Archive for the ‘Theory’ Category
What is Packet Tracer?
Packet Tracer is a standalone, medium-fidelity, simulation-based learning environment for networking novices to design, configure, and troubleshoot computer networks at a CCNA-level of complexity. Packet Tracer supports student and instructor creation of simulations, visualizations, and animations of networking phenomena.
Like any simulation, Packet Tracer relies on a simplified model of networking devices and protocols. However, real computer networks remain the benchmark for understanding network behavior. Packet Tracer was created to help address the “digital divide” in networking education, where many students and teachers lack access to equipment, bandwidth, and interactive modes of learning networking.
Note: Let me assume you have some knowledge on routing.
LET US CREATE TOPOLOGY AND CONFIGURE DEVICES AS SHOWN IN DIAGRAM
(Click on image to enlarge)
PROCEDURE TO CREATE TOPOLOGY
- Start Packet Tracer
- Click on Routers in left bottom and drag 3 router model called 2621M onto the workspace
- Above model have 2 fast Ethernet ports.
- We have to add WIC-2T module to the router
- Switch off the router and drag the module in given 2 places in router back panel.
- WIC-2t Module:
The 2-port asynchronous/synchronous serial network module provides flexible multi-protocol support, with each port individually configurable in synchronous or asynchronous mode, offering mixed-media dial support in a single chassis. Applications for Asynchronous/Synchronous support include: Low speed WAN aggregation (up to 128 Kbps), dial-up modem support, Async or Sync connections to management ports of other equipment, and transport of legacy protocols such as Bi-sync and SDLC.
- Connect all routers using connection medium. Select automatic medium so that serial ports can be used.
- Assume center router be ISP side router and remaining 2 as Mumbai side router and the other as Delhi side router.
- Drag the switch of type 2960-24TT as shown.
- Drag the generic hosts and connect all of them.
- Now the topology is created like shown.
- Red dots indicate down-state and green dots indicate up-state.
Part 1: Designing the Network
Part 2: Configuring the Routers
What is a port?
In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint, providing a multiplexing service. It is used by Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).
A port number is a 16-bit unsigned integer, thus ranging from 0 to 65535.
A specific port is identified by its number, commonly known as the port number, the IP address with which it is associated, and the protocol used for communication.
Why do we need ports?
To support multitasking. Ports enable multiple programs to share a single physical network connection simultaneously, as opposed to having only one program using the connection for a long period of time.
In multitasking, multiple programs need to contact other programs on other computers over the network all at the same time, using ports and sockets.
Where do we specify port number so that packet knows which port to enter?
Transport Layer protocols, such as TCP, UDP specify a source and destination port number in their packet headers.
What is Binding?
A process associates its network input or output channels each with a particular port number, a process known as binding, to send and receive data. The operating system’s networking software has the task of transmitting outgoing data from all application ports onto the network, and forwarding arriving network packets to a process by matching the packets IP address and port numbers.
What is Listening?
Applications implementing common services often use specifically reserved, well-known port numbers for receiving service requests from client hosts. This process is known as listening and involves the receipt of a request on the well-known port and reestablishing one-to-one server-client communications on another private port, so that other clients may also contact the well-known service port.
The well-known ports are defined by convention overseen by the Internet Assigned Numbers Authority (IANA), cf. list of TCP and UDP port numbers.
What are Sockets?
Processes create associations with transport protocol ports by means of sockets. A socket is the software structure used as the transport end-point. It is created by the operating system for the process and bound to a socket address which consists of a combination of a port number and an IP address.
What is Port scanning?
Because different services commonly listen on different port numbers, the practice of attempting to connect to a range of ports in sequence on a single computer is commonly known as port scanning.
This is usually associated either with malicious cracking attempts or with network administrators looking for possible vulnerabilities to help prevent such attacks. Port connection attempts are frequently monitored and logged by computers. The technique of port knocking uses a series of port connections (knocks) from a client computer to enable a server connection.
An example for the use of ports is the Internet serving Web content through port 80, using available web servers like IIS or Apache.
Port numbers can occasionally be seen in the Uniform Resource Locator (URL) of a website or other services.
By default, HTTP uses port 80 and HTTPS uses port 443,
but a URL like http://www.localhost:8080/ specifies that the web site is served by the HTTP server on port 8080.
The port numbers are divided into three ranges: the well-known ports, the registered ports, and the dynamic or private ports. The well-known ports are those from 0 through 1023. Examples include:
53: Domain Name System
80: World Wide Web HTTP
443: HTTP over Transport Layer Security/Secure Sockets Layer
What is Architecture?
Architecture is the structure of software systems which is divided into different perspectives, allowing us to manage the complexity of software systems in a better and easier way.
A framework is a reusable software system with general functionality already implemented. It can be specialized into a ready-to-use application.
- Examples Zend Framework for PHP
- NET Framework for ASP etc
Benefits: The simple reuse of architecture and functionality
Drawbacks: A high degree of training effort, a lack of standards for the integration of different frameworks, and the resulting dependence on manufacturers.
Components of a Generic Web Application Architecture
Web browser sends a request to Web server and the response to this request is sent back.
Client = User agent. It is controlled by a user to operate the Web application. The client’s functionality can be expanded by installing plug-ins, add-ons and applets.
Firewall: A software or hardware regulating the communication between insecure networks (e.g., the Internet) and secure networks (e.g., corporate LANs). This communication is filtered by access rules.
Proxy: A proxy is typically used to temporarily store Web pages in a cache. However, proxies can also assume other functionalities, e.g., adapting the contents for users (customization), or user tracking.
Web server: A Web server is a software that supports various Web protocols like HTTP, and HTTPS, etc., to process client requests.
- Open source Apache Web Server
- IIS Web Server
- Tomcat Server
Database server: This server normally supplies an organization’s production data in structured form.
- Open source MySQL
- MS SQL Server
- Oracle database server
Media server: This component is primarily used for content streaming of non-structured bulk data like audio and video.
Content management server: Similar to a database server, a content management server holds contents to serve an application. These contents are normally available in the form of semi-structured data, e.g., XML documents.
Application server: An application server holds the functionality required by several applications, e.g., workflow or customization.
Legacy application: A legacy application is an older system that should be integrated as an internal or external component.
2-Layer Architectures = Client / Server Architechture
It uses a Web server to provide services to a client.
A client request can point directly to static HTML pages, without requiring any processing logic on the server layer, or it can access a database via the application logic on the Web server (e.g., in the form of CGI scripts).
Dynamic HTML pages include script instructions directly in the HTML code, e.g., when SSI (Server-Side Include) is used, and they are interpreted either by databases with HTML functionality or by a Web server. The application logic, or dynamic HTML pages, can use services (e.g., user identification or data encryption) when the HTML response is generated.
This architecture is suitable particularly for simple Web applications. In contrast, a multilayer architectural approach is required for more demanding applications which are accessed by a large number of concurrent clients or which provide complex business processes requiring the access to legacy systems, amongst others.
I have borrowed web engineering books from college library, and heres review for them
Authors: Gerti Kappel, Birgit Pryyll, Siegfried Reich, Werner Retschitzegger
Mumbai University has outlined there syllabus, using index page of this book.
This book defines concepts, methods, techniques and tools to demonstrate how to design, implement and test web applications. It also demonstrates the distinctions between software engineering and web engineering. It features a constant focus on interactivity, with a far greater emphasis on multimedia than its software counterpart.
Authors: Roger Pressman and David Lowe
Extremely technical, you could say its perfectly professional approach towards building web application. The book index page doesnt match with the university provided content. There is possibility of challenging questions from this book