Starting and Stopping the Server

Important

When the DHCP server is started for the first time, it fails unless the dhcpd.leases file exists. Use the command touch /var/lib/dhcpd/dhcpd.leases to create the file if it does not exist.

If the same server is also running BIND as a DNS server, this step is not necessary, as starting the named service automatically checks for a dhcpd.leases file.

To start the DHCP service, use the command /sbin/service dhcpd start. To stop the DHCP server, use the command /sbin/service dhcpd stop.

If more than one network interface is attached to the system, but the DHCP server should only be started on one of the interfaces, configure the DHCP server to start only on that device. In /etc/sysconfig/dhcpd, add the name of the interface to the list of DHCPDARGS:

This is useful for a firewall machine with two network cards. One network card can be configured as a DHCP client to retrieve an IP address to the Internet. The other network card can be used as a DHCP server for the internal network behind the firewall. Specifying only the network card connected to the internal network makes the system more secure because users can not connect to the daemon via the Internet.

Other command line options that can be specified in /etc/sysconfig/dhcpd include:

· -p <portnum> — Specifies the UDP port number on which dhcpd should listen.

· -f — Runs the daemon as a foreground process. This is mostly used for debugging.

· -d — Logs the DHCP server daemon to the standard error descriptor. This is mostly used for debugging. If this is not specified, the log is written to /var/log/messages.

· -cf <filename> — Specifies the location of the configuration file. The default location is /etc/dhcpd.conf.

· -lf <filename> — Specifies the location of the lease database file. If a lease database file already exists, it is very important that the same file be used every time the DHCP server is started. It is strongly recommended that this option only be used for debugging purposes on non-production machines. The default location is /var/lib/dhcpd/dhcpd.leases.

· -q — Do not print the entire copyright message when starting the daemon.

4.Telecommunication technologies.

Telecommunications involves the transmission over long distances of all forms of information between computers various types of communication lines. By definition, to ensure prompt and accessible exchange of information files is necessary, that users had access to the Internet and software for data processing. All modern telecommunication technologies based on the use of networks.

Network resources are divided into these types:

• Hardware (servers);

• Software (provides reception, transmission and processing of information);

• Information (storage of different arrays of information).

There are several services, or types of services that are provided to consumers on the Internet. For their correct use is necessary to have two computers, one of them is a workstation user, and the second - the server is the source of network resources. The work of all services based on the use of application protocols that specify a list of rules to which all companies to ensure the compatibility of hardware and software. Also the data transfer is based on a client-server program, which involves client requesting services from the server.

The Internet can provide the following services:

• Telecommunication (messaging, information of various types and sizes, teleconference, etc.);

• Information (search for information in any format that the user interests);

• Consulting (training and advice on any matters relating to the use of public resources);

• Technical services (installation and testing of hardware and software);

• Commercial (all commercial activities on the Internet);

• On-line communication between subscribers;

• Placement of advertisements on various websites, social networks and other sites;

• Cellular and mobile communications.

The introduction of telecommunication technologies in different spheres of life

Initially telecommunication technologies conceived for uninterrupted messaging at a great distance. The uniqueness of the network was that it could properly function even after damage to its parts. Internet invented for military purposes, but it was leaked to a wide range of users and has been used successfully in many spheres of activity. With the help of scientists, students and professionals of different professions quick access to information in any format could facilitate its work. Search essential data in minutes, and the software provides them with the correct treatment. The opportunity to keep track of all the processes of personnel and execution of orders in remote access for executives, which greatly increased the productivity of labor.

Questions:

1. Why do we need to connect computers?

2. What is a computer network?

3. Briefly describe the following network components.

4. a. Client b. Server c. Hub d. Router

5. What are the differences between a Hub and a Switch?

6. How do we use a MODEM?

7. Describe the following categories of networks briefly

8. a. PAN b. LAN c. WAN d. MAN

9. Explain the classifications of networks according to the topology.

10. What does it mean Internet and Intranet? Why is it important to use intranet than internet?

11. What is the most suitable connection method for the following;

a. Computers within a laboratory.

b. Connect two computer laboratories.

References

1. June J. Parsons and Dan Oja, New Perspectives on Computer Concepts 16th Edition - Comprehensive, Thomson Course Technology, a division of Thomson Learning, Inc Cambridge, MA, COPYRIGHT © 2014.

2. Lorenzo Cantoni (University of Lugano, Switzerland) James A. Danowski (University of Illinois at Chicago, IL, USA) Communication and Technology, 576 pages.

3. Craig Van Slyke Information Communication Technologies: Concepts, Methodologies, Tools, and Applications (6 Volumes). ISBN13: 9781599049496, 2008, Pages: 4288

4. Utelbaeva A.K.,Utelbaeva A.K. Study guide for lectures on discipline “Computer science”, Shimkent 2008, 84 pages.