8/3/2019 Internet Te

http://slidepdf.com/reader/full/internet-te 1/12

Routers

A device that forwards data packets along networks. A router is connected to at least twonetworks, commonly two LANs or WANs or a LAN and its ISP?? s network. Routers are locatedat gateways, the places where two or more networks connect.

routers use headers and forwarding tables to determine the best path for forwarding the packets,and they use protocols such as ICMP to communicate with each other and configure the bestroute between any two hosts.

Brouter 

bridge router and pronounced BROW-ter, a device that functions as both a router 

and a bridge. A brouter understands how to route specific types of packets, such as

 TCP/IP packets. Any other packets it receives are simply forwarded to other

network(s) connected to the device (this is the bridge function).

Repeaters

A network device used to regenerate or replicate a signal. Repeaters are used in transmissionsystems to regenerate analog or digital signals distorted by transmission loss. Analog repeatersfrequently can only amplify the signal while digital repeaters can reconstruct a signal to near itsoriginal quality.

In a data network, a repeater can relay messages between subnetworks that use different protocols or cable types. Hubs can operate as repeaters by relaying messages to all connectedcomputers. A repeater cannot do the intelligent routing performed by bridges and routers. 

Hub

A common connection point for devices in a network . Hubs are commonly used to connect

segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it iscopied to the other ports so that all segments of the LAN can see all packets.

Passive hub

A passive hub serves simply as a conduit for the data, enabling it to go from one device (or segment) to another. So-called intelligent hubs include additional features that enables anadministrator to monitor the traffic passing through the hub and to configure each port in thehub. Intelligent hubs are also called manageable hubs. 

Swich

A third type of hub, called a switching hub, actually reads the destination address of each packetand then forwards the packet to the correct port.

The Differences Between Hubs, Switches, and Routers on theNetwork the hub and the switch since these two devices have similar roles on the network. Each serves asa central connection for all of your network equipment and handles a data type known as frames.Frames carry your data. When a frame is received, it is amplified and then transmitted on to the port of the destination PC.

8/3/2019 Internet Te

http://slidepdf.com/reader/full/internet-te 2/12

The big difference between these two devices is in the method in which frames are being

delivered.

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.

A switch, however, keeps a record of the MAC addresses of all the devices connected to it. With

this information, a switch can identify which system is sitting on which port. So when a frame is

received, it knows exactly which port to send it to, without significantly increasing network 

response times. And, unlike a hub, a 10/100Mbps switch will allocate a full 10/100Mbps to each

of its ports. So regardless of the number of PCs transmitting, users will always have access to the

maximum amount of bandwidth. It's for these reasons why a switch is considered to be a much

 better choice then a hub.

 

All routers have a WAN Port that connects to a DSL or cable modem for broadband Internet

service and the integrated switch allows users to easily create a LAN. This allows all the PCs on

the LAN to have access to the Internet and Windows file and printer sharing services.

Some routers have a single WAN port and a single LAN port and are designed to connect an

existing LAN hub or switch to a WAN. Ethernet switches and hubs can be connected to a router 

with multiple PC ports to expand a LAN. Depending on the capabilities (kinds of available ports)

of the router and the switches or hubs, the connection between the router and switches/hubs may

require either straight-thru or crossover (null-modem) cables. Some routers even have USB  ports, and more commonly, wireless access points built into them.

Routers are also the only one of these three devices that will allow you to share

a single IP address among multiple network clients.

A web browser

is a software application for retrieving, presenting, and traversing information resources on theWorld Wide Web. An information resource is identified by a Uniform Resource Identifier (URI)

and may be a web page, image, video, or other piece of content.

[2]

 Hyperlinks present inresources enable users easily to navigate their browsers to related resources.

A web browser can also be defined as an application software or program designed to enableusers to access, retrieve and view documents and other resources on the Internet.

Although browsers are primarily intended to access the World Wide Web, they can also be usedto access information provided by web servers in private networks or files in file systems. The

major web browsers are Firefox, Google Chrome, Internet Explorer , Opera, and Safari.[3]

8/3/2019 Internet Te

http://slidepdf.com/reader/full/internet-te 3/12

The primary purpose of a web browser is to bring information resources to the user. This process begins when the user inputs a Uniform Resource Locator (URL), for examplehttp://en.wikipedia.org/ , into the browser. The prefix of the URL, the Uniform ResourceIdentifier or URI, determines how the URL will be interpreted. The most commonly used kind of URI starts with http: and identifies a resource to be retrieved over the Hypertext Transfer Protocol (HTTP). Many browsers also support a variety of other prefixes, such as https: for HTTPS, ftp: for the File Transfer Protocol, and  file: for local files.

