From: simon hart (simon.hart@btinternet.com)
Date: Sat Apr 09 2005 - 05:20:42 GMT-3
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)
>
>
>
>
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