Hello QOS Guru,
I am trying to set up qos and would like some clarification on the "cos-to-dscp" and "dscp-to-cos" mapping to ensure my understanding is correct.
Here is my scenario:
cisco phone --- f0/1-(3560sw)-gig0/1-----trunk 802.1q----- gig0/2-(3750sw)-gig0/1------gig01-(Service provider Router).
I understand cisco phone will send both cos5 and dscp 46 markings by default, so on the 3560 sw port f0/1 i have elected to use the " mls qos trust cost " command to trust cos instead of dscp. The "mls qos trust cos" command will now tricker the 3560sw to use the internally mapping cos-to-dscp and this will ( Show mls qos map gives me cos-dscp 0 8 16 24 32 46 48 56) convert the cos value to dscp 46 when egress out the 3560 gig0/1 to the uplink 3750sw gig0/2. The below part is where i am at a lost ........
On the 3750 gig0/2 ingress port, do i use the mls qos trust dscp at this point? My concern is if i use the "trust dscp" the 3750 sw will convert the marking from dscp to cos due to the internally mapping on the 3750sw and on egress gig0/1 the service provider will get a cos value instead of a dscp value? or maybe not, since it isn't a trunk link between the 3750sw and the SP router?
I understand the Service Provider would want dscp and not cos value.