Prefixes that the web browser cannot directly handle are often handed off to another applicationentirely. For example, mailto: URIs are usually passed to the user's default e-mail application,and news: URIs are passed to the user's default newsgroup reader.

In the case of http, https, file, and others, once the resource has been retrieved the web browser will display it. HTML is passed to the browser's layout engine to be transformed from markup toan interactive document.

Aside from HTML, web browsers can generally display any kind of content that can be part of aweb page. Most browsers can display images, audio, video, and XML files, and often have plug-ins to support Flash applications and Java applets. Upon encountering a file of an unsupported

type or a file that is set up to be downloaded rather than displayed, the browser prompts the user to save the file to disk.

Information resources may contain hyperlinks to other information resources. Each link containsthe URI of a resource to go to. When a link is clicked, the browser navigates to the resourceindicated by the link's target URI, and the process of bringing content to the user begins again.

User interface

Most major web browsers have these user interface elements in common:[20]

•  Back and forward buttons to go back to the previous resource and forward respectively.

• A refresh or reload button to reload the current resource.

• A stop button to cancel loading the resource. In some browsers, the stop button is mergedwith the reload button.

• A home button to return to the user's home page.

• An address bar to input the Uniform Resource Identifier  (URI) of the desired resourceand display it.

• A search bar to input terms into a search engine. In some browsers, the search bar ismerged with the address bar.

• A status bar  to display progress in loading the resource and also the URI of links whenthe cursor hovers over them, and page zooming capability.

Major browsers also possess incremental find features to search within a web page.

[edit] Privacy and security

Most browsers support HTTP Secure and offer quick and easy ways to delete the web cache,cookies, and browsing history. For a comparison of the current security vulnerabilities of  browsers, see comparison of web browsers.

8/3/2019 Internet Te

http://slidepdf.com/reader/full/internet-te 4/12

[edit] Standards supportof non-standard dialects of HTML, leading to problems withinteroperability. Modern web browsers support a combination of standards-based and de facto HTML and XHTML, which should be rendered in the same way by all browsers.

[edit] Extensibility

A browser extension is a computer program that extends the functionality of a web browser.Every major web browser supports the development of   browser extensions.

Top of Form

 

Proxy server 

In the general sense, a proxy is a stand in; in network architecture, it's an entity that sits betweencorporate client machines and the Internet.

A forward proxy stands in the way of the Internet and receives data from client machines boundfor the Internet and forwards it on on their behalf.

A reverse proxy stands in the way of servers within the corporate network and receives datafrom Internet bound for them, and distributes it on.

The original reason for having a forward proxy server was to share an Internetconnection between multipleclient machines whilereducing Internet traffic and

speeding up browsing bycaching Internet contentlocally on the proxy server.

Whenever content was required from the Internet, the client would establish a connection withthe proxy server, which would provide the content from its cache, if it could (otherwise it wouldestablish its own connection with the content server), retrieve the content, and then forward it tothe requesting client.

A forward proxy stands in theway of the Internet and receivesdata from client machines boundfor the Internet and forwards iton on their behalf. A reverseproxy stands in the way of servers within the corporatenetwork and receives data

bound for them, and distributesit on.

8/3/2019 Internet Te

http://slidepdf.com/reader/full/internet-te 5/12

When you think about it, there is not much difference between a proxy server and a NAT router  — assuming the caching function is left to one side. Both enable multiple machines on one sideto share an Internet connection, and both do so by receiving packets from those machines andsending them on. A proxy sever initiates another TCP connection while a NAT router simplymodifies packet headers, but the end result is the same.

Microsoft's Proxy Server, for example, was replaced by ISA Server, which is a Web cache,security system, and firewall in one.

Microsoft's ISA Server, as mentioned, is a hybrid proxy and firewall. It can perform contentcaching as well as deep content inspection and other security services.

Domain Name System

The Domain Name System (DNS) is a hierarchical distributed naming system for computers,services, or any resource connected to the Internet or a private network .

