Re: DSCP AF class

Off hand that sounds good. Just go under the class configuration inside a
policy map and type "?"

Good luck :)

On Tue, Apr 21, 2009 at 9:17 PM, Jay Pal <jay.b.pal_at_gmail.com> wrote:

> Bryan and Ravi,
> Thanks for the explanation. much more comfortable now. this is why I
> love
> this groupstudy forum.
>
> One more question before i get back to my lab work. What are other things
> that can influence a particular queue (LLQ, bandwidth command per class,
> changing the drop value on RED/WRED per class/DSCP, policier)?
>
> thanks
> Jay
>
> On Wed, Apr 22, 2009 at 10:56 AM, Ravi Singh <way2ccie_at_googlemail.com
> >wrote:
>
> > Hi Jay,
> >
> > AF4 does not "have" a better queuing treatment than AF1. It "should" ,
> > as per the defined AF PHB.As WorkerBee said "following the standards
> > help to improve the QoS treatment of properly marked DSCP packets ".So
> > in a live environment, you may want to prefer AF4 over AF1 markings
> > but If you are working in a lab with two routers and you have incoming
> > packets marked as DSCP AF4x and AF1x, there is no default preference
> > of the queuing treatment they will get, since they are both classified
> > into different classes and packets in different classes , for example
> > AF4 and AF1, are processed independently of each other. It's when you
> > explicitly configure a queuing mechanism, as in Bryan's example, that
> > you could affect the preference of one class over another.
> >
> > HTH,
> > Ravi
> >
> > On Wed, Apr 22, 2009 at 3:40 AM, Jay Pal <jay.b.pal_at_gmail.com> wrote:
> > > Hi Ravi, Gaurav, Bryan and WorkerBee,
> > > thanks for the inputs/explaination.
> > > This is where it gets confusing to me. The Qos book (mentioned earlier
> in
> > > the post by Ravi) that 'there is no inherent advantage to being in
> class
> > 4
> > > versus class 1'. And in another post Ravi mentions that
> > > 'For example,
> > > packets in class AF4 should be given better queuing treatment than
> > > packets in AF1.In other words, when you classify and mark packets and
> > > assign them the AF PHB, a packet with a PHB of AF4 is not bound to
> > > receive better queuing treatment than the AF1 packet.'
> > > So I am confused as to why AF4 has better queue treatment than AF1 in a
> > DSCP
> > > aware network. I can understand that if the network is not DSCP aware
> > then
> > > it would give better treatment for AF4 than AF1 (e.g. when you just
> have
> > > WFQ on the interface). I have read few materials on the web and an RFC
> > but
> > > it still not quite clear.
> > >
> > > Bryan, Just to put another requirement on this scenario, lets just say
> > that
> > > you already have LLQ with voice running on EF. You could probably use
> CS
> > 4
> > > and CS1 to achieve this but i am trying to see if there is any other
> way
> > of
> > > doing it by using AF41 and AF11.
> > >
> > > thanks
> > > Jay
> > >
> > > On Wed, Apr 22, 2009 at 10:01 AM, Ravi Singh <way2ccie_at_googlemail.com>
> > > wrote:
> > >>
> > >> Exactly, That's why I said if you have a network domain totally under
> > >> your control you may fiddle with the markings. Forgot to add that
> > >> obviously such non-standard markings will not be of much use when sent
> > >> outside the domain to other DSCP compliant networks. Thanks for adding
> > >> this up WorkerBee.
> > >>
> > >> Regards,
> > >> Ravi
> > >>
> > >> On Wed, Apr 22, 2009 at 2:42 AM, WorkerBee <ciscobee_at_gmail.com>
> wrote:
> > >> > Ravi/Jay,
> > >> >
> > >> > AF classification is meant to standardize QoS service offering. It
> is
> > >> > well understood that EF class is known to every engineer that it
> meant
> > >> > LLQ/Priority while Best Effort is DSCP 0 marking.
> > >> >
> > >> > Of course you can choose to reverse the logic and implement the
> other
> > >> > way round but you won't be integrating very well with other DSCP
> > >> > compliant networks.
> > >> >
> > >> > That's why, you don't have the luxury of control the entire domain
> > >> > but following the standards help to improve the QoS treatment of
> > >> > properly marked DSCP packets.
