Re: Layer 2 QOS COS marking on Inbound

You can mark and queue on the same interface or same router. Your marks will be in place on the other side of the ptp.

Sent from handheld

On Jul 19, 2011, at 7:35 AM, "Irfan Sid" <lifeoverip_at_gmail.com> wrote:

> 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
>
> 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.
>
> On Mon, Jul 18, 2011 at 6:37 PM, Diment, Andrew <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]
>> 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] 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?
>>>>
>>>>
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>>>>
>>>>
>>>>
>>>>
>>>
>>> --
>>> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>>>
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>> --
>> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>>
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Received on Tue Jul 19 2011 - 11:48:40 ART