Describe the steps taken by the client and DHCP server in order to obtain an IP address?

Answer 1

Firstly, a DHCP server is needed which distributes the IP addresses. This machine will serve as a base for all DHCP requests and must also have a fixed IP address. Therefore, on a network there can only be one machine with a fixed IP address, the DHCP server.

The basic communication system is BOOTP (with UDP frame). When a machine is turned on, it has no information on its network configuration, and there is nothing special that the user needs to do to find an IP address. In order to do this, the technique used is the broadcast: to find and talk with a DHCP server, the machine will simply send a special broadcast packet (broadcast on 255.255.255.255 with other information such as the type of request, the connection ports, etc.) over the local network. When the DHCP receives the broadcast packet, it will send back another broadcast packet (do not forget that the client does not obviously have the IP address and that therefore cannot be connected to directly) containing all the information required for the client.

It could be believed that one single packet is enough for the protocol to work. In fact, there are several types of DHCP packets likely to be issued either by the client for the server(s), or by the servers to a client:

DHCPDISCOVER (to locate available DHCP servers)

DHCPOFFER (server response to a DHCPDISCOVER packet, which contains the initial parameters)

DHCPREQUEST (varied request from the client for example to extend its lease)

DHCPACK (server response which contains the parameters and IP address of the client)

DHCPNAK (server response to indicate to the client that its lease has expired or if the client announces a bad network configuration)

DHCPDECLINE (the client announces to the server that the address is already in use)

DHCPRELEASE (the client releases its IP address)

DHCPINFORM (the client requests local parameters, it already has its IP address)

The first packet issued by the client is a DHCPDISCOVER type packet. The server responds with a DHCPOFFER packet, particularly in order to submit an IP address to the client. The client establishes its configuration and then makes a DHCPREQUEST to validate its IP address (a broadcast request since DHCPOFFER does not contain the IP address). The server simply responds with a DHCPACK with the IP address for confirmation of the allocation. Normally, this is enough for the client to obtain an effective network configuration, but it can be longer or shorter according to whether the client accepts the IP address or not.

Hope this will help you to understand DHCP.

Regards,
Jaydeep.Gatlewar@gmail.com

Answer 2

DORA

This process of assigning the IP addresses by the DHCP server also known as DORA (Discover Offer Request and Acknowledgement).

1. Client makes a UDP Broadcast to the server about the DHCP discovery.
2. DHCP offers to the client.
3. In response to the offer Client requests the server.
4. Server responds all the Ip Add/mask/gty/dns/wins info along with the acknowledgement packet.

• At least one DHCP server must exist on a network. Once the DHCP server software is installed, you create a DHCP scope, which is a pool of IP addresses that the server manages. When clients log on, they request an IP address from the server, and the server provides an IP address from its pool of available addresses.
• DHCP was originally defined in RFC 1531 (Dynamic Host Configuration Protocol, October 1993) but the most recent update is RFC 2131 (Dynamic Host Configuration Protocol, March 1997). The IETF Dynamic Host Configuration (dhc) Working Group is chartered to produce a protocol for automated allocation, configuration, and management of IP addresses and TCP/IP protocol stack parameters.

Answer 3

When a host computer connects to a network, it attempts to contact any DHCP servers available through a broadcast asking them for an available IP address. The DHCP servers then scan their pool of IP addresses and send one to the host along with info such as DNS server info, subnet mask, and default gateway. The host then sends a message back to the DHCP server to notify that it has accepted the IP address provided. Now you are connected to the network!