mls qos queueing-only mode

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Jan 19th, 2009
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Hi,

I was reading the mls qos and found that

When you enable queueing-only mode, the switch does the following:


•Disables marking and policing globally


•Configures all ports to trust Layer 2 CoS




Note The switch applies the port CoS value to untagged ingress traffic and to traffic that is received through ports that cannot be configured to trust CoS.


Now my question is, if i have incomming traffic pure IP with dscp bit and MPLS traffic with toplable with EXP on switch. Will mls qos queueing-only mode will assing Cos internally for above untagged traffic ? if so, how does mapping happen from dscp to cos and exp to cos internally so that on egress i assging those internal cos to queue and threshold for WRR.


Regards,

Chintan

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Giuseppe Larosa Tue, 01/20/2009 - 02:57
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Hello Chintan,


just one note:

internally a switch uses internal DSCP tags not CoS tags for implementing QoS.


Then queueing on physical ports uses CoS after DSCP to CoS mappings


on input ports the internal DSCP settings can come from trusting the port traffic or other options


Hope to help

Giuseppe


chintan-shah Tue, 01/20/2009 - 06:53
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Hi Giuseppe,


In our scenario, Incomming traffic is without any VLAN tagging on L2 port of switch and we have those input ports on switch configure with access vlans. egress port from switch to uplink is 802.1Q.


So problem is i can't do Qos with trust cos , i have traffic either IPv4 +MPLS both. so how does mls qos queining-only mode will help me to assing dscp to cos and exp to cos for incomming traffic and do egress qos based on that Cos value ??


Regards,

Chintan

Giuseppe Larosa Tue, 01/20/2009 - 09:29
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Hello Chintan,

what platform is the L2 switch and IOS version I didn't find the command in command reference of C3750 and C4500.

Or if you have a link to the documentation you are using.



I see that the scenario is a challenge for a L2 switch.

IPv4 traffic could be handled by trusting DSCP but for MPLS EXP I have doubts too.


Hope to help

Giuseppe


chintan-shah Tue, 01/20/2009 - 21:36
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Hi Giuseppe,


I will be using 6500 - Sup720-10G with 12.2(33)SXI.

I see the command "mls qos mpls trust" but i can't have both dscp and mpls trust command on same interface so i understood that using mls qos queing only, i can map incomming dscp/exp to cos even ingress port trffic not tagged...


Any idea ??


Regards,

Chintan


mlund Wed, 01/21/2009 - 01:05
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Hi Chintan

I'm not sure about queing only mode, but if you trust dscp, Layer3 mpls-tagged packet will be trusted by default.


/Mikael

chintan-shah Wed, 01/21/2009 - 01:24
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Hi Mikael,


Do you mean if i have mls qos trust dscp , and if incommingpacket have MPLS lable it will trust EXP ???


REgards,

Chintan

mlund Wed, 01/21/2009 - 01:53
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Hi


Yes, that's right


/Mikael

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