The Domain Name System makes it possible to assign domain names to groups of Internetresources and users , independent of each entity's physical location.

Internet domain names are easier to remember than IP addresses such as 208.77.188.166

(IPv4) or 2001:db8:1f70::999:de8:7648:6e8 (IPv6).

The Domain Name System distributes the responsibility of assigning domain names and

mapping those names to IP addresses by designating authoritative name servers for each domain.Authoritative name servers are assigned to be responsible for their particular domains, and inturn can assign other authoritative name servers for their sub-domains. This mechanism hasmade the DNS distributed and fault tolerant and has helped avoid the need for a single centralregister to be continually consulted and updated.

In general, the Domain Name System also stores other types of information, such as the list of mail servers 

The Domain Name System also defines the DNS protocol, a detailed specification of the datastructures and communication exchanges used in DNS, as part of the Internet Protocol Suite.

The Internet maintains two principal namespaces, the domain name hierarchy[3] and the Internet

Protocol (IP) address spaces.[4]

 The Domain Name System maintains the domain name hierarchy and provides translationservices between it and the address spaces. Internet name servers and a communication protocolimplement the Domain Name System.[5] 

A DNS name server is a server that stores the DNS records for a domain name,

8/3/2019 Internet Te

http://slidepdf.com/reader/full/internet-te 6/12

on most modern operating systems by default and generally contains a mapping of the IP address127.0.0.1 to "localhost". Many operating systems use name resolution logic that allows theadministrator to configure selection priorities for available name resolution methods.

The rapid growth of the network made a centrally maintained, hand-crafted HOSTS.TXT fileunsustainable; it became necessary to implement a more scalable system capable of 

automatically disseminating the requisite information.

Domain name space

The domain name space consists of a tree of domain names. Each node or leaf in the tree haszero or more resource records, which hold information associated with the domain name.

The tree sub-divides into zones beginning at the root zone. A DNS zone may consist of only onedomain, or may consist of many domains and sub-domains, depending on the administrativeauthority delegated to the manager.

 The hierarchical Domain Name System, organized into zones, each served by a

name server

Name servers

The Domain Name System is maintained by a distributed database system, which uses the client-server  model. The nodes of this database are the name servers. Each domain has at least oneauthoritative DNS server that publishes information about that domain and the name servers of any domains subordinate to it. The top of the hierarchy is served by the root nameservers, theservers to query when looking up (resolving ) a TLD.

8/3/2019 Internet Te

http://slidepdf.com/reader/full/internet-te 7/12

Authoritative name server

An authoritative name server is a name server that gives answers that have been configured byan original source, for example, the domain administrator or by dynamic DNS methods, incontrast to answers that were obtained via a regular DNS query to another name server. Anauthoritative-only name server only returns answers to queries about domain names that have

 been specifically configured by the administrator.An authoritative name server can either be a master server or a slave server. A master server is aserver that stores the original (master ) copies of all zone records. A slave server uses anautomatic updating mechanism of the DNS protocol in communication with its master tomaintain an identical copy of the master records.

Every DNS zone must be assigned a set of authoritative name servers that are installed in NSrecords in the parent zone.

When domain names are registered with a domain name registrar , their installation at the domainregistry of a top level domain requires the assignment of a primary name server and at least one secondary name server. The requirement of multiple name servers aims to make the domain stillfunctional even if one name server becomes inaccessible or inoperable.[12] The designation of a primary name server is solely determined by the priority given to the domain name registrar. For this purpose, generally only the fully qualified domain name of the name server is required,unless the servers are contained in the registered domain, in which case the corresponding IPaddress is needed as well.

Primary name servers are often master name servers, while secondary name server may beimplemented as slave servers.

An authoritative server indicates its status of supplying definitive answers, deemed authoritative, by setting a software flag (a protocol structure bit), called the Authoritative Answer ( AA) bit in itsresponses.[5] This flag is usually reproduced prominently in the output of DNS administrationquery tools (such as dig) to indicate that the responding name server is an authority for the

domain name in question.[5]

[edit] Recursive and caching name server

In principle, authoritative name servers are sufficient for the operation of the Internet. However,with only authoritative name servers operating, every DNS query must start with recursivequeries at the root zone of the Domain Name System and each user system must implementresolver software capable of recursive operation.

