Questions about DHCP

[shiraforkosh1]

Hi,
There is something about DHCP that i can't understand.
I was told that the PC asks for an ip address by sending a broadcast(and then the router continues the proccess. From to this point i understand it).
My problem is with the beginning - how can the pc send a messege without having an ip? even if it has mac address, he stills need an ip.
And also, what would be the ip source and the ip destination in this broadcast frame? i know that there is broadcast messege layer 2 and 3, but still I can't understand how would look in this case.
When a PC wants to discover another PC(or any other network device), it sends an arp request, but it can only send it when it already has its ip, so i can't undertand how this proccess (the dhcp proccess- not the arp!)starts and ends without having ip of anyone.
Also a broadcast address in layer 3 is the last ip of a network, so how can the pc know what is its network id before it recives the ip address?
I hope you understand all my questions and help me with them.

[Reza Sharifi]

Hi,

Have a look at this document.  It describes the interaction between DHCP clients and server with diagrams.

DHCP uses a client-server model where one or more servers (DHCP servers) allocate IP addresses and other optional configuration parameters to clients (hosts) upon client bootup. These configuration parameters are leased by the server to the client for some specified amount of time. When a host boots up, the TCP/IP stack in the host transmits a broadcast (DHCPDISCOVER) message in order to gain an IP address and subnet mask, among other configuration parameters. This initiates an exchange between the DHCP server and the host. During this exchange, the client passes through the several well defined states listed below:

http://www.cisco.com/c/en/us/support/docs/ip/dynamic-address-allocation-resolution/27470-100.html

HTH

[Venkatesh Perumal]

go through the below links for explanation on the same.

http://www.geekinterview.com/question_details/55539

https://learningnetwork.cisco.com/thread/66351

-regards,