Re: DSCP AF class

Thanks Bryan.

On Wed, Apr 22, 2009 at 11:24 AM, Bryan Bartik <bbartik_at_ipexpert.com> wrote:

> 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.
> URL: http://www.IPexpert.com

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Received on Wed Apr 22 2009 - 11:38:00 ART