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Showing posts with label Networking Tutorial. Show all posts
Showing posts with label Networking Tutorial. Show all posts

Networking Terminologies

Please write a brief note on all the terminologies. A quiz will be taken on the following in the upcoming class.

Unshielded Twisted Pair Cables (UTP).
T568-A color Schemes for Straight Through, Cross Over, Roll Over Cables.
T568-B color Schemes for Straight Through, Cross Over, Roll Over Cables.

Network congestion
TCP congestion-avoidance
Additive increase/multiplicative decrease
Fast Retransmit and Fast Recovery

FireWall and VPNs
IP Tunnel
Asynchronous Transfer Mode (ATM):-
             Try to cover all the terminologies used in the following tutorial. ATM Tutorial     

Simulator class in NS2
Networking Nodes in NS2 and their features
Types of links available for us to use in NS2
Latency Time
Queueing Algorithms
TCP Sink Agent
NULL Agent

Paper Pattern:

Q1. Theoretical Portion as defined above. Prepare comprehensively.
Q2. NS2 complete. Prepare thoroughly. You will have to write code.
Q3. Do prepare thoroughly for RiverBed. You will have to perform task on riverbed. Following tasks are excluded.

A Shared media network
A direct link network
Small office network

Xgraph in NS2


One part of the ns-allinone package is 'xgraph', a plotting program which can be used to create graphic representations of simulation results. In this section, I will show you a simple way how you can create output files in your Tcl scripts which can be used as data sets for xgraph. On the way there, I will also show you how to use traffic generators.
A note: The technique I present here is one of many possible ways to create output files suitable for xgraph. If you think there is a technique which is superior in terms of understandablity (which is what I aim for in this tutorial), please let me know.

First of all, we create the following topology:
Nam snap shot
The following piece of code should look familiar to you by now if you read the first sections of this tutorial.

set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]
set n4 [$ns node]

$ns duplex-link $n0 $n3 1Mb 100ms DropTail
$ns duplex-link $n1 $n3 1Mb 100ms DropTail
$ns duplex-link $n2 $n3 1Mb 100ms DropTail
$ns duplex-link $n3 $n4 1Mb 100ms DropTail

Dynamic Nodes generation and traffic flow in ns2

Here is the code for dynamically creating nodes and create traffic flow dynamically using protocol.

#Create a simulator object
set ns [new Simulator]

#Tell the simulator to use dynamic routing
$ns rtproto DV

#Open the nam trace file
set nf [open out.nam w]
$ns namtrace-all $nf

#Define a 'finish' procedure
proc finish {} {
        global ns nf
        $ns flush-trace
#Close the trace file
        close $nf
#Execute nam on the trace file
        exec nam out.nam &
        exit 0

#Create seven nodes
for {set i 0} {$i < 7} {incr i} {
        set n($i) [$ns node]

#Create links between the nodes
for {set i 0} {$i < 7} {incr i} {
        $ns duplex-link $n($i) $n([expr ($i+1)%7]) 1Mb 10ms DropTail

#Create a UDP agent and attach it to node n(0)
set udp0 [new Agent/UDP]
$ns attach-agent $n(0) $udp0

# Create a CBR traffic source and attach it to udp0
set cbr0 [new Application/Traffic/CBR]
$cbr0 set packetSize_ 500
$cbr0 set interval_ 0.005
$cbr0 attach-agent $udp0

NS2 and UBUNTU Installation on VMWARE

There are multiple ways that you can adopt to install ns2. As ns2 runs on the linux. so first you will have to install linux. You can install any distribution of linux fedora, ubuntu etc.

So, one way to do the installation is to first install this software called VMWARE. It creates a virtual machine which allows you to run operating system on another operating system just like any other application. Other ways include by installing Ubuntu direct from website using windows installer. Lets look at the first option.

Install Vmware

Install fedora or any other Linux distribution on VMware. Select ‘New Virtual Machine’ option.


Click Next.

