Switching QOS.

[ajay chauhan]

Hey Guys,

can someone please explain how internal cos-to-dscp and dscp-to-cos map works ?

https://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_58_se/configuration/guide/swqos.html#wp1157930

lets say a ip phone is connected to access switch and interface is configured as cos trust .In this case cos-to -dscp map will be used on ingress port ,I read somewhere these dscp values are internal/within switch.

If a router is connected to this switch and I want to match EF/46 how does switch mark this packet to use DSCP value ?

how many times maps are used within switch ?

Just trying to understand internal process of qos on switch

Thanks

Ajay

[acampbell]

Ajay,

Have a look at page 7

Figure 37-3 Classification Flowchart

on this link

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_55_se/configuration/guide/swqos.pdf

Regards,
Alex.
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[ajay chauhan]

Thanks for Reply.

I understand this doubt comes if the dscp values genrated by cos-dscp map is internal to switch then how can I match the same on next hop router.

So what would be diffrence between internal dscp and dscp .

Ajay

[cadet alain]

Hi,

the outgoing DSCP value will be 40 due to Cos to DSCP mapping default and so you must either:

-disable DSCP rewrite: no mls qos rewrite ip dscp

- modify Cos to DSCP map: mls qos map cos-dscp

- trust on DSCP: mls qos trust dscp

Regards.

Alain

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