| Exam 642-887 | Question id=3196 | QOS in a Service Provider IP NGN Environment |
When configuring class-based WRED on Cisco routers, which WRED parameter is not user configurable on a Cisco IOS XR but is user configurable on a Cisco IOS and IOS XE?
| A. |
the ingress or egress direction where the class-based WRED policy will be applied | |
| B. |
the maximum threshold | |
| C. |
the minimum threshold | |
| D. |
the mark probability denominator |
The Cisco IOS-XR software implementation of QoS is basically the same as the QoS implementation on Cisco IOS software, with the following exceptions:
·On Cisco IOS-XR software, the bandwidth command can be configured only in egress policies. ·The following changes have been made to the class-map command on Cisco IOS-XR software:
-Supports 4K per logical router.
-Maximum number of match criteria configurable in one class map is eight.
·When a class is marked as high priority using the priority command on Cisco IOS-XR software, we recommend that you configure a policer to limit the priority traffic. Limiting the priority traffic will ensure that the priority traffic does not starve all of the other traffic on the line card. Use the police command to explicitly configure the policer.
·On Cisco IO-XR software, only one conform-action, exceed-action, or violate-action command can be configured at a time. To configure traffic policing, use the police command. ·On Cisco IOS-XR software, policy modifications cannot be made on existing policies. Use the policy-map command to remove the policy from all attached interfaces, delete the policy map, and redefine a new policy.
·When configuring a policy map on Cisco IOS-XR software, the maximum number of classes configurable in one policy map is 16, which includes both Level 1 and Level 2 classes. To configure a policy map, use the policy-map command.
·When WRED is configured on Cisco IOS-XR software, the mark probability in the random-detect command is not configurable--it is always set to 1.
·When the random-detect exp command is used on Cisco IOS-XR software, the exponential weighting constant is not configurable and will be programmed automatically by Cisco IOS-XR software.
·When access control lists (ACLs) are used in QoS class maps, the underlying deny or permit actions associated with access control entries (ACEs) are ignored. ACEs are used as a classification mechanism in order to provide appropriate QoS behavior as specified in class maps.
Use ACLs that include ACEs with permit actions only.