BroadCast and Collision domains

BroadCast Domain

A broadcast domain is a logical division of a computer network, in which all nodes can reach each other by broadcast at the data link layer. A broadcast domain can be within the same LAN segment or it can be bridged to other LAN segments. A broadcast domain encompasses a set of devices for  when one of the devices sends a broadcast, all the other devices receive a copy of the broadcast. For example, switches flood broadcasts and multicasts on all ports. Because broadcast frames are sent out all ports, a switch creates a single broadcast domain.
Any computer connected to the same repeater or switch is a member of the same broadcast domain. Further, any computer connected to the same set of inter-connected switches/repeaters is a member of the same broadcast domain. Routers and other higher-layer devices form boundaries between broadcast domains.
This is as compared to a collision domain, which would be all nodes on the same set of inter-connected repeaters, divided by switches and learning bridges. Collision domains are generally smaller than broadcast domains. Broadcast domains are only divided by layer 3 network devices such as routers or layer 3 switches. However,some layer two network devices are also able to divide the collision domains. A broadcast domain is a set of NICs for which a broadcast frame sent by one NIC is received by all other NICs in the same broadcast domain 

Collision Domain

A collision domain is the set of LAN interfaces whose frames could collide with each other, but not with frames sent by any other devices in the network. The collision is happened when to computer in same time want to use bandwidth. The CSMA/CD algorithm that deals with the issue of collisions, and some of the differences between how hubs and switches operate to create either a single collision domain (hubs) or many collision domains (switches). Generally speaking in easy terms, A collision domain is a set of network interface cards (NIC) for which a frame sent by one NIC could result in a collision with a frame sent by any other NIC in the same collision domain.
Only one device in the collision domain may transmit at any one time, and the other devices in the domain listen to the network in order to avoid data collisions. Because only one device may be transmitting at any one time, total network bandwidth is shared among all devices. Collisions also decrease network efficiency on a collision domain; if two devices transmit simultaneously, a collision occurs, and both devices must retransmit at a later time.
Modern wired networks use a network switch to eliminate collisions. By connecting each device directly to a port on the switch, either each port on a switch becomes its own collision domain (in the case of half duplex links) or the possibility of collisions is eliminated entirely in the case of full duplex links.
When creating any Ethernet LAN, you use some form of networking devices—typically switches today—a few routers, and possibly a few hubs. The different parts of an Ethernet LAN may behave differently, in terms of function and performance, depending on which types of devices are used. These differences then affect a network engineer’s decision when choosing how to design a LAN. The terms collision domain and broadcast domain define two important effects of the process of segmenting LANs using various devices. 

The Importance  of Collision and Broadcast Domains on LAN Design

When designing a LAN,  when choosing the number of devices in each collision domain and broadcast domain. First, consider the devices in a single collision domain for a moment. For a single collision domain: 
  1. The devices share the available bandwidth in network.
  2. The devices may inefficiently use that bandwidth due to the effects of collisions
For example, you might have ten PCs with 10/100 Ethernet NICs. If you connect all ten PCs to ten different ports on a single 100-Mbps hub, you have one collision domain, and the PCs in that collision domain share the 100 Mbps of bandwidth.
That may work well and meet the needs of those users. However, with higher traffic loads, the hub’s performance would be worse and you need a switch . Using a switch instead of a hub, with the same topology, would create ten different collision domains, each with 100 Mbps of bandwidth. Also, with only one device on each switch interface, no collisions would occur. This means that you could enable full duplex on each interface, effectively giving each interface 200 Mbps.
Using the switches instead of hubs seems like an obvious choice given the overwhelming performance benefits. Frankly, most new installations today use switches exclusively.


VLAN or  Virtual Local Area Network is a phenomenon which is used to logically separate or combine a network. It is used to configured one or more devices, so that they can communicate, as if they were attached to the same wire, when in fact they are located on a number of different LAN segments. Because VLANs are based on logical instead of physical connections, they are extremely flexible. 

What is VLAN

VLAN is a concept of partitioning of a physical network, so that distinct broadcast domains are created. This is usually achieved on switch or router devices. Simpler devices only support partitioning on a port level, so sharing VLANs across devices requires running dedicated cabling for each VLAN.
Grouping hosts with a common set of requirements regardless of their physical location by VLAN can greatly simplify network design. A VLAN has the same attributes as a physical local area network (LAN), but it allows for end stations to be grouped together more easily even if they are not on the same network switch. Without VLANs, a switch considers all interfaces on the switch to be in the same broadcast domain.To physically replicate the functions of a VLAN would require a separate, parallel collection of network cables and equipment separate from the primary network.

