Dell S4048T - Configuration Example for DSCP and PFC Priorities

The packets come in with packet-dot1p 2 alone use Q1 (as per dot1p to Queue classification – Table 2) on
the egress port.
• When Peer sends a PFC message for Priority 2, based on above PRIO2COS table (TABLE 2), Queue 1 is
halted.
• Queue 1 starts buffering the packets with Dot1p 2. This causes PG6 buffer counter to increase on the
ingress, since P-dot1p 2 is mapped to PG6.
• As the PG6 watermark threshold is reached, PFC generats for dot1p 2.
Configuration Example for DSCP and
PFC Priorities
Consider a scenario in which the following DSCP and PFC priorities are necessary:
DSCP
0 – 5, 10 - 15 20 – 25, 30 – 35
Expected PFC
Priority
1 2
To configure the aforementioned DSCP and PFC priority values, perform the following tasks:
1 Create class-maps to group the DSCP subsets
class-map match-any dscp-pfc-1
match ip dscp 0-5,10-15
!
class-map match-any dscp-pfc-2
match ip dscp 20-25,30-35
2 Associate above class-maps to Queues Queue assignment as below.
NOTE: Although, each port on the S4810, S4820T, and S5000 devices support 8 QoS queues, you
can configure only 4 QoS queues (0-3)to manage data traffic. The remaining 4 queues (4-7) are
reserved for control traffic.
Table 20. Queue Assignments
Internal-
priority
0 1 2 3 4 5 6 7
Queue 0 0 0 1 2 3 3 3
3 Dot1p->Queue Mapping Configuration is retained at the default value.
Default dot1p-queue mapping is,
Dell#show qos dot1p-queue-mapping
Dot1p Priority : 0 1 2 3 4 5 6 7
Queue : 0 0 0 1 2 3 3 3
Default dot1p-queue mapping is,
Dell#show qos dot1p-queue-mapping
Dot1p Priority : 0 1 2 3 4 5 6 7
Queue : 2 0 1 3 4 5 6 7
4 Interface Configurations on server connected ports.
Data Center Bridging (DCB) 310