Mechanics of MQC

·         MQC separates the classification function of a QoS tool from the action (PHB) that the QoS tool wants to perform.

·         There are 3 major commands with MQC, with several subordinate commands:

o   Class-map: define the matching parameters for classifying packets into service classes

o   Policy-map: Under this command the PHB actions(marking, queuing, and so on) are configured

o   Service-map: under this command a policy map is enabled on an interface.

·         QoS policy treat packets in one off 2 categories, called QoS service classes.

·         Classify the packets into 2 classes for the use of calling the two class-map commands

·         Each class-map command would be followed by match subcommand

§  Match subcommand defines the actual parameters that are compared to the frame/packet header contents to match packets for classification.

·         For each class, some QoS action (PHB) is to be performed.

o   This action is configured using the policy-map command

o   Under a single policy map, multiple classes can be referenced

·         When the service-policy command is applied to an interface,

o   the QoS features are enabled either inbound or outbound on that interface

Cisco Modular QoS CLI

·         In every ios relese, cisco adds some QoS features & functions,

o   Each of which has its own separate set of configurations and exec commands

·         There are many different QoS tools & different QoS commands,

o   QoS configuration became a big chore(specific configuration for specific work)

·         Cisco creates the MQC to help resolve these problems,

o   By defining a common set of configuration commands to configure many QoS features in a router or switch.

·         MQC is not totally new CLI

o   It is a method of categorizing

·         IOS classification

·         Marking and related actions

o   Into a logical groupings to unify the Command-Line Interface

·         MQC defines a new set of configuration commands

o   Commands that are typed in using the same ios CLI, in configuration mode.

·         In MQC, one new command to know how to configure any additional MQC based QoS tools

·         We can identify MQC based tools by the name of the tool

§  They all begin with the phrase “class-based” (CB)

§  These tools include

·         CB Marking

·         CB Weighted Fair Queing (CBWFQ)

·         CB Policing

·         CB Shaping

·         CB Header Compression

LOCATOIONS FOR MARKING AND MATCHING

·         Some devices may not able to look at the IPP or DSCP fields

o   For instance, an MPLS LSR make QoS decision on based on the 3-bit MPLS EXP field in the MPLS label

§  But unable to look at the encapsulated IP header and DSCP field

o   In such cases, QoS tools configured on edge devices to look at the DSCP & then mark a different field.

·         The non-IP header markable fields exist in only parts of the network.

o   Those fields can be used for classification or marking only on the appropriate interfaces

·         The rules for where these fields (CoS, DE, CLP, EXP) can be used are as follows:

o   For Classification:

§  On ingress only, and only if the interface supports that particular header field

o   For Marking:

§  On egress only, and only if the interface supports that particular header field

Summarizes the QoS marking fields

Field	Location	Length
IP Precedence	IP header	3bits
IP DSCP	IP header	6 bits
DS field	IP header	1byte
ToS byte	IP header	1byte
CoS	ISL & 802.1Q header	3bits
Discard Eligible(DE)	FrameRelay header	1bit
Cell Loss Priority(CLP)	ATM cell header	1bit
MPLS Experimental	MPLS header	3bits