 How VLAN's work

When a LAN bridge receives data from a workstation, it tags the data with a VLAN identifier indicating the VLAN from which the data came. This is called explicit tagging. It is also possible to determine to which VLAN the data received belongs using implicit tagging. In implicit tagging the data is not tagged, but the VLAN from which the data came is determined based on other information like the port on which the data arrived. Tagging can be based on the port from which it came, the source Media Access Control (MAC) field, the source network address, or some other field or combination of fields. VLAN's are classified based on the method used. To be able to do the tagging of data using any of the methods, the bridge would have to keep an updated database containing a mapping between VLAN's and whichever field is used for tagging. For example, if tagging is by port, the database should indicate which ports belong to which VLAN. This database is called a filtering database. Bridges would have to be able to maintain this database and also to make sure that all the bridges on the LAN have the same information in each of their databases. The bridge determines where the data is to go next based on normal LAN operations. Once the bridge determines where the data is to go, it now needs to determine whether the VLAN identifier should be added to the data and sent. If the data is to go to a device that knows about VLAN implementation (VLAN-aware), the VLAN identifier is added to the data. If it is to go to a device that has no knowledge of VLAN implementation (VLAN-unaware), the bridge sends the data without the VLAN identifier.


Why use VLAN's?

VLAN offer a number of advantages over traditional LAN.

    Physical topology independence

    VLANs provide independence from the physical topology of the network by allowing physically diverse workgroups to be logically connected within a single broadcast domain. If the physical infrastructure is already in place, it now becomes a simple matter to add ports in new locations to existing VLANs if a department expands or relocates. These assignments can take place in advance of the move, and it is then a simple matter to move devices with their existing configurations from one location to another. The old ports can then be "decommissioned" for future use, or reused by the department for new users on the VLAN.

    In networks where traffic consists of a high percentage of broadcasts and multicasts, VLAN's can reduce the need to send such traffic to unnecessary destinations. For example, in a broadcast domain consisting of 10 users, if the broadcast traffic is intended only for 5 of the users, then placing those 5 users on a separate VLAN can reduce traffic.
    Compared to switches, routers require more processing of incoming traffic. As the volume of traffic passing through the routers increases, so does the latency in the routers, which results in reduced performance. The use of VLAN's reduces the number of routers needed, since VLAN's create broadcast domains using switches instead of routers. Switched networks by nature will increase performance over shared media devices in use today, primarily by reducing the size of collision domains. Grouping users into logical networks will also increase performance by limiting broadcast traffic to users performing similar functions or within individual workgroups. Additionally, less traffic will need to be routed, and the latency added by routers will be reduced

    Formation of Virtual Workgroups
    Nowadays, it is common to find cross-functional product development teams with members from different departments such as marketing, sales, accounting, and research. These workgroups are usually formed for a short period of time. During this period, communication between members of the workgroup will be high. To contain broadcasts and multicasts within the workgroup, a VLAN can be set up for them. With VLAN's it is easier to place members of a workgroup together. Without VLAN's, the only way this would be possible is to physically move all the members of the workgroup closer together.
    Despite this saving, VLAN's add a layer of administrative complexity, since it now becomes necessary to manage virtual workgroups.

    Reduced Cost
    VLAN's can be used to create broadcast domains which eliminate the need for expensive routers.

    Periodically, sensitive data may be broadcast on a network. In such cases, placing only those users who can have access to that data on a VLAN can reduce the chances of an outsider gaining access to the data. VLAN's can also be used to control broadcast domains, set up firewalls, restrict access, and inform the network manager of an intrusion.

    Improved manageability
    VLANs provide an easy, flexible, less costly way to modify logical groups in changing environments. VLANs make large networks more manageable by allowing centralized configuration of devices located in physically diverse locations.

Networking Cables and Connections

In order for the communication to take place, cables play important role. Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. The type of cable chosen for a network is related to the network's topology, protocol, and size.
There are various types of cables used in networks as follows.
  • Unshielded Twisted Pair (UTP) Cable
  • Shielded Twisted Pair (STP) Cable
  • Coaxial Cable
  • Fiber Optic Cable

Twisted Pair Cables:
Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs. In balanced pair operation, the two wires carry equal and opposite signals and the destination detects the difference between the two. This is known as differential mode transmission. Noise sources introduce signals into the wires by coupling of electric or magnetic fields and tend to couple to both wires equally. The noise thus produces a common-mode signal which is cancelled at the receiver when the difference signal is taken.

Categories Of UTP Cable:
It has been categorized into three categories based on the equipment that are being connected through these wires.
i. Straight Through Cable
ii. Cross Over Cable
iii. Roll Over Cable


Straight Through Cable:
Straight through cables are used to connect different devices like Switch to PC. Switch to Router. Router to Switch etc. Straight-through cables are used when each end of the communication transmits and receives on different pairs.

