Re: Layer 2 QOS COS marking on Inbound

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