To improve efficiency, reduce DNS traffic across the Internet, and increase performance in end-user applications, the Domain Name System supports DNS cache servers which store DNS queryresults for a period of time determined in the configuration (time-to-live) of the domain namerecord in question. Typically, such caching DNS servers, also called DNS caches, alsoimplement the recursive algorithm necessary to resolve a given name starting with the DNS rootthrough to the authoritative name servers of the queried domain. With this function implementedin the name server, user applications gain efficiency in design and operation.

[edit] Operation

[edit] Address resolution mechanism

8/3/2019 Internet Te

http://slidepdf.com/reader/full/internet-te 8/12

Domain name resolvers determine the appropriate domain name servers responsible for thedomain name in question by a sequence of queries starting with the right-most (top-level)domain label.

Web server 

it serves static content to a Web browser at a basic level. This means that the Web server receives a request for a Web page such as

http://www.Webcompare.com/index.html

and maps that Uniform Resource Locator (URL) to a local file on the host server.

In this case, the file

index.html

is somewhere on the host file system. The server then loads this file from disk andserves it out across the network to the user's Web browser. This entire exchange is

mediated by the browser and server talking to each other using Hypertext Transfer

Protocol (HTTP). This workflow is shown in the figure below.

8/3/2019 Internet Te

http://slidepdf.com/reader/full/internet-te 9/12

That's all there is to it.

But if it's that simple, then why such an in-depth tutorial?

Because this simple arrangement, which allows the serving of static content such as HyperTextMarkup Language (HTML) and image files to a Web browser was the initial concept behindwhat we now call the World Wide Web. The beauty of its simplicity is that it has led to much

more complex information exchanges being possible between browsers and Web servers.

Perhaps the most important expansion on this was the concept of dynamic content (i.e., Web pages created in response to a user's input, whether directly or indirectly). The oldest and mostused standard for doing this is Common Gateway Interface (CGI). This is a pretty meaninglessname, but it basically defines how a Web server should run programs locally and transmit their output through the Web server to the user's Web browser that is requesting the dynamic content.

For all intents and purposes the user's Web browser never really has to know that the content isdynamic because CGI is basically a Web server extension protocol. The figure below showswhat happens when a browser requests a page dynamically generated from a CGI program.

Web server can refer to either the hardware (the computer) or the software (the computer application) that helps to deliver content that can be accessed through the Internet.[1]

The most common use of web servers is to host web sites but there are other uses such as datastorage or running enterprise applications.

The primary function of a web server is to deliver web pages on the request to clients. Thismeans delivery of HTML documents and any additional content that may be included by a

document, such as images, style sheets and scripts.A client, commonly a web browser or  web crawler , initiates communication by making a requestfor a specific resource using HTTP and the server responds with the content of that resource or an error message if unable to do so. The resource is typically a real file on the server's secondarymemory, but this is not necessarily the case and depends on how the web server is implemented.

While the primary function is to serve content, a full implementation of HTTP also includesways of receiving content from clients. This feature is used for submitting web forms, includinguploading of files.

8/3/2019 Internet Te

http://slidepdf.com/reader/full/internet-te 10/12

Many generic web servers also support server-side scripting, e.g., Active Server Pages (ASP)and PHP. This means that the behaviour of the web server can be scripted in separate files, whilethe actual server software remains unchanged. Usually, this function is used to create HTMLdocuments "on-the-fly" as opposed to returning fixed documents. This is referred to as dynamic and static content respectively. The former is primarily used for retrieving and/or modifyinginformation from databases. The latter is, however, typically much faster and more easilycached.

Web servers are not always used for serving the world wide web. They can also be foundembedded in devices such as  printers, routers, webcams and serving only a local network . Theweb server may then be used as a part of a system for monitoring and/or administrating thedevice in question. This usually means that no additional software has to be installed on theclient computer, since only a web browser is required (which now is included with mostoperating systems).

[edit] History of web servers• Virtual hosting to serve many Web sites using one IP address

• Large file support to be able to serve files whose size is greater than 2 GBon 32 bit OS

• Bandwidth throttling to limit the speed of responses in order to notsaturate the network and to be able to serve more clients

• Server-side scripting to generate dynamic Web pages, still keeping webserver and website implementations separate from each other

[edit] Path translationWeb servers are able to map the path component of a Uniform Resource Locator (URL) into:

• A local file system resource (for static requests)

• An internal or external program name (for dynamic requests)For a static request the URL path specified by the client is relative to the web server's rootdirectory.