Cross Over Cable:
In a cross over the cable, the send and receive wires are "crossed over", meaning the wires are opposite on each end. This allows two PCs to talk to each other, has it connects the send of one computer to the receive of the other. Hence, the cross over cables are used to connect similar devices like PC to PC , Router to Router, Switch to Switch, Hub to Hub etc.

Roll Over Cable:
Roll over cables are used to connect to the console port of the device. It gets the name rollover because the pin outs on one end are reversed from the other, as if the wire had been rolled over and you were viewing it from the other side.

Transmission Pins:
Devices that transmit on 1,2 and receive on 3,6
1) PC
3)Wireless Access Point AP
4) Networked printers
Devices that transmit on 3,6 and receive on 1,2


Required Equipment:
In order to make a network cable you need the following equipment.
i. Cat5, Cat5e cable.

CAT5 cable usually contains four pairs of copper wire, Fast Ethernet communications only utilize two pairs. A newer specification for CAT5 cable -CAT5 enhanced ("CAT5e" or "CAT 5e")- supports networking at Gigabit Ethernet[ speeds (up to 1000 Mbps) over short distances by utilizing all four wire pairs, and it is backward-compatible with ordinary CAT5.

ii. A connector named RJ-45.

RJ45 connectors feature eight pins to which the wire strands of a cable interface electrically. Standard RJ-45 pin outs define the arrangement of the individual wires needed when attaching connectors to a cable.

iii. Crimping tool:

Use to crimp the cable inside RJ 45 connector. 

iv. Wire stripper or Knife:

You can use a knife too to cut the wire open. In order to make different combinations of it. we will have to cut the upper protective coating and bring out the eight wires. 

Category Speed Use
1 1 Mbps Voice Only (Telephone Wire)
2 4 Mbps LocalTalk & Telephone (Rarely used)
3 16 Mbps 10BaseT Ethernet
4 20 Mbps Token Ring (Rarely used)
5 100 Mbps (2 pair) 100BaseT Ethernet
5e 1,000 Mbps Gigabit Ethernet
6 10,000 Mbps Gigabit Ethernet

Auto-MDIX (automatic medium-dependent interface crossover) is a computer networking technology that automatically detects the required cable connection type (straight-through or crossover) and configures the connection appropriately, thereby removing the need for crossover cables to interconnect switches or connecting PCs peer-to-peer. When it is enabled, either type of cable can be used and the interface automatically corrects any incorrect cabling. For Auto-MDIX to operate correctly, the speed on the interface and duplex setting must be set to "auto".

Networking Devices

Since, we are going to do a series of tutorials on packet tracer. In this manner, we need to have a familiarity of various networking components and devices. We are going to discuss some important devices which are going to be used in networking. 

All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers etc. These devices also need cables to connect them. In this tutorial, we are going to discuss these important devices.  

 Network interface cards

A NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or wirelessly.The NIC provides the transfer of data in  megabytes. 


Every device on a network that needs to transmit and receive data must have a network interface card (NIC) installed. They are sometimes called network adapters, and are usually installed into one of the computer's expansion slots in the same way as a sound or graphics card. The NIC includes a transceiver, (a transmitter and receiver combined). The transceiver allows a network device to transmit and receive data via the transmission medium. Each NIC has a unique 48-bit Media Access Control (MAC) address burned in to its ROM during manufacture. The first 24 bits make up a block code known as the Organisationally Unique Identifier (OUI) that is issued to manufacturers of NICs, and identify the manufacturer. The issue of OUIs to organisations is administered by the Institute of Electrical and Electronics Engineers (IEEE). The last 24 bits constitute a sequential number issued by the manufacturer. The MAC address is sometimes called a hardware address or physical address, and uniquely identifies the network adapter. It is used by many data link layer communications protocols, including Ethernet, the 802.11 wireless protocol and Bluetooth. The use of a 48-bit adress allows for 248(281,474,976,710,656) unique addresses. A MAC address is usually shown in hexadecimal format, with each octet separated by a dash or colon, 

For example: 00-60-55-93-R2-N7


A repeater is an electronic device that receives a signal and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair ethernet configurations, repeaters are required for cable runs longer than 100 meters away from the computer. As signals travel along a transmission medium there will be a loss of signal strength i.e. attenuation. A repeater is a non-intelligent network device that receives a signal on one of its ports, regenerates the signal, and then retransmits the signal on all of its remaining ports. Repeaters can extend the length of a network (but not the capacity) by connecting two network segments. Repeaters cannot be used to extend a network beyond the limitations of its underlying architecture, or to connect network segments that use different network access methods. They can, however, connect different media types, and may be able to link bridge segments with different data rates. 

