EC301-COMPUTER NETWORK FUNDAMENTALS

UNDERSTAND NETWORK SERVICE

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Network Service

Definion & function :• Basic network computing environment. It is generally

provided in one or more servers to provide shared resources to client computers.

• To ensure security and user friendly operation. It helps LAN (Local Area Network) run smoothly and efficiently

Figure 1 :Network Services

Common Network Services

• Domain Name System (DNS)• Dynamic Host Configuration Protocol (DHCP)• Authentication Server• Directory Services• E-mail• Printing• File Sharing

Domain Name System (DNS)

• A system that stores information about host names and domain names on a network such as the Internet.

• Most importantly, it provides an IP address for each host name and a list of mail exchange servers that receives mail for each domain.

• DNS plays an important role because the hardware requires Internet IP addresses to perform routing and men use the host name and domain name for example the Uniform Resource Locator (URL) and e-mail address.

How DNS works

The domain name consists of two or more parts (labels) separated by dots (●). Labels on the right is the top-level domain (for example top-level domain to www.wikipedia.org is org). Each label to the left to determine subdivision or subdomain (for example, wikipedia.org is a subdomain of the org and subdomains to wikipedia.org is www.wikipedia.org).

www.wikipedia.org

subdomain (wikipedia.org) top-level domain (org)

• DNS consists of a hierarchical set of DNS servers. Each domain has one or more authentic DNS server (DNS authoritative serves) that publish information about that domain. Authentic hierarchy of DNS servers have a match with the domain hierarchy.

• An commonly used analogy to explain DNS is that it works as a phone book for the Internet by translating friendly computer hostnames into IP addresses man. For example, the domain name www.example.com translates to the addresses 192.0.43.10 (IPv4) and 2620:0:2 d0: 200 :: 10 (IPv6).

• DNS will distribute the responsibility for providing domain names and mapping of names to IP addresses by setting the authoritative name servers for each domain name. Therefore the authoritative server responsible for a particular domain, which may set other authoritative name servers for their sub-domains.

• DNS also specifies the technical functionality of this database service. It is defined as DNS protocol. Detailed specification of data structures and communication exchanges used in DNS is part of the Internet Protocol Suite.

Figure 2 : DNS Network Services

•http://www.youtube.com/watch?v=JtOlK4Kbx2w

Ping Command

• Ping is a computer network administration utility used to test whether a particular host is reachable across an Internet Protocol (IP) network and to measure the round-trip time for packets sent from the local host to a destination computer, including the local host's own interfaces.

• Ping operates by sending Internet Control Message Protocol (ICMP) echo request packets to the target host and waits for an ICMP response.

Browser

• network browser is a tool used to browse a computer network. • An example of this is My Network Places (or Network

Neighborhood in earlier versions of Microsoft Windows). • An actual program called Network Browser is offered in Mac OS 9.

Nslookup

• nslookup is a computer program used in Windows and Unix to query Domain Name System (DNS) servers to find DNS details, including IP addressed of a particular computer, MX records for a domain and the NS server of a domain.

• The name nslookup means "name server lookup".• The most common version of the program is

included as part of the BIND package.

IMPLIMENT DNS IN A LAN

• Corporate LANs use network services such as DNS to give names to IP and MAC addresses and DHCP to ensure that everyone on the network has a valid IP address.

• For example, names like “nm.lan” is better than numbers like “210.121.67.18”,

2.5.4 RELATIONSHIP BETWEEN WEB CLIENTS AND SERVERS

Web client??is actually your browser. It is the browser on you PC/Mac that makes the requests to the remote server. A PC/Mac that uses a web (Client) browser is referred to as a Client Machine.

Web Server??is basically a PC that is designed to accept requests from remote computers and send on the information requested.

• A web server is a computer program that delivers (serves) content, such as web pages, using the Hypertext Transfer Protocol (HTTP), over the World Wide Web.

• Refer to the computer or virtual machine running the program.

• The primary function of a web server is to deliver web pages to clients.

• A client, commonly a web browser or web crawler, initiates communication by making a request for a specific resource using HTTP and the server responds with the content of that resource, or an error message if unable to do so

2.5.5 RELATIONSHIP BETWEEN FTP CLIENTS AND SERVERS

What is FTP Client?personal computer or a mobile device that is running application software that is able to communicate with and retrieve files from a FTP server.

