Which element is mandatory for QoS policy propagation through BGP operations? (Exhibit)
A.
MPLS
B.
NBAR
C.
CEF
D.
QoS pre-classify
E.
policy-based routing
F.
MQC
Explanation:
Common Classification
Classification is the process of defining traffic classes that sort traffic into categories groups of flows. Classification defines the “match criteria” for each class of traffic that is to be treated by a QoS policy. More specifically, it defines the “traffic filter” that packets are checked against when a service-policy is applied.
Both distributed and non-distributed platforms match packets to a single class in a policy-map. Matching terminates at the first matching class. If two classes within a policy-map match the same IP precedence or IP address range, the packet always belongs to the first matching class. For this reason, class order within a policy-map is very important. This classification approach is called “common classification” and has these benefits:
* Accurate accounting and the avoidance of double-accounting problems that were seen before “common classification”.
* Reduces the impact of access control lists (ACLs) on the CPU since the ACL is checked once per class, rather than once per feature.
* Faster lookup of packet headers because of caching.
Common classification is enabled automatically when you attach an input or output policy-map with the service-policy command.
The table below illustrates the order of operation with common classification. It is important to understand from the table when classification occurs in the context of QoS features. On the inbound path, a packet is classified before it is switched. On the outbound path, a packet is classified after it is switched.Note: Inbound Network-Based Application Recognition (NBAR) happens after ACLs and before policy-based routing.
Important changes have been implemented regarding feature ordering and remarked value usage. These changes include moving input CAR, input MAC, and IP precedence accounting functions to occur before MQC output classification: Input rate-limiting, or CAR, applies to packets following the process switching path and destined to the router. Previously, only packets switched through the router using CEF could be rate-limited. New IP precedence values set by input CAR or QPPB can be used for selecting a Virtual Circuit (VC) in an ATM VC bundle. IP precedence, Differentiated Services Code Points (DSCP), and QoS group values set by input CAR or QPPB can be used for MQC output packet classification.