Ingress Traffic Processing
Qumran can process packets based on the priority information of the packet. During the packet processing, there are several opportunities to influence the processing by the following configurations:
1. Derive internal priority and drop precedence from the packets IEEE 802.1p (PCP) value and drop eligibility indicator (DEI) value. The Priority Code Point (PCP) is a 3-bit field within an 802.1Q tagged frame that is used to convey the internal priority of the frame and DEI is a single bit that is used to convey the drop precedence of the frame.
Note: The PCP field was formerly called 802.1p.
2. Derive internal priority and drop precedence from the packets DSCP value.
3. Force modification of internal priority and drop precedence using user defined ingress mapping profile.
4. Force the internal priority value based on classification configured using policy maps. This is used for setting a specific priority for L2, L3 or L4 traffic flow.
5. Packet priority and drop precedence will be based on PCP and DEI values for the traffic received on switch ports. Similarly, packet priority and drop precedence will be based on DSCP value for the IPv4 traffic received router ports. For MPLS traffic on label switched interface, packet priority is based on topmost label's EXP value.
6. When trust level on switch ports is modified to trust DSCP values, packet priority and drop precedence for IPv4 traffic will be based on DSCP value.
7. Assign internal priority to untagged traffic on switch port with port level untagged priority configuration.
Mapping Inbound Packet Priorities to Internal Priorities
Priority and drop precedence information is collected from various portions of the packet header:
• If a tagged packet is received on a switch port, derive a priority value from PCP and drop precedence DEI value.
• If a tagged packet is received on a switch port on which trust level is set to DSCP, derive the priority value from DSCP bits. Drop precedence will be derived from DEI bit value.
• If an untagged packet is received on a switch port, assign priority value based on port level untagged priority configuration.
• If an untagged packet is received on a switch port on which trust level is set to DSCP, derive the drop precedence value from DSCP bits.
• If IPv4 packet is received on a router port, derive a priority value and drop precedence by decoding the DSCP bits.
• If MPLS packet is received on a label switched port, derive a priority value and drop precedence by decoding EXP bits.
• The derived values for PCP and DSCP are mapped to a default map.