From the figure below, when a PE router receives a packet with DSCP AF31, it copies the first three bits from the AF31 to the EXP field 3, why the figure from the WAN QoS design guide is showing two EXP fiels instead of one at the egress interface at the PE?
It is a MPLS VPN scenario, therefore there is two labels. The outer label is the IGP label and the inner label is the service label. Each label includes an EXP field, hence two EXP field in this scenario.
Harold Ritter Sr Technical Leader CCIE 4168 (R&S, SP) firstname.lastname@example.org México móvil: +52 1 55 8312 4915 Cisco México Paseo de la Reforma 222 Piso 19 Cuauhtémoc, Juárez Ciudad de México, 06600 México
So which field does the Service Provider use for its own QoS, IGP Label or Inner Label?
Both fields are used during QoS operations.
If inner label wouldn't be marked, imagine at PHP what would happen when topmost label is popped out and inner label is exposed without marking. QoS treatment simply cannot be assured anymore on the FEC.