> > >> >
> > >> > Engineering is fun. :)
> > >> >
> > >> > On Wed, Apr 22, 2009 at 9:27 AM, Ravi Singh <
> way2ccie_at_googlemail.com>
> > >> > wrote:
> > >> >> Hi Jay,
> > >> >>
> > >> >> As per my understanding, while inherently there is no advantage of
> a
> > >> >> packet in one class over a packet in another, the AF PHB states
> that
> > >> >> packets with a higher value of the AF class should be given queuing
> > >> >> preference over packets in a lower value AF class . For example,
> > >> >> packets in class AF4 should be given better queuing treatment than
> > >> >> packets in AF1.In other words, when you classify and mark packets
> and
> > >> >> assign them the AF PHB, a packet with a PHB of AF4 is not bound to
> > >> >> receive better queuing treatment than the AF1 packet. It is totally
> > >> >> upto you on what queuing treatment to give packets in different AF
> > >> >> classes . If you have a network domain totally under your control,
> > you
> > >> >> may wish to provide packets in the AF1 class to be given the best
> > >> >> treatment,whatsoever.
> > >> >>
> > >> >> And while I am writing this, Bryan has already responded on how you
> > >> >> could achieve this configuration. Thanks Bryan.
> > >> >>
> > >> >> Regards,
> > >> >> Ravi
> > >> >>
> > >> >>
> > >> >> On Tue, Apr 21, 2009 at 11:40 PM, Jay Pal <jay.b.pal_at_gmail.com>
> > wrote:
> > >> >>> Hi Ravi,
> > >> >>> In this case I have the same understanding then 'all AF class have
> > the
> > >> >>> same
> > >> >>> priority'.
> > >> >>>
> > >> >>> Is there anyway to make AF4 with higher priority than AF1?
> > >> >>>
> > >> >>> thanks
> > >> >>> Jay
> > >> >>>
> > >> >>> On Tue, Apr 21, 2009 at 11:32 PM, Ravi Singh <
> > way2ccie_at_googlemail.com>
> > >> >>> wrote:
> > >> >>>>
> > >> >>>> Hi Jay,
> > >> >>>>
> > >> >>>> Below is a paste of some relevant lines from the Cisco QoS Exam
> > Cert
> > >> >>>> Guide which will make this clear
> > >> >>>>
> > >> >>>> "An individual PHB describes what happens in a single hop, most
> > >> >>>> typically a router. In the case of AF,
> > >> >>>> each PHB contains two separate QoS function, typically performed
> by
> > >> >>>> two different QoS tools. The
> > >> >>>> first function is queuing. Each router classifies the packets
> into
> > >> >>>> four different classes, and packets
> > >> >>>> from each class are placed in a separate queue.
> > >> >>>>
> > >> >>>> The AF PHB defines Congestion Avoidance as the second behavior
> that
> > >> >>>> comprises the AF PHB.
> > >> >>>>
> > >> >>>> Unlike the CS PHB, AF does not follow the bigger-is- better
> > >> >>>> logic for the AF DSCPs. First, AF11, AF12, and so on are names
> for
> > >> >>>> DSCP values, not the binary
> > >> >>>> of decimal equivalent. Given the names, at least you can
> > >> >>>> think of the first digit after the AF to be the queuing
> > >> >>>> classification for example, all AF4x code
> > >> >>>> points are in the same class for queuing. No specific queuing
> > >> >>>> parameters are implied for any of these
> > >> >>>> classes, so there is no inherent advantage to being in class 4
> > versus
> > >> >>>> class 1.
> > >> >>>>
> > >> >>>> Similarly, the second numeric digit in the AF DSCP names imply
> the
> > >> >>>> drop preference with
> > >> >>>> 3 meaning highest likelihood of being dropped, and 1 meaning the
> > >> >>>> least
> > >> >>>> likelihood. In other words,
> > >> >>>> inside a single class, an AFx3 DSCP would mean that these packets
> > >> >>>> would be dropped more quickly
> > >> >>>> (more aggressively) than AFx2, which would be dropped more
> > >> >>>> aggressively than AFx1 packets. In
> > >> >>>> the actual DSCP names, a bigger number for the second numeric
> digit
> > >> >>>> actually implies a less desirable
> > >> >>>> QoS behavior.
> > >> >>>>
> > >> >>>> HTH,
> > >> >>>> Ravi
> > >> >>>>
> > >> >>>>
> > >> >>>> On Tue, Apr 21, 2009 at 2:23 PM, Jay Pal <jay.b.pal_at_gmail.com>
> > wrote:
> > >> >>>> > ok. I am clear on the drop probability. what about the first
> > >> >>>> > numerical
> > >> >>>> > value. Does AF4 have preference over AF1?
