Accessing the WAN – Chapter 8 ppsx

Documenting Your Network ƒ To efficiently diagnose and correct network problems, a network engineer needs to know network baseline.. Network Configuration Table –Contains up-to-date re

Accessing the WAN – Chapter 8

Objectives

– Establish and document a network baseline

– Describe the various troubleshooting methodologies and troubleshooting tools

– Describe the common issues that occur during WAN implementation

– Identify and troubleshoot common enterprise network implementation issues using a layered model approach

Documenting Your Network

ƒ To efficiently diagnose and correct network problems,

a network engineer needs to know network baseline

–This information is captured in documentation

ƒ Network documentation include 3 components:

1 Network configuration table

2 End-system configuration table

3 Network topology diagram

1 Network Configuration Table

–Contains up-to-date records of hardware and software

•Type of device, model designation

•IOS image name

•Device network hostname

•Location of the device (building, floor, room, rack, panel)

•If it is a modular device, include all module types and in which module slot they are located

•Data link layer addresses

•Network layer addresses

•Any additional important information about physical aspects

Documenting Your Network

2 End-system Configuration Table

–Contains baseline records used in end-system devices

such as servers, and desktop workstations

•Device name (purpose)

•Operating system and version

•IP address

•Subnet mask

•Default gateway, DNS server, and WINS server addresses

•Any high-bandwidth network applications that the system runs

end-3 Network Topology Diagram

–Graphical representation of a network, which illustrates

how each device in a network is connected and its

logical architecture

Network Documentation Process

ƒ When you document your network, you may have to

gather information directly from routers and switches

ƒ Commands that are useful to the network

documentation process include:

–The ping command is used to test connectivity with

neighboring devices Pinging to other PCs in the network

also initiates the MAC address auto-discovery process

–The telnet command is used to log in remotely to a

device for accessing configuration information

–The show ip interface brief is used to display the up

or down status and IP address of all interfaces

–The show ip route command is used to display the

routing table in a router to learn the directly connected

neighbors, more remote devices (through learned

routes), and the routing protocols

–The show cdp neighbor detail command is used to

obtain detailed information about directly connected

Cisco neighbor devices

Why is Establishing a Baseline Important?

ƒ Establishing a network performance baseline requires

collecting key performance data from the ports and

devices that are essential to network operation

–How does the network perform during a normal or

average day?

• Measuring the initial performance allows a network administrator to determine the difference between abnormal behavior and proper network performance

–Where are the underutilized and over-utilized areas?

• It may also reveal areas in the network that are underutilized and quite often can lead to network redesign efforts based on quality and capacity observations

–Where are the most errors occurring?

• In addition, analysis after an initial baseline tends to reveal hidden problems

Steps for Establishing a Network Baseline

3 steps for planning the first baseline:

ƒ Step 1 Determine what types of data to collect

–When conducting the initial baseline, start by selecting

a few variables that represent the defined policies If too

many data points are selected, the amount of data can

be overwhelming

• Generally, some good measures are interface utilization and CPU utilization

ƒ Step 2 Identify devices and ports of interest

– Devices and ports of interest include:

• Network device ports that connect to other network devices

• Servers

• Key users

• Anything else considered critical to operations

–By narrowing the ports polled, the results are concise,

and network management load is minimized

Steps for Establishing a Network Baseline

ƒ Step 3 Determine the baseline duration

–This period should be at least seven days to

capture any daily or weekly trends

–A baseline needs to last no more than six weeks

–Generally, a two-to-four-week baseline is

adequate

• The figure shows examples of several screenshots of CPU utilization trends captured over a daily, weekly, monthly, and yearly period

• The work week trends are too short to accurately reveal the recurring nature of the utilization surge that occurs every weekend when a database backup operation consumes network bandwidth

• The yearly trend shown in the example is too long

a duration to provide meaningful baseline performance details

–Baseline analysis of the network should be

conducted on a regular basis

Measuring Network Performance Data

ƒ Sophisticated network management software is

often used to baseline large networks

– For example, Fluke Network SuperAgent module

enables administrators to automatically create reports using Intelligent Baselines feature

• This feature compares current performance levels with historical observations and can automatically identify performance problems and applications that do not provide expected levels of service

ƒ In simpler networks, the baseline tasks may

require a combination of manual data collection

and simple network protocol inspectors

– Hand collection using show commands on

individual network devices is extremely time consuming and should be limited to mission- critical network devices

General Approach to Troubleshooting

ƒ Using efficient troubleshooting techniques shortens overall

troubleshooting time

ƒ Two extreme approaches to troubleshooting almost always result

in disappointment, delay, or failure

– At one extreme is the theorist, or rocket scientist, approach

• The rocket scientist analyzes and reanalyzes the situation until the exact cause at the root of the problem has been identified

