Configuration Example For Dscp And Pfc Priorities - Dell S6100 Configuration Manual

Dell Networking OS Releases 9.3(0.0) and earlier provide CLI support to specify the priorities for which PFC is enabled on each port. This
feature is applicable only for the tagged packets based on the incoming packet Dot1p and Dot1p based queue classification. This document
will discuss the configurations required to support PFC for untagged packets based on incoming packet DSCP.
For the tagged packets, Queue is selected based on the incoming Packet Dot1p. When PFC frames for a specific priority is received from
the peer switch, the queue corresponding to that Dot1p is halted from scheduling on that port, thus honoring the PFC from the peer. If a
queue is congested due to packets with a specific Dot1p and PFC is enabled for that Dot1p, switch will transit out PFC frames for that
Dot1p. The packet Dot1p to Queue mapping for classification on the ingress must be same as the mapping of Dot1p to the Queue to be
halted on the egress used for PFC honoring. Dell Networking OS ensures that these mappings are identical. This section discusses the Dell
Networking OS configurations needed for above PFC generation and honoring mechanism to work for the untagged packets.
PRIORITY to PG mapping (PRIO2PG) is on the ingress for each port. By default, all priorities are mapped to PG7. A priority for which PFC
has to be generated is assigned to a PG other than PG7 (say PG6) and buffer watermark is set on PG6 so as to generate PFC.
In ingress, the buffers are accounted at per PG basis and would indicate the number of the packets that has ingress this port PG but still
queued up in egress pipeline. However, there is no direct mapping between the PG and Queue.
Packet is assigned an internal priority on the ingress pipeline based on the queue to which it is destined. This Internal-priority to Queue
mapping has been modified and enhanced as follows for the device:
Table 17. Priority to Queue Mapping
Dot1p 0
Priority
Queue 1
Default dot1p to queue configuration is as follows:

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
Expected PFC 1
Priority
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.
Dell(conf)#do show qos dot1p-queue-mapping
Dot1p Priority : 0
Queue : 1
3 Dot1p->Queue Mapping Configuration is retained at the default value.
4 Interface Configurations on server connected ports.
a Enable DCB globally.
Dell(conf)#dcb enable
248 Data Center Bridging (DCB)
1 2
0 2
20 – 25, 30 – 35
2
1 2 3 4 5 6
0 2 3 4 5 6
3 4
3 4
7
7
5 6
5 6
7
7