Optimizing Converged Cisco Networks (ONT)
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Transcript of Optimizing Converged Cisco Networks (ONT)
© 2006 Cisco Systems, Inc. All rights reserved.
Optimizing Converged Cisco Networks (ONT)
Module 4: Implement the DiffServ QoS Model
© 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.
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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
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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.
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Classification and Marking in the Enterprise
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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.
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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
7 6 5 4 3 2 1 0
ID Offset TTL Proto FCS IP SA IP DA DataLenVersion Length
ToSByte
DiffServ Code Point (DSCP) IP ECN
IPv4 Packet
IP Precedence UnusedStandard IPv4
DiffServ Extensions
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IP ToS Byte and DS Field Inside the IP Header
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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.
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Per-Hop Behaviors
DSCP selects PHB throughout the network:Default PHB (FIFO, tail drop)
Class-selector PHB (IP precedence)
EF PHB
AF PHB
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Standard PHB Groups
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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
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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
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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.
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Mapping CoS to Network Layer QoS
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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)
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Implementing QoS Policy Using a QoS Service Class
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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.
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Classification and Marking DesignQoS Baseline Marking Recommendations
ApplicationL3 Classification
DSCPPHBIPP CoS
Transactional Data 18AF212 2
Call Signaling 24CS3*3 3
Streaming Video 32CS44 4
Video Conferencing 34AF414 4
Voice 46EF5 5
Network Management 16CS22 2
L2
Bulk Data 10AF111 1
Scavenger 8CS11 1
Routing 48CS66 6
Mission-Critical Data 26AF31*3 3
Best Effort 000 0
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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
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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
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Trust Boundaries: Mark Where?
For scalability, marking should be done as close to the source as possible.
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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?
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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.
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Q and A
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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 Modelhttp://www.cisco.com/en/US/partner/products/ps6610/products_data_sheet0900aecd8031b36d.html
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