Cisco 3845 Software Guide - Page 513

Chapter 27 Configuring QoS Configuring QoS • Egress classification for a class of traffic that has been acted on by an input policy-map can take place only on the per-hop behavior criteria and value established by the input policy-map. - If a class in an input policy-map is classifying based on per-hop behavior criteria and is configured for policing but not marking, then the per-hop behavior established by the input policy-map for that class of traffic is the classification criteria and value in the associated class-map. - If a class in an input policy-map is not classifying on per-hop behavior criteria, but is classifying on flow criteria by using a MAC ACL or IP ACL, and it is configured for policing, a default best-effort per-hop behavior is established for that class of traffic. Traffic in this class is not eligible for egress classification based on per-hop behavior criteria. - If a class in an input policy-map is configured for marking, the per-hop behavior established by the input policy-map for that class of traffic is the marked per-hop behavior criteria and value. - If a class in an input policy-map is not configured for any action (class-default), a default best-effort per-hop behavior is established for that class of traffic. Traffic in this class is not eligible for egress classification based on PHB-criteria. For example: if the per-hop behavior established for a class of traffic by an input policy-map is DSCP ef, you can classify that class of traffic on the egress based only on DSCP ef and not on any other mutually exclusive per-hop behavior such as outer CoS or inner CoS. • Egress classification on a target with no input policy map attached can use any classification criteria specified in the egress policy. When an input policy map is attached to a target, even if traffic does not match any classes in the input policy, it cannot be egress-classified. • When configuring both MPLS VPN and QoS, you can apply most QoS functions to MPLS VPN traffic. However, for a hierarchical QoS function, you cannot apply a service policy that would match traffic on a per-VRF basis because VRFs are dynamically assigned to an MPLS label. For MPLS VPN traffic, you can apply a service-policy on egress traffic that matches traffic based on DSCP or MPLS. For information about configuring QoS with MPLS and EoMPLS, see the "Configuring MPLS and EoMPLS QoS" section on page 27-53. • There is a limitation per bridge-domain on the number of unique flows classified on inner or outer VLANs that you can configure for egress classification. An error message appears when this limitation is exceeded. • Hierarchical marking and policing are not supported. You can configure marking and policing for any number of classes on any one of the three levels of the policy-map hierarchy. If you configure marking on one level, you can configure policing without marking (transmit, drop) on another level. • An EFP can support only 2-level egress scheduling policies. If you attach a 3-level hierarchical policy to an EFP, only 2 of the 3 levels can have scheduling actions (bandwidth, shape, or priority) • There is a limitation on the maximum number of unique per-hop behavior-criteria combinations that can be configured on the system. The limit is internally calculated and is a function of input classification, marking, and egress classification based on per-hop behavior. An error message appears when this limit is reached. Configuring Input Policy Maps • Configuring Input Class Maps, page 27-26 • Using ACLs to Classify Traffic, page 27-28 • Configuring Class-Based Marking, page 27-32 • Configuring Policing, page 27-34 OL-23400-01 Cisco ME 3800X and 3600X Switch Software Configuration Guide 27-25