OPNET-Chapter 4 - Switched LANs Networks

OPNET IT Guru Academic Edition

Chapter 4 LAB 3 – Switched LANs

‍N. Abedpoor‍

Imam Reza International University of Mashhad‍

N. Abedpoor – International Imam Reza University of Mashhad Dec. 2013

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● Building Network Topologies

• Steps for Building a Network Topology

• Examples of Various Topologies Used for Different

Studies

● Lab 3 – Switched LANs

Chapter 4 Lab3 – Switched LANs

N. Abedpoor – International Imam Reza University of Mashhad Dec. 2013 2

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● The software supports many different techniques for building

network topologies. Topologies can be created manually or

imported from tools that perform auto-discovery. The model

library that comes with the software provides models of

various devices used in current day networks. Devices that

aggregate sections of the network (such as LAN segments,

ATM/Frame Relay clouds) are provided in order to simplify the

network topology and improve simulation performance.

● using the software to do the following:

• build complete network topologies

• build partial topologies

• model a single path between two devices

Building Network Topologies using OPNET


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● There are five basic steps outlined for building a network

topology.

Steps for Building a Network Topology


Determine your eventual goal

Assess your existing network

Determine if you need aggregation

Select a building technique

Create your

network

topology

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● The choice of devices for constructing a network topology and

the method is very much a function of the goal of a simulation

study. Depending upon the context in which the software is

being used, you may represent the topology as a single path

between two devices, a partial topology with portions of the

network abstracted or a complete topology with every device

explicitly modeled.




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● only the infrastructure supporting traffic between two devices

of interest is represented

• For example, if the objective of using the software is to

analyze a client-server application

● The advantage of this topology is that it enhances the focus

of the study to the main objects of interest, i.e. the client and

the server. Since other devices are not explicitly modeled, the

simulation is very efficient. There is no loss of accuracy since

the effect of the remaining network on the client-server traffic

is taken into account. You can easily and quickly perform a

number of what-if scenarios by changing client/server

parameters or the amount of traffic in the intermediate

sections of the network.

Single Path



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● In certain situations, it may be important to represent portions

of the network in detail while abstracting other sections.

● For example, if the objective is to study the utilization of a

backbone, the backbone portion must be completely

represented. Other sections of the network may be abstracted.

However their effects should be captured when traffic

information is entered.

Partial Topology



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● A complete topology is necessary when a particular problem is

scaled across the network and it is important to identify the

impact of the problem on all devices involved.

● For example, if a new application is being deployed and the

objective of the simulation is to determine its impact on

intermediate network devices, it may be important to model

the complete topology.

● Complete topologies may also be used when the objective of

the study is to move a server to various prospective locations

and study the impact of each choice on network resources

(say link utilization).

Complete Topology



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● Listed below are some examples of goals and recommended

topologies:



Recommended Topology Goals of the simulation

Single Path Performance of a database application

Single Path Performance of FTP with different TCP settings

Single Path Performance of application for remote users

Single Path Performance of a new application in the network

Complete Effect of a new application deployment on the network

Partial Backbone analysis

Partial Trading off Fast Ethernet VS. Gigabit Ethernet

Partial Moving from shared media to a switched network

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● Before beginning construction the final topology, it is important to

have a complete picture of the existing network in the form of a

drawing or a map. It is important to identify all existing devices, their role, and the protocols that are running in the existing network. It is

also important to identify the flows and traffic patterns in your

existing network.

● Consider the following questions:

• 1. Is the network flat (predominantly switched) or segmented

(routed)?

• 2. Where are the main servers located (WWW server, database

server etc.)?

• 3. What is the main traffic flow (users accessing the database

server, traffic through a firewall etc.)?

• 4. What are the sources of broadcast and multicast traffic?




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● Before performing the final steps in generating a topology, it is

important to determine if you can aggregate portions of the network.

● Aggregation can be performed at the segment level (LAN segment)

or at the subnet level (IP subnet).

● Portions of the network, which are outside the corporate control such

as the Internet or the carriers, can also be represented as simple

"cloud" objects with the appropriate latencies.

● Examples of the above are illustrated graphically next slides:




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● A LAN segment can be aggregated into a shared LAN object. The

number of workstations that the shared LAN represents and the

different applications generating traffic can be specified. The shared

LAN automatically scales the traffic based on the number of stations.

Utilization measured on the shared LAN can be modeled as

background utilization on the shared LAN object.

