File services Domains, DNS 1 DHCP Server Scripts Intranet and Extranets Web services HNC COMPUTING - Network Concepts
A domain is a logical grouping of networked computers that share a central directory or database. Domains have several advantages: Centralized administration since all user information is stored centrally. A single logon process that enables users to access network resources as well as specify permissions that control who can and cannot access these services. The ability to expand a network to extremely large sizes throughout the world. BTEC L3 Unit 09 Computer Networks 2
Domain Name System The domain name system (DNS) is chiefly used to translate hostnames into numeric IP addresses DNS is an example of a distributed database If that server can resolve the hostname, it does so If not, that server asks another domain name server BTEC L3 Unit 09 Computer Networks 3
The DNS protocol allows clients to make requests to DNS servers in the network for the translation of names to IP addresses. Hostnames and the DNS services that computer systems run are all linked together. The Internet name that the DNS resolves to the IP address is also called the Hostname. The first part of the hostname is called the Machine Name and the second part is called the Domain Name. BTEC L3 Unit 09 Computer Networks 4
Domain Name System The very last section of the domain is called its top-level domain (TLD) name BTEC L3 Unit 09 Computer Networks 5
Domain Name System Organizations based in countries other than the United States use a top-level domain that corresponds to their two-letter country codes Some of the top-level domain names based on country codes BTEC L3 Unit 09 Computer Networks 6
Dynamic Host Configuration Protocol (DHCP) enables computers on an IP network to receive network configurations from the DHCP server. These servers have no information about the individual computers until information is requested. DHCP also allows for recovery and the ability to automatically renew network IP addresses through a leasing mechanism. This mechanism allocates an IP address for a specific time period, releases it and then assigns a new IP address. BTEC L3 Unit 09 Computer Networks 7
Scripts are considered to be much simpler than the standard programs and applications found in a NOS. The operating system sequentially processes the lines of code in a script file whenever the file is run. Most scripts are designed to execute from the top of the file to the bottom without requiring any input from the user. Many different scripting languages exist, and each offers their own advantages to the user: Visual Basic script (VBScript) JavaScript Linux shell scripting Perl, PHP, TCL, REXX, and Python BTEC L3 Unit 09 Computer Networks 8
Most average NOS users will not create and execute their own scripts. The majority of scripting is performed by system administrators and experienced users. The following examples demonstrate common scenarios where scripts are an appropriate solution: Logging on to the NOS Printing messages to the screen Installing software Automating complicated commands BTEC L3 Unit 09 Computer Networks 9
What is a Firewall? Firewall A machine and its software that serve as a special gateway to a network, protecting it from inappropriate access Filters the network traffic that comes in, checking the validity of the messages as much as possible and perhaps denying some messages altogether Enforces an organization s access control policy BTEC L3 Unit 09 Computer Networks 10
BTEC L3 Unit 09 Computer Networks 11
Intranets use the same technology used by the Internet, including HTTP over TCP/IP, web servers, and web clients. The difference between an intranet and the Internet is that intranets do not allow public access to private servers. One approach to building intranets is to configure them so that only on-site users can access the intranet servers. This is typically accomplished by using an Internet firewall. BTEC L3 Unit 09 Computer Networks 12
Extranets are configured to allow employees and customers to access the private network over the Internet. To prevent unauthorized access to the private network, extranet designers must use a technology such as virtual private networking. VPNs rely on encryption software, usernames, and passwords to ensure that communication occurs privately, and only among authorized users. BTEC L3 Unit 09 Computer Networks 13
Extranets provide a means of including the outside world such as customers and suppliers. Extranets can partition off and separate company data contained in the company intranet from the web services offered to the world via the Internet. Advantages of an extranet for a company could be e-mail, customer support, e- commerce, and program sharing. BTEC L3 Unit 09 Computer Networks 14
The World Wide Web is now the most visible network service. In less than a decade, the World Wide Web has become a global network of information, commerce, education, and entertainment. BTEC L3 Unit 09 Computer Networks 15
The Web is based on a clientserver model. Clients attempt to establish TCP sessions with web servers. Once established, a client can request data from the server. The Hypertext Transfer Protocol (HTTP) typically governs client requests and server transfers. Web client software includes GUI web browsers, such as Netscape Navigator and Internet Explorer. BTEC L3 Unit 09 Computer Networks 16
We have covered: Email File Sharing and Peer to Peer Domains, DNS, DHCP & Scripts Intranet and Extranets Web services Now complete the Packet Tracer Exercises 33 to 37 BTEC L3 Unit 09 Computer Networks 17