Re: Layer 2 QOS COS marking on Inbound

On routers you usually use DSCP, not COS. Remember that you don't have
COS unless you have 802.1q or .1p

All involved hops need to agree on some kind of behaviour for the system
to work. It would be easier to have one standard marking scheme, but
every designer has a different view of what it should be :)
Cisco has some proposals... but in general, remarking at the edges is
needed.

-Carlos

Irfan Sid @ 19/07/2011 08:48 -0300 dixit:
> Thanks for your patience with me, as QoS is a new but interesting topic
> for me :)
> Can you classify and then define your own Cos and DSCP values and give
> them treatment as you wish, or do you have to follow the DSCP and
> COS industry defined standards? Can you assume the DSCP/COS values are
> just a community value which you set and then match for treatment, or
> are they more then that, in which case I should use the values carefully.
> On Tue, Jul 19, 2011 at 2:42 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar
> <mailto:tron_at_huapi.ba.ar>> wrote:
>
> Irfan Sid @ 19/07/2011 08:31 -0300 dixit:
>
> Is it possible to classify and mark traffic on inbound LAN
> interface of a Router and then queue and shape the marked
> traffic on the outbound WAN interface of the 'same' Router? Or
> does classification and marking have to be done before it enters
> the router
>
>
> Yes, you can classify + mark on ingress and shape on egress.
>
>
> Also if its point to point WAN link will the other end get the
> Qos Marking as well, so I can do Policing based on the same marking.
>
>
> Of course you can. This is the whole point of differenciated services!
> -Carlos
>
>
> On Mon, Jul 18, 2011 at 6:37 PM, Diment, Andrew
> <Andrew.Diment_at_qwest.com <mailto:Andrew.Diment_at_qwest.com>
> <mailto:Andrew.Diment_at_qwest.__com
> <mailto:Andrew.Diment_at_qwest.com>>> wrote:
>
> Here's 3 lines I got out of the doc you sent. But I do think you
> are also correct and it relates to the hardware platform. 3750
> thresholds and what queues the traffic goes into for inbound and
> outbound traffic can be determined by COS or DSCP. Some 6500
> blades
> only use COS and some can do both. Very confusing!!!
>
> 1) The switch uses the internal DSCP value to generate a CoS
> value
> representing the priority of the traffic.
>
> 2) If you configure a port with either of these options and
> non-IP
> traffic is received, the switch assigns a CoS value and
> generates an
> internal DSCP value from the CoS-to-DSCP map. The switch uses the
> internal DSCP value to generate a CoS value representing the
> priority of the traffic.
>
> 3) Regardless of the DSCP transparency configuration, the switch
> modifies the internal DSCP value of the packet, which the switch
> uses to generate a class of service (CoS) value that
> represents the
> priority of the traffic
>
>
>
> -----Original Message-----
> From: Carlos G Mendioroz [mailto:tron_at_huapi.ba.ar
> <mailto:tron_at_huapi.ba.ar>
> <mailto:tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>]
> Sent: Monday, July 18, 2011 10:03 AM
> To: Diment, Andrew
> Cc: Irfan Sid; Cisco certification
> Subject: Re: Layer 2 QOS COS marking on Inbound
>
> Hmm,
> I have seen many documents talking about "internal DSCP" and
> how the
> maps go from COS to DSCP (input) to COS again (output).
>
> Actually, you may use COS or DSCP on input (via trust) and
> not remark
> the DSCP.
>
> Take a look at table 31-3 on
>
> http://www.cisco.com/en/US/__partner/docs/switches/lan/__catalyst2960/software/release/__12.2_46_se/configuration/__guide/swqos.html
> <http://www.cisco.com/en/US/partner/docs/switches/lan/catalyst2960/software/release/12.2_46_se/configuration/guide/swqos.html>
>
> -Carlos
>
> Diment, Andrew @ 18/07/2011 10:52 -0300 dixit:
> > Actually you have that a little backwards, switches use COS
> internally. What that internal COS value is set to depends
> on what
> is "trusted" on the interface. If you trust COS (mls qos
> trust cos)
> it will use the COS value in the 802.1p field of the incoming
> packet
> AND will change the DSCP value using the COS-to-DSCP table.
> Thatb s
