1. An Introduction to DHCP

DHCP stands for dynamic host configuration protocol. What it does is dynamically assign network settings from a server. In other words, instead of having to configure the parameters related to how your computer communicates with a network, it happens automatically.

Assigning an IP address dynamically is the most basic piece but there is a lot more to DHCP. This includes the netmask, host name, domain name, gateway and name servers. In addition, DHCP can supply other information such as a time server.

Many people are anti-DHCP, because they see it as a way that an ISP offers you an IP address that changes. This, of course, makes it difficult to advertise a server. On the other hand, DHCP can save you a lot of ongoing configuration work within your company or organization.

Besides the ISP-provided DHCP servers, they commonly exist in inexpensive router boxes. Netgear, Linksys and other vendors offer these systems with multiple LAN ports, an 802.11b wireless interface or both. The Netgear RP114 is an example of a wired LAN, while the Linksys WAP11 is an 802.11b type. Many other product choices are available. When you use one, the router box becomes the system that the ISP knows about, and all of your real computers hide behind this box.

2. Describes DHCP (Dynamic host configuration protocol):

2.1: DHCP (Dynamic host configuration protocol):

The most common networking protocol in use today, TCP/IP, requires that each network-capable computer have a unique 4-byte number (an IP address) assigned to it. As previously mentioned, DHCP is a protocol that allows individual computers on the network (LAN clients) to get their configuration from a DHCP Server. The most significant part of the information that a DHCP Server provides to its clients is the IP address, the DNS servers and the default gateway IP address.

The overall purpose of DHCP is to reduce the amount of time required to plan, configure and administer a network.

DHCP uses a client-server model to provide safe and reliable TCP/IP network configuration. At the same time, DHCP prevents possible address conflicts and human errors in the many TCP/IP LAN client configurations. Typical DHCP Server use is by companies of all sizes, Internet Service Providers, and whenever minimal configuration and maintenance of network parameters is required.

Other applications include networks with mobile PCs, e.g., laptops, notebooks and other mobile devices. These PCs are ideal DHCP clients as they need not be manually re-configured when they move.

2.2 BENEFITS OF DHCP:

Reliable IP address configuration. DHCP minimizes configuration errors caused by manual IP address configuration, such as typographical errors, or address conflicts caused by the assignment of an IP address to more than one computer at the same time.

Reduced network administration. DHCP includes the following features to reduce network administration:

Centralized and automated TCP/IP configuration.

The ability to define TCP/IP configurations from a central location.

The ability to assign a full range of additional TCP/IP configuration values by means of DHCP options.

The forwarding of initial DHCP messages by using a DHCP relay agent, thus eliminating the need to have a DHCP server on every subnet.

The advantage of using DHCP is that changes to the network, for example a change in the address of the DNS server, need only be changed at the DHCP server, and all network hosts will be reconfigured the next time their DHCP clients poll the DHCP server. As an added advantage, it is also easier to integrate new computers into the network, as there is no need to check for the availability of an IP address. Conflicts in IP address allocation are also reduced.

Control Major Network Resource Changes

2.3 HOW DOES IT WORKS:

• DHCPDISCOVER

The client broadcasts message in search of available DHCP servers.

• DHCPOFFER

The server response to the client DHCPDISCOVER with offer of configuration parameters.

• DHCPREQUEST

The client broadcasts to the server, requesting offered parameters from one server specifically.

Confirms correctness of previously allocated address after system reboot.

Extends the lease on a particular network address.

• DHCPRELEASE

The client-to-server communication, relinquishing network address and canceling remaining lease.

DHCPACK

The server-to-client communication with configuration parameters, including committed network address.

DHCPNAK

Server to client indicating client's notion of network address is incorrect (client has moved to new subnet) or client's lease as expired

DHCPDECLINE

The client-to-server communication, indicating that the network address is already in use.

DHCPINFORM

The client-to-server communication, asking for only local configuration parameters that the client already has externally configured as an address.

