Optimizing Converged Cisco Networks (ONT)

1. Optimizing Converged Cisco Networks (ONT) Module 4: Implement the DiffServ QoS Model

2. Module 4: Implement the DiffServ QoS Model Lesson 4.1: Introducing Classification and Marking

3. 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.

4. 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.

5. 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

6. 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.

7. Classification and Marking in the Enterprise

8. 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.

9. 7 6 5 4 3 2 1 0 Standard IPv4 IP Precedence Unused DiffServ Code Point (DSCP) IP ECN DiffServ Extensions Classification ToolsIP 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 ToS Byte Version Length Len ID Offset TTL Proto FCS IP SA IP DA Data IPv4 Packet

10. IP ToS Byte and DS Field Inside the IP Header

11. 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 011000, it has a greater probability of timely forwarding than a packet with DSCP value of 001000.

12. Per-Hop Behaviors • DSCP selects PHB throughout the network: • Default PHB (FIFO, tail drop) • Class-selector PHB (IP precedence) • EF PHB • AF PHB

13. Standard PHB Groups

14. 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 101110: 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

15. 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

16. 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.

17. Mapping CoS to Network Layer QoS

18. 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)

19. Implementing QoS Policy Using a QoS Service Class

20. 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: E-mail, 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.

21. Application L3 Classification L2 IPP PHB DSCP CoS Routing 6 CS6 48 6 Voice 5 EF 46 5 Video Conferencing 4 AF41 34 4 4 CS4 32 4 Streaming Video Mission-Critical Data 3 AF31* 26 3 Call Signaling 3 CS3* 24 3 2 AF21 18 2 Transactional Data Network Management 2 CS2 16 2 Bulk Data 1 AF11 10 1 Scavenger 1 CS1 8 1 Best Effort 0 0 0 0 Classification and Marking DesignQoS Baseline Marking Recommendations

22. 8 Class Model 11 Class Model Voice Voice Interactive-Video Video Streaming Video Call Signaling Call Signaling IP Routing Network Control Network Management Critical Data Mission-Critical Data Transactional Data Bulk Data Bulk Data Best Effort Best Effort Time Scavenger Scavenger How Many Classes of Service Do I Need? 4/5 Class Model Realtime Call Signaling Critical Data Best Effort Scavenger

23. 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

24. Trust Boundaries: Mark Where? • For scalability, marking should be done as close to the source as possible.

25. Self Check • Which PHB would be used for voice traffic? • How many bits are used for IP Precedence? For DSCP? • Which PHB can allow access to extra bandwidth if it is available? • How is CDP used to establish trust boundaries?

26. 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.

27. Q and A

28. Resources • DiffServ -- The Scalable End-to-End QoS Model • http://www.cisco.com/en/US/partner/products/ps6610/products_white_paper09186a00800a3e2f.shtml • Quality of Service - The Differentiated Services Model • http://www.cisco.com/en/US/partner/products/ps6610/products_data_sheet0900aecd8031b36d.html