> > >> >>>> >
> > >> >>>> > On Tue, Apr 21, 2009 at 9:19 PM, GAURAV MADAN
> > >> >>>> > <gauravmadan1177_at_gmail.com>wrote:
> > >> >>>> >
> > >> >>>> >> correct !
> > >> >>>> >>
> > >> >>>> >> first integer is "class selector" and second is " drop
> > precedence"
> > >> >>>> >>
> > >> >>>> >> for drop prec : 1,2,3 .... 1 means low 2 means medium and 3
> > means
> > >> >>>> >> high
> > >> >>>> >>
> > >> >>>> >> HTH
> > >> >>>> >> Gaurav Madan
> > >> >>>> >>
> > >> >>>> >> On Tue, Apr 21, 2009 at 6:43 PM, Jay Pal <jay.b.pal_at_gmail.com
> >
> > >> >>>> >> wrote:
> > >> >>>> >>
> > >> >>>> >>> Actually, drop preference is the second numeric value in a
> > >> >>>> >>> particular
> > >> >>>> >>> class
> > >> >>>> >>> like AF11 (low drop), AF12 (medium drop) and AF13 (high
> drop).
> > >> >>>> >>>
> > >> >>>> >>> I was talking more on AF class (AF1, AF2, AF3 and AF4).
> > >> >>>> >>>
> > >> >>>> >>> On Tue, Apr 21, 2009 at 9:07 PM, Divin Mathew John
> > >> >>>> >>> <divinjohn_at_gmail.com
> > >> >>>> >>> >wrote:
> > >> >>>> >>>
> > >> >>>> >>> > AF1, AF2 etc... 1,2 is the drop preference. like AF1 will
> be
> > >> >>>> >>> > dropped
> > >> >>>> >>> > less than AF2 and all
> > >> >>>> >>> > Thanking You
> > >> >>>> >>> >
> > >> >>>> >>> > Yours Sincerely
> > >> >>>> >>> >
> > >> >>>> >>> > Divin Mathew John
> > >> >>>> >>> > divinjohn_at_gmail.com
> > >> >>>> >>> > divin_at_dide3d.com
> > >> >>>> >>> > http://www.dide3d.com
> > >> >>>> >>> > +91 9945430983
> > >> >>>> >>> > +91 9846697191
> > >> >>>> >>> > +974 5008916
> > >> >>>> >>> > PGP PUBLIC KEY BLOCK @
> > >> >>>> >>> > http://www.dide3d.com/divin_Public_PGP_key.txt
> > >> >>>> >>> > Sent from Bangalore, KA, India
> > >> >>>> >>> >
> > >> >>>> >>> >
> > >> >>>> >>> > On Tue, Apr 21, 2009 at 6:31 PM, Jay Pal <
> > jay.b.pal_at_gmail.com>
> > >> >>>> >>> > wrote:
> > >> >>>> >>> > > Hi all,
> > >> >>>> >>> > >
> > >> >>>> >>> > > Just to make sure my understanding is correct on DSCP AF
> > >> >>>> >>> > > class.
> > >> >>>> >>> > > AF1,
> > >> >>>> >>> AF2,
> > >> >>>> >>> > > AF3 and AF4 have the same priority when using DSCP and
> > there
> > >> >>>> >>> > > is
> > >> >>>> >>> > > no
> > >> >>>> >>> > > advantage of using AF4 to AF1 or AF2.
> > >> >>>> >>> > >
> > >> >>>> >>> > > If this is correct is there a way to make one of the AF
> > class
> > >> >>>> >>> > > with
> > >> >>>> >>> more
> > >> >>>> >>> > > priority than other?
> > >> >>>> >>> > >
> > >> >>>> >>> > > thanks
> > >> >>>> >>> > > Jay
> > >> >>>> >>> > >
> > >> >>>> >>> > >
> > >> >>>> >>> > > Blogs and organic groups at http://www.ccie.net
> > >> >>>> >>> > >
> > >> >>>> >>> > >
> > >> >>>> >>>
> > >> >>>> >>>
> > >> >>>> >>>
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-- 
Bryan Bartik
CCIE #23707, CCNP
Sr. Support Engineer - IPexpert, Inc.
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