• While this process is fairly reliable, few companies can afford to have their networks down for the hours or days

– At the other extreme is the impractical, or caveman, approach

• The caveman's first instinct is to start swapping cards, cables, and software until miraculously the network begins operating again

• This approach may achieve a change in symptoms faster, it is not reliable

ƒ the better approach is somewhere in the middle using elements

Using Layered Models for Troubleshooting

OSI Versus TCP/IP Layered Models

ƒ OSI Reference Model

–The upper layers (5-7) deal with application issues and

are implemented only in software

–The lower layers (1-4) handle data-transport issues

•Layers 3 and 4 are generally implemented only in software

•The physical layer (Layer 1) and data link layer (Layer 2) are implemented in hardware and software

ƒ TCP/IP Model

–The application layer in the TCP/IP suite actually

combines the functions of the three OSI model layers:

session, presentation, and application

–The transport layers of TCP/IP is responsible for

exchanging segments between devices

–The Internet layer is responsible for placing messages in

a fixed format that allows devices to handle them

–The network access layer communicates directly with

the network media and provides an interface between

the architecture of the network and the Internet layer

General Troubleshooting Procedures

ƒ The stages of the general troubleshooting process are:

–Stage 1 Gather symptoms - Troubleshooting begins with

the process of gathering and documenting symptoms from

the network, end systems, and users

•Symptoms may appear in many different forms, including alerts from the network management system, console messages, and user complaints

–Stage 2 Isolate the problem - The problem is not isolated

until a single problem, or a set of problems, is identified

–Stage 3 Correct the problem - Having isolated and

identified the cause of the problem, the network

administrator works to correct the problem by

implementing, testing, and documenting a solution

ƒ If the network administrator determines that the

corrective action has created another problem,

Troubleshooting Methods

ƒ There are three main methods for troubleshooting:

ƒ Bottom-Up Troubleshooting Method

–In bottom-up troubleshooting you start with the physical

components of the network and move up through the layers

•Bottom-up troubleshooting is a good approach to use when the problem is suspected to be a physical one

ƒ Top-Down Troubleshooting Method

–In top-down troubleshooting your start with the end-user

applications and move down the layers of the OSI model

•Use this approach for simpler problems or when you think the problem is with a piece of software

ƒ Divide-and-Conquer Troubleshooting Method

–In divide-and-conquer troubleshooting you start by collecting

user experience of the problem, document the symptoms

and then, using that information, make an informed guess as

to which OSI layer to start your investigation

•For example, if users can't access the web server and you can ping the server, then you know that the problem is above Layer 3

