Users Guide

1542 Class-of-Service
Continuing this example, the egress port te1/0/8 is configured for strict
priority on queue 4, and a weighted scheduling scheme is configured for
queues 3-0. Assuming queue 3 has a higher minimum bandwidth than queue
1 (relative bandwidth values are shown as a percentage, with 0% indicating
the bandwidth is shared according to the default weighting), the queue
service order, when congested, is 4 followed by 3 followed by 1. Assuming each
queue transmits all packets shown in the diagram, the packet transmission
order as seen on the network out of port te1/0/8 is B, D, A, C. Thus, packet B,
with its strict priority scheduling, is transmitted ahead of the other packets at
the egress port.
The following commands configure port 10 (ingress interface) and port 8
(egress interface).
1 Configure the Trust mode for port 10.
console#config
console(config)#interface tengigabitethernet 1/0/10
console(config-if-Te1/0/10)#classofservice trust dot1p
2 For port 10, configure t he 802.1p user priority 7 to send the packet to
queue 4 instead of the default queue (queue 3).
console(config-if-Te1/0/10)#classofservice dot1p-mapping 7 4
3 For port 10, specify that untagged VLAN packets should have a default
priority of 2, which maps to queue 0.
console(config-if-Te1/0/10)#vlan priority 2
console(config-if-Te1/0/10)#exit
4 For port 8, the egress port, configure a weighted scheduling scheme for
queues 3–0.
console(config)#interface tengigabitethernet 1/0/8
console(config-if-Te1/0/8)#cos-queue min-bandwidth 5 5 20 40 0
0 0
5 Configure port 8 to have strict priority on queue 4:
console(config-if-Te1/0/8)#cos-queue strict 4
To configure the CoS queues for lossless traffic when transporting iSCSI
traffic, set the lossless traffic class to have a one-to-one mapping with the
priority value. The following example illustrates how to change the dot1p
mapping from the switch defaults to support lossless
1
transport of frames on
CoS queue 4, with a 50% minimum bandwidth guarantee. Lossless traffic
1. Lossless behavior is guaranteed only when configured in conjunction with a conges-
tion control mechanism such as PFC.