From: paul cosgrove (paul.cosgrove@gmail.com)
Date: Tue Dec 16 2008 - 07:25:47 ARST
Hi Pavel,
Judging from the docs the functionality of max-reserved-bandwidth changed
quite a lot in recent releases - as of 12.2(20)T is is no longer supported.
http://ciscosystems.com/en/US/docs/ios/qos/command/reference/qos_m1.html#wp1037779
This release introduced HFQ and standardised QoS behaviour across the
platforms. Incidentaly it also seems to have removed fast switching.
There is a good document on the cisco site which explains the recent QoS
changes. It was written about the service provider track but references
12.4T where the changes seem to have been introduced a little later.
http://www.cisco.com/en/US/technologies/tk543/tk545/technologies_white_paper0900aecd8012032d.html
The following is an extract from the doc:-
Max-Reserved-Bandwidth
Old Behavior
The default maximum reserved bandwidth is 75 percent, so the maximum
bandwidth that can be guaranteed to any user-defined class is also 75
percent. If 75 percent of the bandwidth is allocated only for the LLQ, then
no minimum bandwidth can be guaranteed to the other classes, and they will
share the remaining 25 percent bandwidth with the class default traffic.
If more bandwidth needs to be allocated, use the
max-reserved-bandwidthcommand to modify the bandwidth amount that can
be reserved for user-defined
classes.
New Behavior
The max-reserved-bandwidth command no longer affects the amount of
bandwidth available to a service-policy. 1% must be reserved for the
class-default with the rest being available to the users classes. Please
also refer to the previous section "Allocation of Bandwidth to Class
Default.
Paul.
On Mon, Dec 8, 2008 at 10:01 AM, Pavel Bykov <slidersv@gmail.com> wrote:
> Thanks.
> Functionality of max-reserved-bandwidth did change with latest IOS, but not
> by much.
> You can see this in part 6 of tests on page 22 where testing was done with
> an old IOS. There R2 and R3 which were in class-default should have gotten
> at least something, because the command was set at "max-reserved-bandwidth
> 75", but they didn't and what they got was below 1%.
>
>
> On Sun, Dec 7, 2008 at 1:05 PM, <mihai.grigore@onlinehome.de> wrote:
>
> > Pavel,
> >
> > I started all this from a statement written some time ago. This might
> have
> > been
> > true at the time of writing Doyle's book. In the meantime, Cisco has
> > apparently
> > changed how class-default works and that statement appears to be no
> longer
> > valid.
> >
> > Thank you for your tests and clarifications, you did a great job with
> your
> > tests!
> > I read the pdf that you put on your server. Very thorough testing!!!
> > Basically you conclusion is that max-reserved-bandwidth command is kind
> of
> > useless.
> >
> > It looks like indeed that Cisco has changed the way how
> > max-reserved-bandwidth
> > command works and it will take some time to update the documentation, as
> > usual.
> >
> > Many thanks again for your tests!
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
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> >
> >
> >
> >
> >
> >
> >
> >
>
>
> --
> Pavel Bykov
> ----------------
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>
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