•If you can't ping the server, then you know the problem is likely at

a lower OSI layer

Guidelines for Selecting a Troubleshooting Method

ƒ To quickly resolve network problems,

take the time to select the most effective

troubleshooting method

–Use the process shown in the figure to

help you select the most efficient

troubleshooting method

ƒ For example: Two IP routers are not

exchanging routing information The last

time this type of problem occurred it was

a protocol issue So you choose the

divide-and-conquer troubleshooting

method

Gathering Symptoms

ƒ Step 1 Analyze existing symptoms

–Analyze symptoms gathered from the trouble ticket or

users to form a definition of the problem

ƒ Step 2 Determine ownership

–If problem is within your system, move onto next stage

–If the problem is outside the boundary of your control, for

example, lost Internet connectivity you need to contact

an administrator for the external system

ƒ Step 3 Narrow the scope

–Determine if the problem is at the core, distribution, or

access layer of the network

ƒ Step 4 Gather symptoms from suspect devices

–Use knowledge and experience to determine if the

problem is a hardware or software problem

ƒ Step 5 Document symptoms

–Sometimes the problem can be solved using the

documented symptoms If not, begin the isolating phase

of the general troubleshooting process

Gathering Symptoms

symptoms about the network

–Although the debug command is an

important tool for gathering symptoms it

generates a large amount of console

message traffic and the performance of a

network device can be noticeably affected

–Make sure you warn network users that a

troubleshooting effort is underway and that

network performance may be affected

–Remember to disable debugging when you

are done

Gathering Symptoms: Questioning End Users

may be experiencing, use effective questioning techniques

document the symptoms of a problem

end-user example questions

Software Troubleshooting Tools

ƒ NMS Tools

–Network management system (NMS) tools

include device-level monitoring, configuration,

and fault management tools

–Network monitoring software graphically

displays a physical view of network devices,

allowing network managers to monitor remote

devices without physically checking them

–Examples are CiscoView, HP Openview, Solar

Winds, and What's Up Gold

ƒ Knowledge Bases

–On-line network device vendor knowledge

bases have become indispensable sources of

Software Troubleshooting Tools

ƒ Baselining Tools

–For example they can help you draw network

diagrams, help you to keep network software and

hardware documentation up-to-date and help you to

cost-effectively measure baseline network bandwidth

use

–Many tools for automating the network

documentation and baselining process are available

–The figure shows a screen chapter of the SolarWinds

LAN surveyor and CyberGauge software

ƒ Protocol Analyzers

–A protocol analyzer decodes the various protocol

layers in a recorded frame and presents this

information in a relatively easy to use format

–The figure shows a screen capture of the Wireshark

protocol analyzer

–Most protocol analyzers can filter traffic that meets

certain criteria so that, for example, all traffic to and

from a particular device can be captured

Hardware Troubleshooting Tools

ƒ Network Analysis Module

–A network analysis module (NAM) can be

installed in Cisco Catalyst 6500 series switches

and Cisco 7600 series routers to provide a

graphical representation of traffic

ƒ Digital Multimeters

–Digital multimeters (DMMs) are test instruments

that are used to directly measure electrical values

of voltage, current, and resistance

ƒ Cable Testers

–Cabling testers can be used to detect broken

wires, crossed-over wiring, shorted connections,

and improperly paired connections

–These devices can be inexpensive continuity

Hardware Troubleshooting Tools

ƒ Cable Analyzers

–Cable analyzers are multifunctional handheld devices that

are used to test and certify copper and fiber cables for

different services and standards

–The more sophisticated tools include advanced

troubleshooting diagnostics that measure distance to

performance defect (NEXT, RL), identify corrective

actions, and graphically display crosstalk and impedance

behavior

ƒ Portable Network Analyzers

–Portable devices that are used for troubleshooting

switched networks and VLANs

–By plugging the network analyzer in anywhere on the

network, a network engineer can see the switch port to

which the device is connected and the average and peak

utilization

–The analyzer can also be used to discover VLAN

configuration, identify top network talkers, analyze

network traffic, and view interface details

Troubleshooting Tools: Research Activity

ƒ The following are links to various troubleshooting tools

WAN Communications

ƒ WAN technologies function at the lower three

layers of the OSI reference model

ƒ A communications provider normally owns the

data links that make up a WAN

–The links are made available to subscribers for a

fee and are used to interconnect LANs or connect

to remote networks

–WAN data transfer speed (bandwidth) is

considerably slower than the common LAN

bandwidth

–The charges for link provision are the major cost

element, therefore the WAN implementation must

aim to provide maximum bandwidth at acceptable

cost

Steps in WAN Design

these are the steps for designing or modifying a WAN:

ƒ Step 1 Locate LANs - Establish the source and destination

endpoints that will connect through the WAN

ƒ Step 2 Analyze traffic - Know what data traffic must be

carried, its origin, and its destination

ƒ Step 3 Plan the topology - A high requirement for availability

requires extra links that provide alternative data paths for

redundancy and load balancing

ƒ Step 4 Estimate the required bandwidth - Traffic on the links

may have varying requirements for latency and jitter

ƒ Step 5 Choose the WAN technology - Suitable link

technologies must be selected

WAN Traffic Considerations

ƒ The table in the figure shows

the wide variety of traffic

types and their varying

requirements of bandwidth,

latency, and jitter that WAN

links are required to carry

–To determine traffic flow

conditions and timing of a WAN

link, you need to analyze the

traffic characteristics specific to

each LAN that is connected to

the WAN

WAN Topology Considerations

ƒ Designing a WAN topology consists of the following:

– Selecting an interconnection pattern or layout for the links

between the various locations – Selecting the technologies for those links to meet the

enterprise requirements at an acceptable cost

• More links increase the cost of the network services, but having multiple paths between destinations increases reliability

• Adding more network devices to the data path increase latency and decreases reliability

ƒ Many WANs use a star topology

– As the enterprise grows and new branches are added, the

branches are connected back to the head office, producing a traditional star topology

ƒ Star endpoints are sometimes cross-connected, creating

WAN Topology Considerations - Hierarchical

ƒ When many locations must be joined, a hierarchical

solution is recommended

ƒ For example, imagine an enterprise that is

operational in every country of the European Union

and has a branch in every town with a population

over 10,000 Each branch has a LAN, and it has been

decided to interconnect the branches

–A mesh network is clearly not feasible because there

would be hundreds of thousands of links

–A three-layer hierarchy is often useful when the network

traffic mirrors the enterprise branch structure and is

divided into regions, areas, and branches

•Group the LANs in each area and interconnected them to form a region,

– The area could be based on the number of locations to be connected with an upper limit of between 30 and 50

– The area would have a star topology, with the hubs of the stars linked to form the region

•interconnect the regions to form the core of the WAN

– Regions could be geographic, connecting between three and 10 areas, and the hub of each region could be linked point-to-point