© 2006 Cisco Systems, Inc. All rights reserved. Module 4: Implement the DiffServ QoS Model Lesson 4.1: Introducing Classification and Marking

© 2006 Cisco Systems, Inc. All rights reserved. Objectives  Describe the classification and marking for QoS.  Explain the relationship between IP Precedence and DSCP.  Describe the standard Per Hop Behavior (PHB) groups and their characteristics.  Explain how a service class is used to implement QoS policies.  Describe a trust boundary and the guidelines used to establish this boundary.

© 2006 Cisco Systems, Inc. All rights reserved. Classification  Classification is the process of identifying and categorizing traffic into classes, typically based upon: Incoming interface IP precedence DSCP Source or destination address Application  Without classification, all packets are treated the same.  Classification should take place as close to the source as possible.

© 2006 Cisco Systems, Inc. All rights reserved. Marking  Marking is the QoS feature component that “colors” a packet (frame) so it can be identified and distinguished from other packets (frames) in QoS treatment.  Commonly used markers: Link layer: CoS (ISL, 802.1p) MPLS EXP bits Frame Relay Network layer: DSCP IP precedence

© 2006 Cisco Systems, Inc. All rights reserved. Useful Links  configuration/voip-qos-settings-part-2/ configuration/voip-qos-settings-part-2/   nexus1000/sw/4_0/qos/configuration/guide/qos_6dscp_ val.pdf nexus1000/sw/4_0/qos/configuration/guide/qos_6dscp_ val.pdf

© 2006 Cisco Systems, Inc. All rights reserved. Classification and Marking in the LAN with IEEE 802.1Q  IEEE 802.1p user priority field is also called CoS.  IEEE 802.1p supports up to eight CoSs.  IEEE 802.1p focuses on support for QoS over LANs and 802.1Q ports.  IEEE 802.1p is preserved through the LAN, not end to end.

© 2006 Cisco Systems, Inc. All rights reserved. Classification and Marking in the Enterprise

© 2006 Cisco Systems, Inc. All rights reserved. DiffServ Model  Describes services associated with traffic classes, rather than traffic flows.  Complex traffic classification and conditioning is performed at the network edge.  No per-flow state in the core.  The goal of the DiffServ model is scalability.  Interoperability with non-DiffServ-compliant nodes.  Incremental deployment.

© 2006 Cisco Systems, Inc. All rights reserved. Classification Tools IP Precedence and DiffServ Code Points  IPv4: three most significant bits of ToS byte are called IP Precedence (IPP)—other bits unused  DiffServ: six most significant bits of ToS byte are called DiffServ Code Point (DSCP)—remaining two bits used for flow control  DSCP is backward-compatible with IP precedence IDOffsetTTLProtoFCSIP SAIP DADataLen Version Length ToS Byte DiffServ Code Point (DSCP)IP ECN IPv4 Packet IP PrecedenceUnused Standard IPv4 DiffServ Extensions

© 2006 Cisco Systems, Inc. All rights reserved. IP ToS Byte and DS Field Inside the IP Header

© 2006 Cisco Systems, Inc. All rights reserved. IP Precedence and DSCP Compatibility  Compatibility with current IP precedence usage (RFC 1812)  Differentiates probability of timely forwarding: (xyz000) >= (abc000) if xyz > abc  That is, if a packet has DSCP value of , it has a greater probability of timely forwarding than a packet with DSCP value of

© 2006 Cisco Systems, Inc. All rights reserved. Per-Hop Behaviors  DSCP selects PHB throughout the network: Default PHB (FIFO, tail drop) Class-selector PHB (IP precedence) EF PHB AF PHB

© 2006 Cisco Systems, Inc. All rights reserved. Standard PHB Groups

© 2006 Cisco Systems, Inc. All rights reserved. Expedited Forwarding (EF) PHB  EF PHB: Ensures a minimum departure rate Guarantees bandwidth—class guaranteed an amount of bandwidth with prioritized forwarding Polices bandwidth—class not allowed to exceed the guaranteed amount (excess traffic is dropped)  DSCP value of : Looks like IP precedence 5 to non-DiffServ- compliant devices: Bits 5 to 7: 101 = 5 (same 3 bits are used for IP precedence) Bits 3 and 4: 11 = No drop probability Bit 2: Just 0