Repeaters are used to boost signals in coaxial and twisted pair cable and in optical fibre lines. An electrical signal in a cable gets weaker the further it travels, due to energy dissipated in conductor resistance and dielectric losses. Similarly a light signal traveling through an optical fiber suffers attenuation due to scattering and absorption. In long cable runs, repeaters are used to periodically regenerate and strengthen the signal. 


A hub contains multiple ports. When a packet arrives at one port, it is copied to all the ports of the hub for transmission. In a hub, a frame is passed along or "broadcast" to every one of its ports. It doesn't matter that the frame is only destined for one port. The hub has no way of distinguishing which port a frame should be sent to. Passing it along to every port ensures that it will reach its intended destination. This places a lot of traffic on the network and can lead to poor network response times. Additionally, a 10/100Mbps hub must share its bandwidth with each and every one of its ports. So when only one PC is broadcasting, it will have access to the maximum available bandwidth. If, however, multiple PCs are broadcasting, then that bandwidth will need to be divided among all of those systems, which will degrade performance.

Network Hub


A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges do not copy traffic to all ports, as hubs do, but learn which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.

Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.

Network Bridge
Bridges don't know anything about protocols, but just forward data depending on the destination address in the data packet. This address is not the IP address, but the MAC (Media Access Control) address that is unique to each network adapter card. The bridge is basically just to connect two local-area networks (LANs), or two segments of the same LAN that use the same protocol. Bridges can extend the length of a network, but unlike repeaters they can also extend the capacity of a network, since each port on a bridge has its own MAC address. When bridges are powered on in an Ethernet network, they start to learn the network's topology by analysing the source addresses of incoming frames from all attached network segments (a process called backward learning ). Over a period of time, they build up a routing table . 

The bridge monitors all traffic on the segments it connects, and checks the source and destination address of each frame against its routing table. When the bridge first becomes operational, the routing table is blank, but as data is transmitted back and forth, the bridge adds the source MAC address of any incoming frame to the routing table and associates the address with the port on which the frame arrives. In this way, the bridge quickly builds up a complete picture of the network topology. If the bridge does not know the destination segment for an incoming frame, it will forward the frame to all attached segments except the segment on which the frame was transmitted. Bridges reduce the amount of traffic on individual segments by acting as a filter, isolating intra-segment traffic. This can greatly improve response times.


The switch is a relatively new network device that has replaced both hubs and bridges in LANs. A switch uses an internal address table to route incoming data frames via the port associated with their destination MAC address. Switches can be used to connect together a number of end-user devices such as workstations, or to interconnect multiple network segments. A switch that interconnects end-user devices is often called a workgroup switch. Switches provide dedicated full-duplex links for every possible pairing of ports, effectively giving each attached device its own network segment This significantly reduces the number of intra-segment and inter-segment collisions. Strictly speaking, a switch is not capable of routing traffic based on IP address (layer 3) which is necessary for communicating between network segments or within a large or complex LAN. Some switches are capable of routing based on IP addresses but are still called switches as a marketing term. A switch normally has numerous ports, with the intention being that most or all of the network is connected directly to the switch, or another switch that is in turn connected to a switch.

Network Switch


Routers are networking devices that forward data packets between networks using headers and forwarding tables to determine the best path to forward the packets. A network environment that consists of several interconnected networks employing different network protocols and architectures requires a sophisticated device to manage the flow of traffic between these diverse networks. Such a device, sometimes referred to as an intermediate system, but more commonly called a router, must be able to determine how to get incoming packets (or datagrams) to the destination network by the most efficient route. Routers gather information about the networks to which they are connected, and can share this information with routers on other networks. The information gathered is stored in the router's internal routing table, and includes both the routing information itself and the current status of various network links. Routers exchange this routing information using special routing protocols. 

A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Routers are located at gateways, the places where two or more networks connect, and are the critical device that keeps data flowing between networks and keeps the networks connected to the Internet. When data is sent between locations on one network or from one network to a second network the data is always seen and directed to the correct location by the router. The router accomplishes this by using headers and forwarding tables to determine the best path for forwarding the data packets, and they also use protocols such as ICMP to communicate with each other and configure the best route between any two hosts. The Internet itself is a global network connecting millions of computers and smaller networks. There are various routing protocols which are helpful for various different environments and will be discussed later.