Consider the following URL as it would be requested by a client:

http://www.example.com/path/file.html

The client's user agent will translate it into a connection to www.example.com with the followingHTTP 1.1 request:

GET /path/file.html HTTP/1.1

Host: www.example.com

The web server on www.example.com will append the given path to the path of its root directory.

On an Apache server , this is commonly /home/www (On Unix machines, usually /var/www). Theresult is the local file system resource:

/home/www/path/file.html

The web server then reads the file, if it exists and sends a response to the client's Web browser.The response will describe the content of the file and contain the file itself or an error messagewill return saying that the file does not exist or is unavailable.

8/3/2019 Internet Te

http://slidepdf.com/reader/full/internet-te 11/12

The Internet protocol suite is the set of communications protocols used for the Internet andother similar networks. It is commonly known as TCP/IP from its most important protocols:Transmission Control Protocol (TCP) and Internet Protocol (IP), which were the first networking

 protocols defined in this standard. Modern IP networking represents a synthesis of severaldevelopments that began to evolve in the 1960s and 1970s, namely the precursors of the Internetand local area networks, which emerged during the 1980s, together with the advent of the WorldWide Web in the early 1990s.

The Internet protocol suite classifies its methods and protocols into four hierarchical abstractionlayers. From the lowest to the highest communication layer, these are the link layer , the internetlayer , the transport layer , and the application layer .[1][2] The layers define the operational scope or reach of the protocols in each layer, reflected loosely in the layer names. Each layer hasfunctionality that solves a set of problems in its scope.

The link layer contains communication technologies for the local network to which the host isconnected directly by hardware components. The internet layer facilitates the interconnection of local networks. As such, this layer establishes the Internet. Host-to-host communication tasks arehandled in the transport layer, which provides a general application-agnostic framework totransmit data between hosts using protocols like the Transmission Control Protocol and the User Datagram Protocol (UDP). Finally, the highest-level application layer contains all protocols thatare defined each specifically for the functioning of the vast array of data communicationsservices. This layer handles application-based interaction on a process-to-process level betweencommunicating Internet hosts.

The Internet protocol suite uses encapsulation to provide abstraction of protocols and services.Encapsulation is usually aligned with the division of the protocol suite into layers of generalfunctionality. In general, an application (the highest level of the model) uses a set of protocols tosend its data down the layers, being further encapsulated at each level.

The transport layer establishes host-to-host connectivity, meaning it handles the details of datatransmission that are independent of the structure of user data and the logistics of exchanginginformation for any particular specific purpose. The layer simply establishes a basic data channelthat an application uses in its task-specific data exchange. For this purpose the layer establishesthe concept of the port , a numbered logical construct allocated specifically for each of thecommunication channels an application needs. For many types of services, these  port numbers have been standardized so that client computers may address specific services of a server computer without the involvement of service announcements or directory services.

The transport layer operates on top of the internet layer. The internet layer is not only agnostic of application data structures as the transport layer, but it also does not distinguish between

operation of the various transport layer protocols. It only provides an unreliable datagramtransmission facility between hosts located on potentially different IP networks by forwardingthe transport layer datagrams to an appropriate next-hop router for further relaying to itsdestination. With this functionality, the internet layer makes possible internetworking, theinterworking of different IP networks, and it essentially establishes the Internet. The InternetProtocol is the principal component of the internet layer, and it defines two addressing systems toidentify network hosts computers, and to locate them on the network. The original addresssystem of the ARPANET and its successor, the Internet, is Internet Protocol version 4 (IPv4). Ituses a 32-bit IP address and is therefore capable of identifying approximately four billion hosts.

8/3/2019 Internet Te

http://slidepdf.com/reader/full/internet-te 12/12

This limitation was eliminated by the standardization of Internet Protocol version 6 (IPv6) in1998, and beginning production implementations in approximately 2006.

The lowest layer in the Internet protocol suite is the link layer. It comprises the tasks of specificnetworking requirements on the local link, the network segment that a hosts network interface isconnected to. This involves interacting with the hardware-specific functions of network 

interfaces and specific transmission technologies.