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User Guide for Cisco Security Manager 4.4
OL-28826-01
Chapter 63 Configuring Quality of Service
Quality of Service on Cisco IOS Routers
After you create your interface definitions, you must define one or more QoS classes on each interface.
QoS classes contain the matching criteria that determine which packets are included in the class and the
QoS functions (marking, queuing, policing, and shaping) to apply to that traffic. You can configure each
interface (or interface role) with up to 16 QoS classes, each containing its own set of matching criteria
and a defined set of QoS functions to apply to the traffic in that class.
For each interface, we recommend that for each interface you define at least one QoS class and a default
class. If you do not configure a default class, packets that do not match the criteria of the other defined
classes are treated as members of a default class that has no configured QoS functionality. Packets
assigned to this class are placed in a simple first-in first-out (FIFO) queue, and are forwarded at a rate
determined by the available underlying link bandwidth. This FIFO queue is managed by tail drop, which
avoids congestion by dropping packets from the queue until it is no longer full.
Note QoS is applied to packets on a first-match basis. The router examines the table of QoS classes starting
from the top and applies the properties of the first class whose matching criteria matches the packet.
Therefore, it is important that you define and order your classes carefully. The default class should be
placed last to prevent traffic that matches a specific class from being treated as unmatched traffic.
Before You Begin
Ensure that Cisco Express Forwarding (CEF) is enabled on the router. For more information, see CEF
Interface Settings on Cisco IOS Routers, page 59-24.
Related Topics
• Defining QoS Policies, page 63-10
• Defining QoS on the Control Plane, page 63-12
• Quality of Service on Cisco IOS Routers, page 63-1
Step 1 Do one of the following:
• (Device view) Select Platform > Quality of Service from the Policy selector.
• (Policy view) Select Router Platform > Quality of Service from the Policy Type selector. Select
an existing policy or create a new one.
The Quality of Service page is displayed. See Table 63-3 on page 63-20 for a description of the fields
on this page.
Step 2 In the Applied to field, select Interfaces to define QoS parameters for specific interfaces on the selected
router.
Step 3 Click the Add button under the upper table to display the QoS Policy dialog box. See Table 63-4 on
page 63-21 for a description of the fields in this dialog box.
Step 4 In the Interface field, enter the name of an interface or interface role, or click Select to display a selector.
Tip If the interface role you want is not listed in the selector, click the Create button or the Edit
button to open the Interface Role Dialog Box, page 6-69. From here you can define an interface
role to use in the policy.
Step 5 Select the traffic direction on which you want to apply the QoS definition, Output (traffic exiting the
interface) or Input (traffic entering the interface). Queuing and shaping can be applied only to output
traffic.