Re: Layer 2 QOS COS marking on Inbound

So on a switchpoirt, the Cos value (from a trunk port or voice vlan
port) gets converted to an internal DSCP value which is then propagated as a
DSCP value across the IP network. In the case you have further Dot1

On Tue, Jul 19, 2011 at 3:06 PM, Carlos G Mendioroz <tron_at_huapi.ba.ar>wrote:

> 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<Andrew.Diment_at_qwest.com>
>> >
>> <mailto:Andrew.Diment_at_qwest.__**com
>> <mailto:Andrew.Diment_at_qwest.**com <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>
>> <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>
>> <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
>> >
>> >
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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
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>> privileged information. Unauthorized use of this communication
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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

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Received on Tue Jul 19 2011 - 15:15:43 ART