Chapter 26 Configuring Qos - Cisco Catalyst 3750 Software Configuration Manual

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C H A P T E R
Configuring QoS
This chapter describes how to use different methods to configure quality of service (QoS) on the
Catalyst 3750 Metro switch. With QoS, you can provide preferential treatment to certain traffic at the
expense of others. Without QoS, the switch offers best-effort service to each packet, regardless of the
packet contents or size. It sends the packets without any assurance of reliability, delay bounds, or
throughput.
You can use auto-QoS to identify ports connected to Cisco IP phones and ports that receive trusted voice
over IP (VoIP) traffic.
You can use standard QoS to classify, police, mark, queue, and schedule inbound traffic on any port as
well as queue and schedule outbound traffic. On ingress, standard QoS offers classification based on the
class of service (CoS), Differentiated Services Code Point (DSCP), or IP precedence value in the
inbound packet. You can perform the classification based on Layer 2 MAC, IP-standard, or IP-extended
access control lists (ACLs). Standard QoS also offers single-rate or aggregate traffic policing on ingress.
Drop policy actions are passing through the packet without modification, marking down the assigned
DSCP in the packet, or dropping the packet. Standard QoS performs ingress queueing based on the
weighted tail drop (WTD) algorithm and ingress scheduling based on shaped round robin (SRR). On
egress, standard QoS offers queueing based on WTD and scheduling based on SRR shared or shaped
weights.
You can use hierarchical QoS to classify, police, mark, queue, and schedule outbound traffic on an
enhanced-services (ES) port. On egress, hierarchical QoS offers classification based on the CoS, DSCP,
IP precedence, or the multiprotocol label switching (MPLS) experimental (EXP) bits in the outbound
packet. You also can classify a packet based on its VLAN. Hierarchical QoS offers two-rate traffic
policing on egress. Drop policy actions are passing through the packet without modification; marking
down the CoS, DSCP, IP precedence, or the MPLS EXP bits in the packet; or dropping the packet.
Hierarchical QoS performs egress queueing based on tail drop or Weighted Random Early Detection
(WRED). The queue scheduling management features is class-based weighted fair queueing (CBWFQ),
and the scheduling congestion-management features is low-latency queueing (LLQ). You can use traffic
shaping to decrease the burstiness of traffic.
For information about multiprotocol label switching (MPLS), Ethernet over MPLS (EoMPLS), and QoS,
see the "Configuring MPLS and EoMPLS QoS" section on page 30-18.
Note For complete syntax and usage information for the commands used in this chapter, refer to the command
reference this release.
Catalyst 3750 Metro Switch Software Configuration Guide
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