Dot1P-To-Exp Mappings; Exp-To-Dot1P Mappings - Extreme Networks BlackDiamond 6800 MPLS Installation And User Manual

Configuring the MPLS Module
Two mappings are supported:
• dot1p-to-exp
• exp-to-dot1p

Dot1p-to-exp Mappings

The dot1p-to-exp mappings are used by the ingress LSR. When a non-MPLS ingress
frame arrives at the MPLS module, the frame always contains an IEEE 802.1p priority
field.
The value of the priority field is set based on the QoS classification performed by the
ingress I/O module. The ingress I/O modules assign each packet to a hardware queue,
based on the configured ExtremeWare QoS policies. There is a one-to-one mapping
between the hardware queue and the 802.1p priority values that are inserted into
frames forwarded to the MPLS module. For example, the 802.1p priority value is set to
0 for frames forwarded from hardware queue 0, set to 1 for frames forwarded from
hardware queue 1, and so on.
The dot1p-to-exp table maps 802.1 priority values to MPLS EXP values. The table is
completely flexible, such that any 802.1p priority can be mapped to any
<input_value>
EXP . The EXP output_value is set in the MPLS header of the packet as
<output_value>
it is forwarded to the MPLS network.

Exp-to-dot1p Mappings

The exp-to-dot1p mappings are used when the switch performs label swapping as an
intermediate LSR and when the switch is the egress LSR. In both of these cases, the
MPLS module receives an MPLS-encapsulated frame.
The EXP field in the frame is used as an to the exp-to-dot1p table. The
<input_value>
corresponding is an 802.1p priority value. The 802.1p priority value is
<output_value>
inserted into the frame before the frame is forwarded by the MPLS module.
The exp-to-dot1p table is completely flexible, such that any EXP can be
<input_value>
mapped to any 802.1p priority .
<output_value>
The exp-to-dot1p table is also used by Packet over SONET (PoS) ports when classifying
MPLS-encapsulated packets received from the SONET link. When a PoS port receives
an MPLS-encapsulated packet from the SONET link, the packet is classified based on
the EXP value in the MPLS shim header. The EXP value from the received frame is used
as an index into the exp-to-dot1p mapping table to retrieve and 802.1p priority value.
3-18 MPLS Module Installation and User Guide