What is FTP Server?high powered device that holds the files and other information that is required to satisfy the requests coming from clients over the internet/intranet. FTP server continuously runs and listens for incoming FTP requests.

• File Transfer Protocol (FTP) is a standard network protocol used to copy a file from one host to another over a TCP/IP-based network, such as the Internet.

• FTP is used with user-based password authentication or with anonymous user access.

• Example :A client makes a connection to the server on TCP port 21. This connection, called the control connection, remains open for the duration of the session, with a second connection, called the data connection, on port 20 opened as required to transfer file data.

• The control connection is used to send administrative data (i.e., commands, identification, passwords).

• The server responds on the control connection with three digit status codes in ASCII with an optional text message, for example "200" (or "200 OK.") means that the last command was successful.

• The numbers represent the code number and the optional text represent

E-mail protocols in clients and servers have 3 types :

• SMTP• POP3• IMAP4

Types E-mail protocols

SMTP• Simple mail transfer protocol (SMTP) is an

internet standard for electronic mail (e-mail) transmission across internet protocol (IP) networks.

• SMTP was first defined in RFC821 and last updated by RFC5321 which includes the extended SMTP (ESMTP) additions .

• SMTP is specified for outgoing mail transport and uses transmission control protocol (TCP) port 25.

• Electronic mail servers and other mail transfer agents used SMTP to send and receive mail message.

• User–level client mail use SMTP for sending messages to mail server for relaying.

• For receiving message, client applications usually use :

i. Post office protocol (POP)ii. Internet message access protocol (IMAP)iii. Proprietary system ( such as Microsoft

Exchange or Locus Notes/Domino)

POP3• Post office protocol (POP) is an application –

layer internet standard protocol used by local e-mail clients to retrieve e-mail from a remote server over a TCP/IP connection.

• POP and IMAP are two most prevalent Internet standard protocols for e-mail retrieval.

• POP3 is a being current standard• POP3 is used for most mail clients such as : i. Gmailii. Yahoo

IMAP4

• The internet message access protocols (IMAP) is one of the two most prevalent internet standard protocols for email retrieval, the other being the post office protocols (POP).

• IMAP4 permits manipulation of remote message folders called "mailboxes", in a way that is functionally equivalent to local mailboxes.

• IMAP4 also provides the capability for an offline client to resynchronize with the server (see also [IMAP-DISC]).

• IMAP4 includes operations for creating, deleting, and renaming mailboxes, checking for new messages, permanently removing messages, setting and clearing flags.

OrganizationalNetworks are typically managed by the organizations that own them. Private enterprise networks may use a combination of intranets and extranets. They may also provide network access to the Internet, which has no single owner and permits virtually unlimited global connectivity.

Intranets and extranet

• Intranets and extranets are parts or extensions of a computer network, usually a LAN.

• An intranet is a set of networks that are under the control of a single administrative entity. The intranet uses the IP protocol and IP-based tools such as web browsers and file transfer applications. The administrative entity limits use of the intranet to its authorized users. Most commonly, an intranet is the internal network of an organization. A large intranet will typically have at least one web server to provide users with organizational information.

An extranet is a network that is also under the administrative control of a single organization, but supports a limited connection to a specific external network. For example, an organization may provide access to some aspects of its intranet to share data with its business partners or customers. These other entities are not necessarily trusted from a security standpoint. Network connection to an extranet is often, but not always, implemented via WAN technology.

InternetworkAn internetwork is the connection of multiple computer networks via a common routing technology using routers.

Internet

• The Internet is the largest example of an internetwork. It is a global system of interconnected governmental, academic, corporate, public, and private computer networks. It is based on the networking technologies of the Internet Protocol Suite. It is the successor of the Advanced Research Projects Agency Network (ARPANET) developed by DARPA of the United States Department of Defense. The Internet is also the communications backbone underlying the World Wide Web (WWW).

• Participants in the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP addresses) administered by the Internet Assigned Numbers Authority and address registries. Service providers and large enterprises exchange information about the reachability of their address spaces through the Border Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths.

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