Optimizing Converged Cisco Networks (ONT) · Mission-critical applications: Oracle, SAP, SNA...

© 2006 Cisco Systems, Inc. All rights reserved.

Optimizing Converged Cisco Networks (ONT)

Module 4: Implement the DiffServ QoS Model (Intro)


Introducing Classification and Marking


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.


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.


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


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.


Classification and Marking in the Enterprise


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.


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


IP ToS Byte and DS Field Inside the IP Header

7 6 5 4 3 2 1 0

7 6 5 4 3 2 1 0


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.


Per-Hop Behaviors

DSCP selects PHB throughout the network:

Default PHB (FIFO, tail drop)

Class-selector PHB (IP precedence)

EF Expedite Forwarding PHB

AF Assured Forwarding PHB


Standard PHB Groups


Expedited Forwarding (EF) PHB

EF PHB:

• Ensures a minimum departure rate (lowest delay)

• 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 (contradiction to AF PHB)

Bit 2: Just 0


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


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.

Probability of drop, a relationship where AFx1 <= AFx2 <= AFx3.


Mapping CoS to Network Layer QoS

En

d-t

o-e

nd

Qo

S


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)


Implementing QoS Policy Using a QoS Service Class


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, Youtube)

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.


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

* Cisco IP phones use AF31 currently for call-signaling => MCD = DSCP 25


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


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

If a endpoint is trusted then enable mls qos trust dscp in the sw.


Trust Boundaries: Mark Where?

For scalability, marking should be done as close to the source as possible.


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?


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.


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

Differentiated_services

http://en.wikipedia.org/wiki/Differentiated_services





http://en.wikipedia.org/wiki/Differentiated_services



Using NBAR for Classification


Network-Based Application Recognition

Used in conjunction with QoS class-based features, NBAR is an intelligent classification engine that:

Classifies modern client-server and web-based applications

Discovers what traffic is running on the network

Analyzes application traffic patterns in real time

NBAR functions:Performs identification of applications and protocols (Layer 4–7)

Performs protocol discovery

Provides traffic statistics

New applications are easily supported by loading a Packet Description Language Module (PDLM).

My application

is too slow!

Sample Link Utilization

Citrix 25%Netshow 15%Fasttrack 10%FTP 30%HTTP 20%


NBAR Functions & Features

NBAR performs the following two functions:

Identification of applications and protocols (Layer 4 to Layer 7)

Protocol discovery (statistics)

Some examples of class-based QoS features that can be used on traffic after the traffic is classified by NBAR include:

Class-Based Marking (the set command)

Class-Based Weighted Fair Queueing (the bandwidth and queue-limit commands)

Low Latency Queueing (the priority command)

Traffic Policing (the police command)

Traffic Shaping (the shape command)


NBAR Application Support

NBAR can classify applications that use:

Statically assigned TCP and UDP port numbers

Non-UDP and non-TCP IP protocols

Dynamically assigned TCP and UDP port numbers negotiated during connection establishment (requires stateful inspection)

Subport and deep packet inspection classification

Restrictions: You must enable Cisco Express Forwarding (CEF) before you configure NBAR.


Packet Description Language Module

PDLMs allow NBAR to recognize new protocols matching text patterns in data packets without requiring a new Cisco IOS software image or a router reload.

An external PDLM can be loaded at run time to extend the NBAR list of recognized protocols.

PDLMs can also be used to enhance an existing protocol recognition capability.

PDLMs must be produced by Cisco engineers.

CCO registered users can find the PDLMs at: http://www.cisco.com/cgi-bin/tablebuild.pl/pdlm.

http://www.cisco.com/cgi-bin/tablebuild.pl/pdlm




NBAR Command Syntax

Used to enhance the list of protocols recognized by NBAR through a PDLM.

The filename is in the URL format (for example, flash://citrix.pdlm).

ip nbar pdlm pdlm-name

router(config)#

ip nbar port-map protocol-name [tcp | udp] port-

number

router(config)#

Configures NBAR to search for a protocol or protocol name using a port number other than the well-known port.

Up to 16 additional port numbers can be specified.

Example: ip nbar port-map http tcp 80 8080


NBAR Show Protocol-to-Port Maps

Displays the current NBAR protocol-to-port mappings

router#show ip nbar port-map

port-map bgp udp 179

port-map bgp tcp 179

port-map cuseeme udp 7648 7649

port-map cuseeme tcp 7648 7649

port-map dhcp udp 67 68

port-map dhcp tcp 67 68

port-map dns udp 53

port-map dns tcp 53

Port-map http tcp 80 8080

show ip nbar port-map [protocol-name]

router#


NBAR Protocol Discovery

Analyzes application traffic patterns in real time and discovers which traffic is running on the network

Provides bidirectional, per-interface, and per-protocol statistics

Important monitoring tool supported by Cisco QoS management tools:

Generates real-time application statistics

Provides traffic distribution information at key network locations


Configuring and Monitoring NBAR Protocol Discovery

Configures NBAR to discover traffic for all protocols known to NBAR on a particular interface

Requires that CEF be enabled before protocol discovery

Can be applied with or without a service policy enabled

ip nbar protocol-discovery

router(config-if)#

show ip nbar protocol-discovery

router#

Displays the statistics for all interfaces on which protocol discovery is enabled. Statistics can be inaccurate because of policing of queue drops at the output interface.


