Dynamic Host Control Protocol.....

POST 1:  Just a very small introduction about DHCP

The DHCP server manages a pool of IP addresses and information about client configuration parameters such as default gateway, domain name, the DNS servers, other servers such as time servers, and so forth. On receiving a valid request, the server assigns the computer an IP address, a lease (length of time the allocation is valid), and other IP configuration parameters, such as the subnet mask and the default gateway. The query is typically initiated immediately after booting, and must complete before the client can initiate IP-based communication with other hosts. Depending on implementation, the DHCP server may have three methods of allocating IP-addresses:

• dynamic allocation: A network administrator assigns a range of IP addresses to DHCP, and each client computer on the LAN has its IP software configured to request an IP address from the DHCP server during network initialization. The request-and-grant process uses a lease concept with a controllable time period, allowing the DHCP server to reclaim (and then reallocate) IP addresses that are not renewed (dynamic re-use of IP addresses).
• automatic allocation: The DHCP server permanently assigns a free IP address to a requesting client from the range defined by the administrator. This is like dynamic allocation, but the DHCP server keeps a table of past IP address assignments, so that it can preferentially assign to a client the same IP address that the client previously had.
• static allocation: The DHCP server allocates an IP address based on a table with MAC address/IP address pairs, which are manually filled in (perhaps by a network administrator). Only requesting clients with a MAC address listed in this table will be allocated an IP address.

Bootp uses manual mapping of mac address-ip address. DHCP is introduced to overcome the issues with bootp.

Please add your comments and share extra information you have. So that it will be helpful for the other viewers....

Download the below setup to your pc and check how dhcp server works !!!!!

 

Sample Lab Environment illustration

Download Click

In the above lab setup you can find,

Routers R5,4,3,2 are acting as PCs having two connections to each ethernet switch.Each PC will be having two ports expecting dhcp assigned address from dhcp_server_7200.
The dhcp_server_7200 is having two address pools with 10.0.0.0 network and 192.168.1.0 network
respectively.

Once the network is ON, each PC will be getting an ip address from each pool.
The 192.168.1.0 pool is having very less lease time of 10mins "0 0 10", so the server will always be busy reallocating the
address.

The setup is still open for many enhancements !!
1.DHCP Relay.
2.DHCP Accounting.

~Kalyan
kaprakashr@gmail.com'

Remember you should have GNS3 to use the setup, in the download link. 

Download Click

~Kalyan
kaprakashr@gmail.com'