In this video from ITFreeTraining I will look at the basics of how Dynamic Host Configuration
Protocol or DHCP works. Once we understand the basics, the rest of the course will look
at how to deploy and configure DHCP in your organization.
DHCP was first developed in the early 90’s. It is designed to dynamically distribute network
configuration. There were other methods designed before this, but they did not include all
the features of DHCP. DHCP is now the standard for distributing network configuration.
To understand how DHCP works, I will first look at the components that make up DHCP.
First, there is the DHCP server component. This contains all the configuration for DHCP
and responds back to client requests for network configuration.
The next component is the DHCP client. This is the device on the network that sends requests
to the DHCP server. The server will respond back and the client will use this configuration.
The last component is the DHCP protocol. This defines the messages that are sent over the
network between the DHCP server and the DHCP client. Since the DHCP protocol is an open
protocol, all devices on the network can use it. All Windows’ client and server operating
systems support the DHCP Client. Also, all Windows Servers support the DHCP server component.
On the Linux side, all distributions support the DHCP client. There are also many different
implementations of the DHCP server. So regardless if you are using Windows, Linux or another
operating system, your client and server will support DHCP.
The next part of DHCP that I will look at is DHCP allocation methods. DHCP allocates
IP Addresses to devices on the network from pools. In Windows, these pools are called
scopes. There are three different ways it can allocate IP Addresses.
The first is dynamic. If you consider that there are a number of devices on the network,
these devices can be anything; desktops, phones, laptops or mobile devices. Any devices that
support DHCP which nowadays includes devices like smart TVs. If you can connect the device
to a network, it is more than likely that it supports DHCP.
When using the dynamic method of allocating IP addresses, devices are assigned an IP Address
from a pool of addresses. Once assigned, the device can use that IP Address. After a period
of time, the device will need to renew the IP Address if it wants to continue to use
it. If the device does not renew the IP Address, the IP Address is free to be allocated to
another device.
The dynamic method of IP Address allocation is commonly used on DHCP servers. For example,
the default configuration of a home DSL device will generally use the dynamic method to allocate
IP addresses. Dynamic allocation allows devices to come and go from the network.
If you consider a free wireless hotspot, for example in a café, you want it to have the
ability to allow any device to connect to it. If the device is disconnected for a short
period of time, for example an hour or so, you want the device to be able to continue
to use the same IP Address. However, if the device is disconnected for an extended period
of time, like days, it may not be connecting back to that network. It makes sense that
when this occurs, the DHCP server should reclaim the IP Address. If this did not occur, a device
could connect to a network the one time, never connect to it ever again but be permanently
allocated an IP Address on that network.
The next method of allocation is automatic. The method differs from dynamic in that when
a device is allocated an IP Address, it is permanently allocated that IP Address. This
is useful in companies where there are a limited number of devices connecting to the network.
The advantage is that even if the device changes networks, when it returns to the previous
network, it will always get the same IP Address. Having the same IP Address allocated for each
device is useful for auditing. If you find the IP Address in a log file, you know the
IP Address belongs to that dev ice. However, using the dynamic allocation method, a single
IP Address could have been used by many devices. Using the automatic allocation method, allows
you to be sure that only that device was using that IP Address.
The last allocation method that I will look at is the manual allocation method, in which
each device on the network is allocated a permanent IP Address. This sounds the same
as automatic allocation. However, the administrator is required to assign an IP Address to each
device before it is put on the network. This is called a reservation and will ensure that
the device will always get that IP Address. This gives the administrator ultimate control
over which IP Addresses go to which devices, but does require more work on the part of
the administrator.
This concludes this video. In later videos, I will look at DHCP in more detail and then
look at how to implement DHCP in your organization. Until those videos, I would like to thank
you for watching.