Configuring and Monitoring Protocol Discovery Output

router#show ip nbar protocol-discovery

Ethernet0/0

Input Output

Protocol Packet Count Packet Count

Byte Count Byte Count

5 minute bit rate (bps) 5 minute bit rate (bps)

---------- ------------------------ -----------------

realaudio 2911 3040

1678304 198406

19000 1000

http 19624 13506

14050949 2017293

0 0

<output omitted>


Steps for Configuring NBAR for Static Protocols

Required steps:

1. Enable NBAR Protocol Discovery.

2. Configure a traffic class.

3. Configure a traffic policy.

4. Attach the traffic policy to an interface.

5. Enable PDLM if needed.


Configuring NBAR for Static Protocols Commands

Configures the match criteria for a class map on the basis of the specified protocol using the MQC configuration mode.

Static protocols are recognized based on the well-known destination port number.

A match not command can be used to specify a QoS policy value that is not used as a match criterion; in this case, all other values of that QoS policy become successful match criteria.

match protocol protocol

router(config-cmap)#


Configuring NBAR Example

HTTP is a static protocol using a well-known port number 80. However, other port numbers may also be in use.

The ip nbar port-map command will inform the router that other ports are also used for HTTP.


Steps for Configuring Stateful NBAR for Dynamic Protocols

Required steps:

1. Configure a traffic class.

2. Configure a traffic policy.

3. Attach the traffic policy to an interface.


Enhanced NBAR Classification for HTTP

Recognizes the HTTP GET packets containing the URL, and then matches all packets that are part of the HTTP GET request

Include only the portion of the URL following the address or host name in the match statement

match protocol http url url-string


match protocol http host hostname-string


Performs a regular expression match on the host field content inside an HTTP GET packet and classifies all packets from that host


match protocol http mime MIME-type


match protocol fasttrack file-transfer

regular-expression


Special NBAR Configuration for HTTP and FastTrack

Matches a packet containing the MIME type and all subsequent packets until the next HTTP transaction for stateful protocol.

Stateful mechanism to identify a group of peer-to-peer file-sharing applications.

Applications that use FastTrack peer-to-peer protocol include Kazaa, Grokster, Gnutella, and Morpheus.

A Cisco IOS regular expression is used to identify specific FastTrack traffic.

To specify that all FastTrack traffic will be identified by the traffic class, use asterisk (*) as the regular expression.


URL or HOST Specification String Options

Options Description

* Match any zero or more characters in this

position.

? Match any one character in this position.

| Match one of a choice of characters.

(|) Match one of a choice of characters in a

range. For example, xyz.(gif | jpg)

matches either xyz.gif or xyz.jpg.

[ ] Match any character in the range

specified, or one of the special

characters. For example, [0-9] is all of

the digits; [*] is the "*" character, and

[[] is the "[" character.


match protocol rtp [audio | video | payload-type

payload-string]


Configuring Stateful NBAR for RTP

Identifies real-time audio and video traffic in the class-map mode of MQC

Differentiates on the basis of audio and video codecs

The match protocol rtp command has these options:

audio: Match by payload type values 0 to 23, reserved for audio traffic

video: Match by payload type values 24 to 33, reserved for video traffic

payload-type: Match by a specific payload type value; provides more granularity than the audio or video options


Classification of RTP Session


Resources

Network-Based Application Recognition, Q&A

http://www.cisco.com/en/US/partner/products/ps6616/products_qanda_item09186a00800a3ded.shtml

Network-Based Application Recognition and Distributed Network-Based Application Recognition

http://www.cisco.com/en/US/partner/products/ps6350/products_configuration_guide_chapter09186a0080455985.html

Remaining percent calculations example

https://supportforums.cisco.com/thread/122893?tstart=0





https://supportforums.cisco.com/thread/122893?tstart=0


Introducing Queuing Implementations


Objectives

Describe the common causes of congestion on a link.

Compare and contrast various queuing methods used to relieve congestion.

Describe the purpose and functionality of software queues.

Describe the function and purpose of the hardware queue.


Congestion can occur at any point in the network where there are points of speed mismatches or aggregation.

Queuing manages congestion to provide bandwidth and delayguarantees.

Congestion and Queuing


• Speed mismatches are the most typical cause of congestion.

• Possibly persistent when going from LAN to WAN.

• Usually transient when going from LAN to LAN.

Speed Mismatch


Aggregation


What is Queuing?

Queuing is a congestion-management mechanism that allows you to control congestion on interfaces.