Figure 1: Shared LAN Aggregation



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● Shared LAN segments connected to a switch may be aggregated into

a switched LAN object. The number of workstations that the entire

switched LAN segment represents can be specified. Applications can be

configured on the switched LAN and the model automatically scales the

total traffic based on the number of workstations. Utilization measured on

a switched segment can be input as background utilization on the

switched LAN. The switching speed for the LAN segment can also be

specified.

Figure 2: Shared LAN Aggregation



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● The frame relay cloud can be used to represent a section of the

core frame relay network. Typically, a company uses a frame relay

carrier service for long haul communications and the carrier

infrastructure can be represented as the frame relay cloud. Packet

latency and discard probabilities can be modeled on the frame relay

cloud. Similarly, an ATM cloud can be used to represent core portions

of an ATM network and an IP cloud can be used to represent portions

of the Internet.

Figure 3: Frame relay (or ATM) aggregation



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Figure 4: IP Level aggregation



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● Topologies can be created manually or automatically through a

process of importing from tools that perform auto-discovery.

● Topologies can be constructed automatically from router configuration files and text/XML files as well.

Each one of these techniques is discussed in detail below.

● Direct Import

● The software supports importing topologies directly from a number of

vendor products. Each import procedure varies slightly based on the

information obtained from the vendor products. Refer to the product

documentation for details on the import procedure.

Select a technique for creating the topology


Select a building

technique

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• The VNE Server Environment

The OPNET VNE (Virtual Network Environment) Server product

provides an on-line, continuously valid, integrated view of your network.

VNE Server collects network data from disparate sources, and

intelligently merges this information to create a unified network

representation that can be used for network planning, engineering, and

operations.

Designed for openness, VNE Server is a user-extensible solution that

can encompass virtually any data source. VNE Server provides a

complete, architected approach for managing network information.

• Vendor Products

You can import from vendor products such as HP Network Node

Manager or Tivoli Netview. Refer to the product documentation for the

complete list of supported vendor products and procedures on how to

import from these products.


Select a building

technique

‍

• Text/XML Files

OPNET supports text-based or XML-based topology import. These

text/XML files have a specific format that can be found in the product

documentation. Geographic location information can be supplied in

these files.

• Router Configurations

OPNET supports import of router configuration files. Geographic location

information can be supplied with the router configurations. When you

use router configuration files, the topology that is created will have

attributes that control routing behavior specified based on the contents

of the router configuration files.


Select a building

technique

‍

The key features of the import process:

● The import preserves the network layout and hierarchy. The

relative positioning of objects is preserved. If objects are within subnets, the software will create subnets and place objects within them.

● Devices are mapped accurately to the model library. The software maintains a large database of device models (e.g. routers, switches, servers etc.) and their characteristics. During import, devices are identified based on their function and vendor.

● Import provides aggregation. The topology can be imported with LAN level aggregation, IP segment level aggregation or no aggregation at all.

● A Question/Answer database provides a method for dealing with unmanaged devices in case of import from HP Network Node Manager.

● Import can repair structural defects in the network.


Select a building

technique

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● Manual Construction

● Manual construction can be used when the topology is simple (in

terms of number of objects and complexity of interconnection) or

when supporting tools that provide topology information for direct

import are not available.

● To build topologies by hand, the software provides a number of

object palettes that contain common network devices and links used

for interconnection. The software also provides a technique called

"Rapid Configuration" that allows you to quickly create standard

topologies (star, tree, bus, mesh, etc.) containing many devices with

a few clicks. Once a topology has been created by hand, the

software provides features that allow the user to select a large

number of objects and apply attribute values in one operation.

Consistency checking is provided to ensure that links are accurate

and the interconnected devices are compatible.


Select a building

technique

‍

● Once the steps above have been completed, you can build

the network topology.

● The link consistency check must be executed to ensure that

the topology is accurate and there are no disconnected links.

● When the topology construction is complete, you can specify

attribute values on devices and run simulations. Some

features that are useful for this purpose are listed below.


Create the

topology

Create the Topology

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Details about these features may be found in the

software documentation.

● Find node: Allows the user to locate any node by name across the

network. LAN objects or any objects that represent many devices can

be configured with the names of individual members that they

represent (aliases). The find node utility also locates a device by its

alias.

● Logical object selection: Objects can be selected based on their

type or any of their attribute settings. Selection sets can be retained

for further selection.

● Applying changes to selected objects: Changes to attribute values

for objects selected manually or using the find/logical object selection

command can be applied with a single click.


Create the

topology

‍

Details about these features may be found in the

software documentation.

● Configuring attributes: Attributes can be configured to represent

characteristics of the device. Protocol parameters can also be tuned.

