What is Dynamic Host Configuration Protocol OR DHCP? Know more

DHCP
It stands for Dynamic Host Configuration Protocol. Every computer or device on a network has to have an IP address for communication purposes. An IP address is like having a unique identifier for a computer or a device on a network and there are two ways that a computer can be assigned an IP address. It could be done by using a static IP or Dynamic IP.

Now a static IP address is manually assigned by a user to a computer or device. This was the method used for assigning IP addresses at the beginning of the networking. So for each computer, you need to open a configuration page and manually type in an IP address. But in addition to IP address you also need to type in a Subnet Mask, Default Gateway and a DNS Server and anytime you wanted to add another computer to the network then you had to repeat this same process again. So you can see that this could be a lot of work if you are dealing with large networks where there are a large number of computers and you also have to make sure that all the IP addresses are unique and if you assign the same IP address twice then it will cause an IP conflict and would cause those computers do not have access to the networks. But there is another easy way of assigning IP addresses to a computer. This is called a Dynamic IP.

A Dynamic IP is where a computer gets an IP address from DHCP server.

A DHCP server automatically assigns a computer an IP address along with Subnet Mask, Default Gateway, and DNS server.
So for an Ex:- We have a network connection properties window open for the network interface card on a Windows computer as you can set it to “Obtain an IP address automatically”. So when you choose this option the computer will broadcast a request for IP address on a network and the DHCP Server will assign an IP address from its port and deliver it to the computer. Once at a turn, you can verify all the settings that the DHCP server has given to the computer. You can verify it by running a command on command prompt i.e. Ipconfig on a windows computer.

If the DHCP is enabled on the computer then you can see that the computer is getting it’s IP address from a DHCP server and then you can see the IP address, Subnet Mask, Default Gateway and DNS server all these settings were given by a DHCP server. So as you can see Dynamic IP address setting is the best choice as you are getting automatic IP address and it makes managing a network lot easier.

DHCP server assigns IP addresses to a computer on a network from its Scope. A Scope is a range of IP addresses that a DHCP server can hands out. For ex. a scope of IP addresses on a server starts with 10.0.0.1 to 10.0.0.100. So the computers on this network will get the IP addresses in this range i.e. the scope can give 100 IP addresses. These values can be customized by either increasing or decreasing the range it all depends upon the network administrator as it is customizable.

When a computer obtains an IP address from a DHCP server, it assigns the IP address as a lease. So computer doesn’t actually own the IP address, it’s actually a lease.
A lease is an amount of time an IP address is assigned to a computer.

For ex. A lease could be for one day. The reason for the lease is to help make sure that the DHCP server does not run out of IP addresses in its scope. Ex. A network administrator has created a scope with only 4 IP addresses. When the 4 computers are added to the network the DHCP server will assign IP addresses to these computers. Now at this time the IP addresses are not leased, they will be given to the computers. So consider if we remove a computer from the network then that IP address will remain with the computer and if again a computer is added that time DHCP server has already been run out of IP addresses so the new computer won’t be able to access the network. So this is why IP addresses are leased and not given.

Thus this tells DHCP server which IP addresses are still being used and which addresses are not being used. So in this example, the IP addresses are leased. During the lease after some time the computer will request the DHCP server to renew the lease of the IP address or in other words, it’s informing a DHCP server that it’s still present on the network and it’s IP address is still being used. So if a computer is removed from a network then that computer is not going to ask for a renewal so if a computer doesn’t ask for a lease renewal then that lease will expire and the IP address will going back to the IP address pool. So the IP address can be used for another computer and this is why IP addresses are leased.
If you want a computer on your network to have a specific IP address all the time then you can create a reservation on a DHCP server. This reservation ensures that a specific computer or device will be identified by its Mac address i.e. it ensures that a specific computer or device will always be given the same IP address when that computer or device requests an IP address from the DHCP server.

For ex. If I create a reservation on a DHCP server for my computer then the DHCP server will recognize my Mac address and will always give me this specific IP address. The reservations are not typically given to regular computers, they are typically given to the special devices or computers such as network printers, servers, routers etc. Because devices like this should run on a server that could be a Microsoft server or a Linux server. But its also a service which runs on many routers. It can be a business router, small office router or router at home office.