Queuing is designed to accommodate temporary congestion on an interface of a network device by storing excess packets in buffers until bandwidth becomes available.


Congestion and Queuing

.


Queuing Algorithms

First-in, first-out (FIFO)

Priority queuing (PQ)

Round robin

Weighted round robin (WRR)


FIFO

First packet in is first packet out

Simplest of all

One queue

All individual queues are FIFO

By default serial interfaces at E1 and below use WFQ, all others interfaces by default use FIFO.


Priority Queuing

Uses multiple queues

Allows prioritization

Always empties first queue before going to the next queue:

Empty queue number 1.

If queue number 1 is empty, then dispatch one packet from queue number 2.

If both queue number 1 and queue number 2 are empty, then dispatch one packet from queue number 3.

Queues number 2 and number 3 may ―starve‖

Best suited to low-bandwidth, congested serial interfaces


Round Robin Queuing

Uses multiple queues

No prioritization

Dispatches one packet from each queue in each round:

• One packet from queue number 1



Then repeat


Weighted Round Robin Queuing

Allows prioritization

Assign a weight to each queue

Dispatches packets from each queue proportionately to an assigned weight:

Dispatch up to four from queue number 1.

Dispatch up to two from queue number 2.

Dispatch 1 from queue number 3.

Go back to queue number 1.

Cisco CQ uses number of bytes instead of number of packets


Problems with Weighted Round Robin Queuing

Problem with WRR:

Some implementations of WRR dispatch a configurable number of bytes (threshold) from each queue for each round—several packets can be sent in each turn.

The router is allowed to send the entire packet even if the sum of all bytes is more than the threshold.


Router Queuing Components

Each physical interface has a hardware and a software queuing system.


Hardware and Software Router Queuing Components

The hardware queuing system always uses FIFO queuing.

The software queuing system can be selected and configured depending on the platform and Cisco IOS version.


The Software Queue

Generally, a full hardware queue indicates interface congestion, and software queuing is used to manage it.

When a packet is being forwarded, the router will bypass the software queue if the hardware queue has space in it(no congestion).


The Hardware Queue Routers determine the length of the hardware queue based

on the configured bandwidth of the interface.

The length of the hardware queue can be adjusted with the tx-ring-limit command.

Reducing the size of the hardware queue has two benefits:

It reduces the maximum amount of time that packets wait in the FIFO queue before being transmitted.

It accelerates the use of QoS in Cisco IOS software.

Improper tuning of the hardware queue may produce undesirable results:

A long transmit queue may result in poor performance of the software queuing system.

A short transmit queue may result in a large number of interrupts, which causes high CPU utilization and low link utilization.


R1#show controllers serial 0/1/0

Interface Serial0/1/0

Hardware is GT96K

DCE V.11 (X.21), clock rate 384000

<...part of the output omitted...>

1 sdma_rx_reserr, 0 sdma_tx_reserr

0 rx_bogus_pkts, rx_bogus_flag FALSE

0 sdma_tx_ur_processed

tx_limited = 1(2), errata19 count1 - 0, count2 - 0

Receive Ring

rxr head (27)(0x075BD090), rxr tail (0)(0x075BCEE0)

rmd(75BCEE0): nbd 75BCEF0 cmd_sts 80800000 buf_sz 06000000

buf_ptr 75CB8E0

rmd(75BCEF0): nbd 75BCF00 cmd_sts 80800000 buf_sz 06000000

buf_ptr 75CCC00

<...rest of the output omitted...>

Monitoring Hardware Queue Transmit Queue Length

The show controllers serial 0/1/0 command shows the length of the hardware queue.


Congestion on Software Interfaces

Subinterfaces and software interfaces (dialers, tunnels, Frame Relay subinterfaces) do not have their own

separate transmit queue.

Subinterfaces and software interfaces congest when

the transmit queue of their main hardware interface congests.

The tx-ring state (full, not-full) is an indication of hardware interface congestion.

The terms ―TxQ‖ and ―tx-ring‖ both describe the hardware queue and are interchangeable.


Self Check

1. When does the router use a software queue?

2. What are the typical causes of congestion?

3. When would FIFO queuing be appropriate in a network?

4. What is the ―worst case scenario‖ for Priority Queuing (PQ)?

5. How does Weighted Round Robin (WRR) improve on Round Robin queuing?


Summary

Speed mismatch and aggregation are the most common causes of congestion on a network link.

When network links experience congestion, queuing methods can be used to sort the traffic and then determine some method of prioritizing it onto an output link. Each queuing algorithm was designed to solve a specific network traffic problem and has a particular effect on network performance.

Software queuing is activated when the hardware queue fills. If the hardware queue is not full, software queuing is bypassed and packets are sent directly to the hardware output queue.


Q and A


Resources

Congestion Management Overview

http://www.cisco.com/en/US/partner/products/ps6350/products_configuration_guide_chapter09186a00800b75a9.html



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