From: Scott Morris (swm@emanon.com)
Date: Tue Sep 24 2002 - 21:39:14 GMT-3
priority
To give priority to a class within a policy map, use the priority
policy-map class configuration command. To disable the strict priority
queue, use the no form of this command.
priority bandwidth
no priority [bandwidth]
Syntax Description bandwidth
Guaranteed allowed bandwidth (in kbps) for the priority traffic. Beyond
the guaranteed bandwidth, the priority traffic will be dropped in the
event of congestion to ensure that the nonpriority traffic is not
starved.
That's an interesting way to interpret the wording, but not really how
it works! Both bandwidth and priority demonstrate how a series of
queues are emptied into an interface. (remember that if no congestion,
no queuing, no problem)
One major difference in how they're handled is what happens when the
upper limit is reached. If you have:
Class voice
priority 128
Class stuff
bandwidth 128
When 128k of class voice is reached, classified packets will get dropped
to not impede other traffic. When 128k of class stuff is reached,
overflow packets are reclassified into class default, which will benefit
from whatever leftover bandwidth there is.
From a queuing scheme, you can allocate 75% of available bandwidth
(changed with the max-allocate-bandwidth command).
In the case of both commands, they are viewed as the maximum guaranteed
bandwidth allowed. Anything in "priority" bandwidth will always get
emptied before anything else does (strict priority), and therefore any
extra is dropped. Anything in other queues will be emptied in a
pseudo-weighted-round-robin fashion based on the configrations, and any
overflow traffic is dropped into the "default" queue. If the default
queue overflows then traffic is dropped.
Also, when you use priority, the amount of guaranteed bandwidth is taken
out of the available pool. This means if you have a 10 meg link, and
guarantee 2000 to a priority queue, that means that 8000k is available
for other queues. Of that, 75% of the 8000k is available by default for
allocation.
Hope that helps!
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
stephen.paynter@bt.com
Sent: Tuesday, September 24, 2002 11:33 AM
To: elpingu@acedsl.com; adam.crisp@totalise.co.uk
Cc: ccielab@groupstudy.com
Subject: RE: CB WFQ
if you want to divide equally use the priority keyword instead of
bandwidth percent 50.
ie on ethernet priority 5000
if you use bandwidth percent that is classed as minimum, priority is
classed as maximum
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/
qos_r/qrdcmd3.htm#1036072
Stephen Paynter CCIE #10206
Customer Engineer
BT Ignite- Customer Engineering Unit, National Solutions
T: +44 (0)1422 338881 F: +44 (0)1422 316637 M: +44 (0)7974 087949
e-mail: stephen.paynter@bt.com
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-----Original Message-----
From: elping [mailto:elpingu@acedsl.com]
Sent: 24 September 2002 03:18
To: Adam Crisp
Cc: Ccielab
Subject: Re: CB WFQ
my friend
CB-WFQ will not do the trick
i though the same thing a while back ...here is the scoop on CB-WFQ.
this method will only gurantee the allocated bandwithd during congestion
.
now the question says ..
dived traffic exactly .....then CB-WFQ will not do the trick..
try custom queeing ..or CAR
Elping
.
Adam Crisp wrote:
> Hi,
>
> If asked to divide up bandwidth EXACTLY, can I use CB-WFQ, with the
> "bandwidth percent XX" command?
>
> eg
>
> class-map match-all my_class_queue_ip
> match access-group 25
> !
> policy-map my_policy
> class my_class_queue_ip
> bandwidth percent 50
>
> OR does this call for Custom Queuing?
>
> thanks in advance...
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