Transcript CCNP4v5.0

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
 http://kb.smartvox.co.uk/ip-phones/sipconfiguration/voip-qos-settings-part-2/
 http://www.rhyshaden.com/qos.htm
 http://www.cisco.com/en/US/docs/switches/datacenter/
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
ToS
Byte
Version
Length
Len
ID
Offset
TTL
Proto
FCS
IP SA
IP DA
Data
IPv4 Packet
7
6
5
4
IP Precedence
3
2
1
0
Standard IPv4
Unused
DiffServ Code Point (DSCP)
IP ECN
DiffServ Extensions
 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
© 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 011000, it has a greater
probability of timely forwarding than a packet with DSCP value of
001000.
© 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 101110: Looks like IP precedence 5 to non-DiffServcompliant 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
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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)
© 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: 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.
© 2006 Cisco Systems, Inc. All rights reserved.
Classification and Marking Design
QoS Baseline Marking Recommendations
Application
L3 Classification
L2
IPP
PHB
DSCP
CoS
Routing
6
CS6
48
6
Voice
5
EF
46
5
Video Conferencing
4
AF41
34
4
Streaming Video
4
CS4
32
4
Mission-Critical Data
3
AF31*
26
3
Call Signaling
3
CS3*
24
3
Transactional Data
2
AF21
18
2
Network Management
2
CS2
16
2
Bulk Data
1
AF11
10
1
Best Effort
0
0
0
0
Scavenger
1
CS1
8
1
© 2006 Cisco Systems, Inc. All rights reserved.
How Many Classes of Service Do I Need?
4/5 Class Model
8 Class Model
11 Class Model
Voice
Voice
Realtime
Call Signaling
Interactive-Video
Video
Streaming Video
Call Signaling
Call Signaling
IP Routing
Network Control
Critical Data
Critical Data
Network Management
Mission-Critical Data
Transactional Data
Bulk Data
Bulk Data
Best Effort
Best Effort
Best Effort
Scavenger
Time
Scavenger
Scavenger
© 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.
© 2006 Cisco Systems, Inc. All rights reserved.