● Selecting advanced models that contain many attributes: Models

are divided into a three-tier structure: advanced, intermediate and

final. Advanced models contain numerous attributes that can be

tuned based on the different protocols they contain. Intermediate

models contain a subset of the advanced model attributes and Final

models contain only very basic attributes that have to be configured

by the user.


Create the

topology

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● The example topology selected consists of users on shared LAN segments.

LAN segments on the same floor of an office are connected to each other via

a switch. All switches interface to a building router. A backbone spans various

campuses and connects the building routers together. Servers are located on

a server farm in one of the buildings.

Examples of Various Topologies


Co

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lete

To

po

log

y

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● If the network is being used to study the performance of an existing

application in the presence of regular day-to-day network traffic, a

single path from the client to the server may be adequate. The effect

of network traffic is to cause additional delay for the application

traffic. The network traffic is represented by background utilization on

the intermediate devices. Application traffic is modeled explicitly. This

is an example of a hybrid simulation. Hybrid simulation explicitly

models the application of interest. The network traffic effects are

analytically represented to obtain both accuracy and simulation

efficiency.

Topology for Client/Server Performance Analysis


Single Path Topology

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● If the network is used to study application deployment, it is

important to represent all the traffic flows from all clients to the

servers. Since the objective is to study application response

time and the effect of this application on the switches and

routers, it is not important to model in full detail of each LAN

segment. LANs may be aggregated into shared LAN objects

with the appropriate number of workstations. Note that the

LAN object will automatically scale the traffic based on the

number of workstations. The flows across the switches and

routers must be modeled explicitly as the effect of the new

application on such devices is important in the study.

Topology for Application Deployment


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Topology for Application Deployment


Partial Topology

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● If the above network is used to study utilization on the backbone, it is

important to model flows across the backbone accurately. Modeling

individual LAN segments and switches is not important. The shared

LAN segments along with the switches can be aggregated into

switched LAN segments that generate cross traffic via the backbone.

Topology for Analysis Backbone


Partial Topology

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● There is a limit to how many hosts can be attached to a single

network and to the size of a geographic area that a single

network can serve. Computer networks use switches to

enable the communication between one host and another,

even when no direct connection exists between those hosts.

● A switch is a device with several inputs and outputs leading to

and from the hosts that the switch interconnects. The core job

of a switch is to take packets that arrive on an input and

forward (or switch) them to the right output so that they will

reach their appropriate destination.

Lab 3 – Switched LANs


A Set of Local Area Networks Interconnected by Switches

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● A key problem that a switch must deal with is the finite

bandwidth of its outputs. If packets destined for a certain

output arrive at a switch and their arrival rate exceeds the

capacity of that output, then we have a problem of contention.

In this case, the switch will queue, or buffer, packets until the

contention subsides. If it lasts too long, however, the switch

will run out of buffer space and be forced to discard packets.

When packets are discarded too frequently, the switch is said

to be congested.

Lab 3 – Switched LANs


A Set of Local Area Networks Interconnected by Switches

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NOTES:

Create Project:

● Name the project <your initials>_SwitchedLAN

● Name the scenario OnlyHub

● make sure that Create Empty Scenario

● Choose Office for Network Scale


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NOTES:

Create the Network: ● Use Rapid Configuration.

● Star Topology

● Choose Ethernet from Model List


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● Save Project


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NOTES:

Configure Network Nodes

● Select Similar Nodes

● Edit Attributes.

● Set Value Shown in

figure.


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NOTES:

Choose Statistics

● Choose Individual Statistics

● choose the following four

statistics


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NOTES:

Configure the Simulation


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NOTES:

Duplicate Scenario

● We need to create another network that utilizes a switch and

see how this will affect the performance of the network.

● 1- Scenarios menu Duplicate Scenario name

HubAndSwitch OK

● 2- Open the Object Palette

● 3- place a Hub and a Switch to new scenario.


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NOTES:

● 4- change the name attribute of both models to Hub2 and

Switch

● Reconfigure the

network of HubAndSwitch


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NOTES:

Run the Simulation

● Scenarios menu Manage Scenario.

● Value under Results column to <collect>

● OK (to run Simulation)

● After simulation completes, click close

● Save your Project


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NOTES:

View the Results

● 1- Result menu Compare Results

● 2- Select and change something you see in figure


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NOTES:

View the Results

● Traffic Sent (packets/sec)


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NOTES:

View the Results

● Traffic Received(packets/sec)


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NOTES:

View the Results

● Collision Count


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Time to Believe yourself !!!

Start as professionals…


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OPNET-Chapter 4 - Switched LANs Networks