Fig: working process of DHCP

3.Installization and configuration:

3.1 list of required hardware and software:

Hardware :..

1. Computers

2. Networking cables with RJ-45 connector

3. Cables stripper

4.PEN DRIVE

SOFTWARE:

1. ISC-DHCP-SERVER

3.2 Install and configure in Ubuntu:

Setp 1:

At a terminal prompt, enter the following command to install dhcpd:

sudo apt-get install isc-dhcp-server

You will probably need to change the default configuration by editing /etc/dhcp3/dhcpd.conf to suit your needs and particular configuration.

Step 2:

In this image,Server is install and also show the ISC-DHCP-SEVER start/running

Step3:

Now we configure the dhcp server . we are write the command sudo nano /etc/dhcp/dhcpd.conf.

Step 4

Now open the /etc/dhcp/dhcpd.conf file.

Now we edit some IP address from configuration

Step5

Now we see the a slightly different configuration for an internet subnet.we are see that some default value. We are changing the value for new configuration to setup DHCP server

Step6:

Hare we configure IP address by editing network conncetion

Step7

Hare we editing wired connections

Step8

Now we click the IPV4 settings options and changes the method automatic(DHCP) to MANUAL

Step10

Now we edit network connections Ethernet(wired conection) .we are edit method automatic to manual and setup address 192.168.1.1 net mask 255.255.255.0,gateway 192.168.1.1 then click reguried IPV4 adddressing for the connection to compeletes and click save buttom to save manual configaration

Step11

This will result in the DHCP server giving a client an IP address from the range 192.168.1.26 to 192.168.1.40. It will lease an IP address for 600 seconds if the client doesn't ask for a specific time frame. Otherwise the maximum (allowed) lease will be 7200 seconds. The server will also "advise" the client that it should use 255.255.255.0 as its subnet mask, 192.168.1.255 as its broadcast address, 192.168.1.1 as the router/gateway

Step12

When we change the value then have to save this new configuration by pressing CTRL+X and press Y to save this

Step13:

After reconfiguration we have to restart our server by typing command (SUDO SERVICE ISC-DHCP-SERVER RESTART )

4.TEST

4.1 Test with different cases

1. Clients Hardware address

2. The clients in IP address range

3. Justify with ping command

4.2 Test result with screenshots

Test no:1

For verify the clients IP we command to ping clients IP

For example: ping 192.168.1.1 -c 6 (its result will six time access)

Test no:2

Now we show the client network connection information .We know that DHCP server range is 192.168.1.26 to 192.168.1.40 . here we can see the client network IP=192.168.1.26.so we can justify this way

Test no 3.

Hare we can see clients hardware address.it also justify the DHCP server to clients network connection

5 Conclusion:

Assigning client addresses automatically is by far the easiest option of the two:

Set-up automatically by DHCP server Set-up manually

To set-up clients automatically all you need to do is  set your TCP/IP control panels to receive automatically

If you intend to set up your client computers manually, make sure that the assigned IP address is in the same range of your default router address and that it is unique to your private network

Some machines on your network need to be at fixed addresses, for example servers and routers

You need to be able to assign a machine to run the DHCP server continually as it must be available at all times when clients need IP access

References:

1. https://help.ubuntu.com/community/isc-dhcp-server 2. http://www.linuxjournal.com/article/8820 3. http://www.wikihow.com/Set-up-a-DHCP-Server-on-Ubuntu (installing and

configurimg)4. https://www.youtube.com/watch?v=9Vc6-0smd64 5. https://www.youtube.com/watch?v=NP23j7bcCNE 6. https://www.youtube.com/watch?v=Aq-StF7ovKA 7. https://www.youtube.com/watch?v=hFe81mkO_uY 8. http://xristina.uom.gr/linux/files/serverguide_ubuntu.pdf 9. https://help.ubuntu.com/lts/serverguide/serverguide.pdf 10. https://www.isc.org/wp-content/uploads/2014/08/DHCP-4.3.1-Distribution-

Documentation-Aug-4-14.pdf