> why for VoIP traffic you always have to adjust the table with the
> command "mls qos map cosb dscp 0 8 16 24 32 46 48 56"
> because the
> standard says to use DSCP 40 for COS 5 but VoIP uses DSCP 46
> and we
> don't want that overwritten to 40.
> >
> > If it's the native vlan (no 802.1p tag) or the link is not a
> trunk the COS value and DSCP value will both be set to zero,
> which
> is the default and configurable. You can turn this rewriting off
> also if you wish. If the interface has "mls qos trust dscp"
> configured it will use the dscp-to-COS table to determine the
> internal COS value.
> >
> > This doc has a very good explanation.
> >
> >
>
> http://www.cisco.com/en/US/__products/hw/switches/ps5023/__products_tech___note09186a0080883f9e.shtml
> <http://www.cisco.com/en/US/products/hw/switches/ps5023/products_tech_note09186a0080883f9e.shtml>
> >
> >
> > Andy
> > CCIE 10685
> >
> >
> > -----Original Message-----
> > From: nobody_at_groupstudy.com <mailto:nobody_at_groupstudy.com>
> <mailto:nobody_at_groupstudy.com <mailto:nobody_at_groupstudy.com>>
> [mailto:nobody_at_groupstudy.com <mailto:nobody_at_groupstudy.com>
> <mailto:nobody_at_groupstudy.com <mailto:nobody_at_groupstudy.com>>__] On
>
> Behalf Of Carlos G Mendioroz
> > Sent: Monday, July 18, 2011 4:37 AM
> > To: Irfan Sid
> > Cc: Cisco certification
> > Subject: Re: Layer 2 QOS COS marking on Inbound
> >
> > COS is not carried from input to output, but instead,
> converted to
> > internal DSCP using cos-to-dscp if cos is trusted on input or
> > override is used.
> >
> > On output, its value is mapped using dscp-to-cos and set
> on the
> egress
> > frame if the frame supports it.
> > DSCP is also reset unless pass through is used, or modified by
> some exit
> > policy.
> >
> > But make yourself a favour and test it. That's the best way to
> learn it!
> >
> > -Carlos
> >
> > Irfan Sid @ 18/07/2011 01:58 -0300 dixit:
> >> Hi Group.
> >>
> >> On the Cisco switches (2960) can I apply layer 2 COS marking
> inbound on a
> >> Dot1q trunk, or can it be applied outbound only?
> >>
> >> I understand when a Frame comes inbound on a Trunk, the
> Vlan tag
> is removed,
> >> so dot1p cos cannot be applied.
> >>
> >> On the outbound, the VLAN tag is added on a trunk and
> 802.1p COS
> value can
> >> be attached to the frame.
> >>
> >> Is this understand correct.
> >>
> >> However, I have seen mls qos cos <value> override,
> applied on
> voice vlans
> >> on phone ports so not sure if the cos is written to the frame
> and classified
> >> before the vlan tag is removed on the inbound.
> >>
> >> Please can someone correct my understanding?
> >>
> >>
> >> Blogs and organic groups at http://www.ccie.net
> <http://www.ccie.net/>
> <http://www.ccie.net/>
> >>
> >>
>
> ___________________________________________________________________________
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> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >
> > --
> > Carlos G Mendioroz <tron_at_huapi.ba.ar
> <mailto:tron_at_huapi.ba.ar> <mailto:tron_at_huapi.ba.ar
> <mailto:tron_at_huapi.ba.ar>>>
>
> LW7 EQI Argentina
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> <http://www.ccie.net/>
> <http://www.ccie.net/>
> >
> >
>
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> >
> >
> >
> >
> >
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> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar
> <mailto:tron_at_huapi.ba.ar> <mailto:tron_at_huapi.ba.ar
> <mailto:tron_at_huapi.ba.ar>>>
>
> LW7 EQI Argentina
>
> This communication is the property of Qwest and may contain
> confidential or
> privileged information. Unauthorized use of this communication is
> strictly
> prohibited and may be unlawful. If you have received this
> communication
> in error, please immediately notify the sender by reply
> e-mail and
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> all copies of the communication and any attachments.
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> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar <mailto:tron_at_huapi.ba.ar>>
> LW7 EQI Argentina
>
>

-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net