Make sure the new configurations still conform to the design and implementation from the previous example

The same service policy will be configured in this example. In this case, however, DSCP-based classes of service are used. Remember that the DiffServ model itself provides defined traffic classes and their associated PHB. DiffServ-based classification is used in this example as follows:

■ Mission-critical class: Marked using DSCP AF class 2, and should get 30 percent of an interface bandwidth

■ Bulk class: Marked using DSCP AF class 1, and should get 20 percent of the interface bandwidth

■ Best-effort class: Traffic should get the remaining bandwidth share, and should be fair-queued

To enforce this service policy, a router will use CBWFQ to perform bandwidth sharing, and will use WRED within service classes to perform differentiated drop.

Example: CB-WRED Using DSCP with CBWFQ (Cont.)

The configuration example shows how traffic classification is performed using DSCP-based classes, representing the mission-critical class as the AF1 class, and the AF2 class as the bulk class. WRED DSCP-based parameters are set reflecting the class-dependent drop strategy, as follows:

■ The mission-critical class is guaranteed at least 30 percent of bandwidth, with a custom WRED profile which establishes three different drop probabilities for AF class 2.

■ The bulk class is guaranteed at least 20 percent of bandwidth, is configured with three different drop probabilities for AF class 1, and has a somewhat lower WRED maximum threshold. As a result, bulk-class traffic is more likely to be dropped than the mission-critical class in the event of interface congestion.

All other traffic is part of the default class, and is fair-queued, with default WRED parameters.

This topic describes the Cisco IOS commands that are required to monitor CB-WRED.

Monitoring CB-WRED

router#

show policy-map interface interface-name

• Displays the configuration of all classes configured for all service policies on the specified interface

• Displays the configuration of all classes configured for all service policies on the specified interface

Use the show policy-map interface command to display the configuration of all classes configured for all service policies on the specified interface. This includes all WRED parameters implementing the drop policy on the specified interface.

The table explains some of the key fields of the output of the show policy-map interface command.

show policy-map interface Output Fields

Field

Description

service-policy output

Name of the output service policy applied to the specified interface or VC.

class-map

Class of traffic being displayed. Output is displayed for each configured class in the policy. The choice for implementing class matches (for example, match-all or match-any) can also appear next to the traffic class.

match

Match criteria specified for the class of traffic. Choices include criteria such as IP precedence, IP DSCP value, Multiprotocol Label Switching (MPLS) experimental value, access groups, and QoS groups.

exponential weight

Exponent used in the average queue size calculation for a WRED parameter group.

mean queue depth

Average queue depth based on the actual queue depth on the interface and the exponential weighting constant. It is a fluctuating average. The minimum and maximum thresholds are compared against this value to determine drop decisions.

Was this article helpful?

0 0

Post a comment