From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Fri Jun 04 2004 - 17:41:29 GMT-3
That simply means that the sum of all non-default classes
reservations cannot exceed 75% of the bandwidth, interface or available
depending on the IOS release. Class-default traffic is not guaranteed
in the case of congestion. The following policies are not the same:
policy-map A
class X
bandwidth percent 75
policy-map B
class X
bandwidth percent 75
class class-default
bandwidth percent 25
Suppose that the output queue is completely full of traffic from
class X. In the first case, policy-map A, class-default traffic will be
tail dropped as it attempts to enter the output queue. It is not
guaranteed admission. In the second case, policy-map B, class-default
traffic will be admitted and class X traffic in excess of 75% may be
dropped.
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987 x 705
Outside US: 775-826-4344 x 705
> -----Original Message-----
> From: Spolidoro, Guilherme [mailto:Guilherme.Spolidoro@unisys.com]
> Sent: Friday, June 04, 2004 3:29 PM
> To: Brian McGahan
> Cc: ccielab@groupstudy.com
> Subject: RE: QoS - Police - Congestion - NoCongestion
>
> I suggest you go back to the link that I sent before:
>
> CBWFQ Bandwidth Allocation
> The sum of all bandwidth allocation on an interface cannot exceed 75
> percent of the total available interface bandwidth. The remaining 25
> percent is used for other overhead, including Layer 2 overhead,
routing
> traffic, and best-effort traffic. Bandwidth for the CBWFQ
class-default
> class, for instance, is taken from the remaining 25 percent.
>
> From:
>
http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configur
at
> ion_guide_chapter09186a00800b75a9.html#1001225
>
>
>
> -----Original Message-----
> From: Brian McGahan [mailto:bmcgahan@internetworkexpert.com]
> Sent: Friday, June 04, 2004 3:58 PM
> To: Spolidoro, Guilherme
> Cc: ccielab@groupstudy.com
> Subject: RE: QoS - Police - Congestion - NoCongestion
>
>
> > Therefore, if the traffic from class-default wants/needs to use bw,
> > there'll always be 25% guaranteed for it
>
> No this is not true. Class-default is best-effort unless you
> manually reserve bandwidth for it. In the case of congestion, traffic
> that falls into the default-class can still be dropped from the output
> queue. Routing traffic is treated differently though. See the
> following document for more information:
>
> http://www.cisco.com/warp/public/105/rtgupdates.html
>
>
> HTH,
>
> Brian McGahan, CCIE #8593
> bmcgahan@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987 x 705
> Outside US: 775-826-4344 x 705
>
>
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > Spolidoro, Guilherme
> > Sent: Friday, June 04, 2004 1:37 PM
> > To: Carlos G Mendioroz; Bob Sinclair
> > Cc: ccielab@groupstudy.com
> > Subject: RE: QoS - Police - Congestion - NoCongestion
> >
> > Carlos, not sure if I understand your question but the class-default
> is
> > always there (implicit) and you cannot reserve more than 75% in all
> other
> > classes combined (unless you use the max-reserved-bandwidth
command).
> > Therefore, if the traffic from class-default wants/needs to use bw,
> > there'll always be 25% guaranteed for it (among other things like
> routing
> > traffic), otherwise class a can use as much as it is available.
> >
> >
> > Bob, I guess we all learn something new everyday, rigth? :-)
> >
> > For some reason I always understood that the exceed/overflow traffic
> from
> > a given class would dispute the remaining of the bw with the
overflow
> of
> > all other classes by using the WFQ algorithm, where packets with
> higher IP
> > Precedence get more bw.
> >
> > Doesn't sound like this is the case. Please visit the following
link:
> >
> >
>
http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configur
> at
> > ion_guide_chapter09186a00800b75a9.html#1009161
> >
> >
> >
> > Thanks.
> >
> >
> >
> >
> > -----Original Message-----
> > From: Carlos G Mendioroz [mailto:tron@huapi.ba.ar]
> > Sent: Friday, June 04, 2004 10:23 AM
> > To: Bob Sinclair
> > Cc: Spolidoro, Guilherme; ccielab@groupstudy.com
> > Subject: Re: QoS - Police - Congestion - NoCongestion
> >
> >
> > Me too. (inter class WFQ that is)
> >
> > I've been told that there is sort of priority to bandwidth assigned
> > classes wrt non bandwidth assigned classes.
> > So if you have class a bw 10% and class-default w/o bw, enough class
a
> > traffic can starve the rest of the link.
> >
> >
> > Bob Sinclair wrote:
> >
> > > Guiherme,
> > >
> > > According to Wendell Odom in his book Cisco DQOS, the CBWFG
> algorithm is
> > not
> > > published. I have a hard time seeing how it could be
> precedence-based,
> > like
> > > WFQ. Do you have a reference you can share?
> > >
> > > Thanks!
