Cisco Systems 4500 Configuring QoS on Supervisor Engines II-Plus, II+10GE, IV, V, V-10GE, 4924, 4948, and 4948-10GE

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Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 37 Configuring Quality of Service Configuring QoS on Supervisor Engines II-Plus, II+10GE, IV, V, V-10GE, 4924, 4948, and 4948-10GE
However, Cisco IOS marks all the generated control packets appropriately and uses the internal IP DSCP
to determine the transmit queue on the output transmission interface. For IP packets, the internal IP
DSCP is the IP DSCP field in the IP packet. For non-IP packets, Cisco IOS assigns a packet priority
internally and maps it to an internal IP DSCP value.
Cisco IOS assigns an IP precedence of 6 to routing protocol packets on the control plane. As noted in
RFC 791, “The Internetwork Control designation is intended for use by gateway control originators
only.” Specifically, Cisco IOS marks the following IP-based control packets: Open Shortest Path First
(OSPF), Routing Information Protocol (RIP), Enhanced Interior Gateway Routing Protocol (EIGRP)
hellos, and keepalives. Telnet packets to and from the router also receive an IP precedence value of 6.
The assigned value remains with the packets when the output interface transmits them into the network.
For Layer 2 control protocols, the software assigns an internal IP DSCP. Typically, Layer 2 control
protocol packets are assigned an internal DSCP value of 48 (corresponding to an IP precedence value of
6).
The internal IP DSCP is used to determine the transmit queue to which the packet is enqueued on the
transmission interface. See “Configuring Transmit Queues” on page 50 for details on how to configure
the DSCP to transmit queues.
The internal IP DSCP is also used to determine the transmit CoS marking if the packet is transmitted
with a IEEE 802.1q or ISL tag on a trunk interface. See “Configuring the DSCP-to-CoS Map” on page 55
for details on how to configure the DSCP to CoS mapping.
Configuring QoS on Supervisor Engines II-Plus, II+10GE, IV, V,
V-10GE, 4924, 4948, and 4948-10GE
Before configuring QoS, you must have a thorough understanding of these items:
• The types of applications used and the traffic patterns on your network.
• Traffic characteristics and needs of your network. Is the traffic bursty? Do you need to reserve
bandwidth for voice and video streams?
• Bandwidth requirements and speed of the network.
• Location of congestion points in the network.
These sections describe how to configure QoS on the Catalyst 4500 family switch:
• Default QoS Configuration, page 37-18
• Configuration Guidelines, page 37-19
• Enabling QoS Globally, page 37-20
• Configuring a Trusted Boundary to Ensure Port Security, page 37-21
• Enabling Dynamic Buffer Limiting, page 37-22
• Creating Named Aggregate Policers, page 37-26
• Configuring a QoS Policy, page 37-28
• Configuring CoS Mutation, page 37-36
• Configuring User-Based Rate-Limiting, page 37-37
• Enabling Per-Port Per-VLAN QoS, page 37-43
• Enabling or Disabling QoS on an Interface, page 37-46
• Configuring VLAN-Based QoS on Layer 2 Interfaces, page 37-46