bandwidth
> commands:
>
> http://www.cisco.com/warp/public/105/priorityvsbw.html
>
> The 2 types of queues are intended for 2 very
> different types of traffic, and have therefore
> completely different characteristics. A strict
> priority queue cannot exceed the configured bandwidth
> during congestion, while a queue configured with the
> bandwidth statement can. A policy-map is not
> restricted to only 1 priority queue it seems.
>
> Greetz
> Jelle
>
> --- ccie2be <ccie2be@nyc.rr.com> skrev:
> > Hi Simon,
> >
> > Actually, according to Wendell Odom, you can have 2
> > priority queues. I
> > don't remember all the details or how scheduling is
> > done between the 2
> > priority queues but it should work.
> >
> > I've never tried it, but I wonder what happens when
> > 2 priority queues are
> > configured and then 3 priority queues are
> > configured.
> >
> > Would IOS take the 3rd priority queue command or
> > would it give you an error
> > message?
> >
> > It's interesting to think about but probably not
> > that relevant in terms of
> > the lab.
> >
> > Tim
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com
> > [mailto:nobody@groupstudy.com] On Behalf Of
> > simon hart
> > Sent: Friday, April 08, 2005 7:48 AM
> > To: steve.skinner@uk.pwc.com; ccielab@groupstudy.com
> > Subject: RE: priority command in MDQ
> >
> > Steve,
> >
> > With CBWFQ/LLQ, the order by which you enter the
> > classes/queues does not
> > dictate the manner by which the traffic is
> > scheduled, with the exception of
> > the priorirty queue,
> >
> > With CBWFQ without a priority queue and under
> > congestion conditions each
> > queue is 'dequeued' to the configured bandwidth
> > command. The exact manner
> > by which the scheduler takes this packets and puts
> > them onto the TX-ring of
> > the interface is proprietary and has not been
> > published by Cisco, therefore
> > we can only guess at this particular scheduling for
> > each queue ( I expect
> > the manner by which each queue is serviced is
> > similar to WRR).
> >
> > Now by configuring a Priority queue, you are
> > changing the scheduling of the
> > CBWFQ somewhat. The Priority queue will get
> > serviced first, if their are
> > packets in its queue, up to it's configured
> > bandwidth. Once the Priority
> > queue has been dealt with the scheduler will now
> > service the other queues in
> > the manner described previously.
> > This type of queueing is important for latency
> > sensitive applications such
> > as Voice or Video.
> >
> > A couple of points on the priority queue,
> >
> > 1. You can only have one priority queue (you
> > configuration is incorrect in
> > this regard.)
> > 2. The priority queue should only represent 30% of
> > the Max Reserved
> > Bandwidth of the Interface. You can go higher,
> > however you can run into
> > problems, it is not unknown for the CPU to sky
> > rocket under such conditions.
> > 3. You should only put one type of traffic in the
> > Priority queue. If you
> > are trying to deliver a Voice service (under an
> > SLA), then you want to make
> > sure that the voice is behaving as expected, if you
> > mix it up with other
> > traffic (such as Video), you cannot guarentee
> > latency and jitter of the
> > voice traffic.
> > 4. The priority command does not define a strict
> > priority for scheduling
> > each class.
> >
> >
> > Your Policy below will be doing this
> >
> > VOIP will be policed at 1Mbps and conforming traffic
> > marked as IPprec 4
> > (Flash Override)
> >
> > Backup Servers will be policed at 250Kbps
> >
> > All other traffic will be marked with IPprec 5
> > (Critical)
> >
> > Under congestion conditions your VOIP will be
> > guaranteed 1Mbps and this
> > 1Mbps will be dequeued before any other traffic.
> >
> > Your other two queues do not have any bandwidth
> > configured, therefore under
> > congestion conditions the BackupServer and Class
> > Default queue will compete
> > for bandwidth. However under these conditions the
> > BackupServer will only
> > 'compete' up to its policed rate. I would suggest
> > entering a bandwidth
> > command on the BackupServer class in order to
> > guarentee its policed rate.
> >
> > Your show command shows that you have one strict
> > priority queue, that will
> > be (i think but needs confirmation) treated as
> > Conversation 264 on the
> > ouptut scheduler and that this particular queue is
> > policed at 1Mbps and will
> > bc at 25K bytes, therefore the Tc for the priority
> > queue is 200ms.
> >
> > HTH
> >
> > Simon
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com
> > [mailto:nobody@groupstudy.com]On Behalf Of
> > steve.skinner@uk.pwc.com
> > Sent: 08 April 2005 11:36
> > To: ccielab@groupstudy.com
> > Subject: priority command in MDQ
> >
> >
> > guys .
> >
> > i have this config
> >
> > i am trying to understand the prioirty command
> > within the class .
> >
> > according to my understading ,the prioity command
> > sets a Strict Priority
> > per class in the policy .
> >
> > but as i thought you would usually only have 1 type
> > of traffic per class
> > ,as in this case ,why do i need to prioritise the
> > only traffic type in this
> > class .
> >
> > i have put my most important class at the top of the
> > policy ,so this will
> > get queued first . but other than that i didn`t
> > think i would need to do
> > anything else.
> >
> > TIA
> >
> > steve
> >
> > class-map match-any Steve_VOIP
> > match access-group 90
> > class-map match-any Backup_Servers
> > match access-group 111
> >
> > !
> > policy-map Siemens_Trunk
> > description 1000Kbs Class 1 voice policy
> > class Steve_VOIP
> > police cir 1000000
> > conform-action set-prec-transmit 4
> > exceed-action drop
> > priority 1000
> > class Backup_Servers
> > police cir 250000
> > exceed-action drop
> > class class-default
> > prioity 100
> > set ip precedence 5
> > !
> >
> > output from policy
> >
> > Strict Priority
> > Output Queue: Conversation 264
> > Bandwidth 1000 (kbps) Burst 25000 (Bytes)
> >
> >
> >
> >
> _________________________________________________________________
> > --------------------- End of message text
> > --------------------
> >
> > UK M&A deal confidence survey 2005
> > http://www.pwc.com/uk/dealconfidencesurvey
> >
> >
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