How DHCP Server Work Posted Date: 06 Nov 2009     Resource Type: Articles/Knowledge Sharing     Category: Computer & Technology Author: Sukhsagar Prajapati Member Level: Gold     Rating: Points: 15 (Rs 15)

DHCP is a good known word in the networking. DHCP means Dynamic Host Configuration Protocol. Most of you already know that computers identify each other on network with their IP address, which is nothing, but a 32-bit number assigned to computers by network administrator manually or automatically through DHCP Server. In a computer network of around 10-20 computers it is not difficult to assign IP address to computers manually and keep track of them, but in a big network of more then 50-100 computers it will become a tough job for network administrator to manage the IP addresses manually. So the solution for that is to install and configure a DHCP server on your network. Network administrator needs to setup the DHCP server only and rest of the thing will be taken care by DHCP server. It will assign the IP address to the clients as per the request generated by them. So what is the process of installing and configuring a DHCP server? It is not very difficult to install and configure a DHCP server. DHCP is a service in Windows 2000/2003 server. Once you install any of these operating systems you can easily install DHCP server through add/remove windows components. Once you finished installing the DHCP server you need to create scope of IP address, which can be assigned to clients on the network. A scope is a range of IP address from which DHCP server assigns the IP address to the clients. One thing, which is very important from client side, is that all clients need to be configured to get IP address from DHCP server. You can do this by going into TCP/IP properties and selecting obtain an IP address automatically. Now I would explain how the clients get IP address from DHCP server. As soon as the clients switched on it broadcasts a message on network to check if there is a DHCP server present on network or not. This process is called DHCP discover in which client sends a discover message on network. Now if there is a DHCP server available on network it will get the clients message and offer an IP address to the client. Once the clients gets offer from DHCP server it will again request to the DHCP server to assign the IP address to the client. Now when the DHCP server receives the client’s request and assigns an IP address to client. This is called acknowledgement. By default IP address is assigned to a client for 8 days which is called a lease duration. In lease time DHCP server can allocate an IP address to client and reclaim it once the lease has expired. There can be more than one DHCP server in your network for load balancing or fail over. But this can be a little bit confusing. You must be thinking that if there are 2 DHCP servers on the network then who will assign the IP address first. This is very simple as when the client send the DHCP discover message whichever server will get it first will assign the IP address to the client. There can be cases when you want to give a fix IP to some resources on the network, for example a printer. Once an IP address assigned to a printer that needs to be same as all the clients on the network are connected to it. So what can be done is that you can reserve that IP address for the printer only by binding the MAC address of printers network card to the IP address in DHCP server. This way whenever a discover message will come from that printer only the binded IP address will be assigned to it. This can be done for Laptop or some dedicated Computers also. There is one more feature I would like to discuss here is that IP address exclusion. What does than means? It means that if you want that DHCP server does not assign certain IP addresses to any of the clients then you can exclude those IP address by creating an entry in IP address exclusion. Once you have excluded an IP address in DHCP server that IP address will not be assigned to any resource. Excluded IP addresses are often used to assign to Switches, Routers and other network devices since IP address of these devices is fixed cannot be changed very often. Sukhsagar Prajapati

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