© 2006 Cisco Systems, Inc. All rights reserved. Assured Forwarding (AF) PHB  AF PHB: Guarantees bandwidth Allows access to extra bandwidth, if available  Four standard classes: AF1, AF2, AF3, and AF4  DSCP value range of aaadd0: aaa is a binary value of the class dd is drop probability

© 2006 Cisco Systems, Inc. All rights reserved. AF PHB Values  Each AF class uses three DSCP values.  Each AF class is independently forwarded with its guaranteed bandwidth.  Congestion avoidance is used within each class to prevent congestion within the class.

© 2006 Cisco Systems, Inc. All rights reserved. Mapping CoS to Network Layer QoS

© 2006 Cisco Systems, Inc. All rights reserved. QoS Service Class  A QoS service class is a logical grouping of packets that are to receive a similar level of applied quality.  A QoS service class can be: A single user (such as MAC address or IP address) A department, customer (such as subnet or interface) An application (such as port numbers or URL) A network destination (such as tunnel interface or VPN)

© 2006 Cisco Systems, Inc. All rights reserved. Implementing QoS Policy Using a QoS Service Class

© 2006 Cisco Systems, Inc. All rights reserved. QoS Service Class Guidelines  Profile applications to their basic network requirements.  Do not over engineer provisioning; use no more than four to five traffic classes for data traffic: Voice applications: VoIP Mission-critical applications: Oracle, SAP, SNA Interactive applications: Telnet, TN3270 Bulk applications: FTP, TFTP Best-effort applications: , web Scavenger applications: Nonorganizational streaming and video applications (Kazaa, Yahoo)  Do not assign more than three applications to mission-critical or transactional classes.  Use proactive policies before reactive (policing) policies.  Seek executive endorsement of relative ranking of application priority prior to rolling out QoS policies for data.

© 2006 Cisco Systems, Inc. All rights reserved. Classification and Marking Design QoS Baseline Marking Recommendations Application L3 Classification DSCPPHBIPPCoS Transactional Data 18AF2122 Call Signaling24CS3*33 Streaming Video 32CS444 Video Conferencing34AF4144 Voice46EF55 Network Management16CS222 L2 Bulk Data10AF1111 Scavenger8CS111 Routing48CS666 Mission-Critical Data26AF31*33 Best Effort0000

© 2006 Cisco Systems, Inc. All rights reserved. How Many Classes of Service Do I Need? 4/5 Class Model Scavenger Critical Data Call Signaling Realtime 8 Class Model Critical Data Video Call Signaling Best Effort Voice Bulk Data Network Control Scavenger 11 Class Model Network Management Call Signaling Streaming Video Transactional Data Interactive-Video Voice Best Effort IP Routing Mission-Critical Data Scavenger Bulk Data Time Best Effort

© 2006 Cisco Systems, Inc. All rights reserved. Trust Boundaries: Classify Where?  For scalability, classification should be enabled as close to the edge as possible, depending on the capabilities of the device at: Endpoint or end system Access layer Distribution layer

© 2006 Cisco Systems, Inc. All rights reserved. Trust Boundaries: Mark Where?  For scalability, marking should be done as close to the source as possible.

© 2006 Cisco Systems, Inc. All rights reserved. Self Check 1.Which PHB would be used for voice traffic? 2.How many bits are used for IP Precedence? For DSCP? 3.Which PHB can allow access to extra bandwidth if it is available? 4.How is CDP used to establish trust boundaries?

© 2006 Cisco Systems, Inc. All rights reserved. Summary  Classification, marking, and queuing are critical functions of any successful QoS implementation.  Classification allows network devices to identify traffic as belonging to a specific class with the specific QoS requirements determined by an administrative QoS policy.  The DiffServ model uses classes to describe services offered to network traffic, rather than traffic flows.  DiffServ uses DSCP to establish Per Hop Behaviors (PHBs) to classify and service traffic.