> > >
> > > Bob Sinclair
> > > CCIE #10427, CISSP, MCSE
> > > www.netmasterclass.net
> > >
> > >
> > > ----- Original Message -----
> > > From: "Spolidoro, Guilherme" <Guilherme.Spolidoro@unisys.com>
> > > To: <ccielab@groupstudy.com>
> > > Sent: Friday, June 04, 2004 9:32 AM
> > > Subject: RE: QoS - Police - Congestion - NoCongestion
> > >
> > >
> > >
> > >>The word that should be used with CBWFQ is not reserve but
> guarantee.
> > >>
> > >>When you type the bandwidth percent 25 command on the class,
what's
> > gonna
> > >
> > > happen is that CBWFQ will guarantee at least 25% of the bw for
this
> > class
> > > during congestion.
> > >
> > >>If there's no congestion, the bw command will never kick off. It's
> used
> > >
> > > only during congestion, meaning it's basically a technology used
to
> > empty
> > > the queues (when used with the bw statement).
> > >
> > >>If there's enough bw for everyone, there's no reason to guarantee
> > >
> > > anything, right?
> > >
> > >>If this class doesn't need to use 25% or more (let's say it's
using
> only
> > >
> > > 10%), the rest of the classes can use the remaining of the bw (the
> other
> > 15%
> > > that this class doesn't need).
> > >
> > >>CBWFQ uses the WFQ algorithm, meaning that packets from the
> different
> > >
> > > classes that have the highest IP Precedence will be the ones to
> benefit
> > more
> > > from that. Let me give you an example:
> > >
> > >>class a = streaming video (ip prec 4)
> > >>class b = bulk data (ip prec 1)
> > >>class c = voip (ip prec 5)
> > >>class default-class = anything else (ip prec 0)
> > >>
> > >>Class c has 25% of the bw guarantee for it, but might need only
10%
> at a
> > >
> > > given time.
> > >
> > >>Class a has 5% of the bw guarantee for it, but might need more
than
> that
> > >
> > > at a given time.
> > >
> > >>Class b has 5% of the bw guarantee for it, but might need more
than
> that
> > >
> > > at a given time.
> > >
> > >>class default-class has 25% of the bw guarantee for it by default,
> but
> > >
> > > might need more than that at a given time.
> > >
> > >>If there's congestion on the link, class c (voip) will get the 10%
> that
> > it
> > >
> > > needs. Classes a, b and the default-class' overflow will compete
for
> the
> > > remaining bandwidth. They will use at least the bw that is on the
> > command
> > > plus whatever they can get.
> > >
> > >>Class a's overflow will be able to get more bw than class b and
the
> > >
> > > default-class' overflows.
> > >
> > >>By the end, you might see something like this:
> > >>
> > >>Class c only needed 10% and that's what it got.
> > >>Class a ended up getting 35% of the total bw.
> > >>Class b ended up getting 25% of the total bw.
> > >>Class default-class ended up getting 30% of the total bw.
> > >>
> > >>Not sure if this is a good example, but the idea is that all the
> > overflows
> > >
> > > will leave the queue faster or slower according to their IP
> > Precedence...
> > >
> > >>Without making it more confusing than it has to be, there are
other
> > >
> > > options on CBWFQ (besides the bw command):
> > >
> > >>- priority = new version of the low latency queue, typically used
> for
> > voip
> > >
> > > or interactive video. Instead of putting the packets in the queue,
> it
> > sends
> > > directly to the interface (except for the overflow) In our
example,
> you
> > > could it on class c.
> > >
> > >>- policy = new version of the old CAR. Let you limit the traffic
> that
> > the
> > >
> > > class can use either for inbound or outbound. I personally don't
> like it
> > > because the way it works (basically drops the excess) causes too
> many
> > > retransmissions.
> > >
> > >>- shape = new version of the old traffic shape. Let you limit the
> > traffic
> > >
> > > that the class can use for outbound only. I use extensive here and
> it
> > works
> > > very well.
> > >
> > >>I know this address a lot more than what you asked but I hope
others
> on
> > >
> > > the list can benefit from it.
> > >
> > >>
> > >>-----Original Message-----
> > >>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On
Behalf
> Of
> > >>gladston@br.ibm.com
> > >>Sent: Friday, June 04, 2004 8:51 AM
> > >>To: ccielab@groupstudy.com
> > >>Subject: QoS - Police - Congestion - NoCongestion
> > >>
> > >>
> > >>Dear Group,
> > >>
> > >>Does Police within CBWFQ reserve a bandwidth when there is no
> congestion
> > >
> > > and when there is congestion?
> > >
> > >>For example, to reserve 25% of the bandwidth to traffic from
> 10.100.5.0
> > to
> > >
> > > 10.200.6.0:
> > >
> > >>Class-map p-100.5.0
> > >> Match access-group name p-100.5.0
> > >>!
> > >>policy QOS
> > >>class p-100.5.0
> > >>police 10000 1000 conform-action transmit exceed-action drop
> > >>!
> > >>interface ser 1
> > >> service-policy output QOS
> > >>
> > >>
> > >>If so, why should one use bandwidth and policy within the same
> class?
> > >>
> >
>
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> _
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> > >>
> >
>
>>______________________________________________________________________
> _
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> > >
> > >
>
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