Implementing DHCP

- [Instructor] Hello everyone. Welcome to Windows Server Networking. In this chapter, we will discuss networking for on-premises environment. We will start our discussion with implementing DHCP. We will discuss how to deploy DHCP server and we will also dive into managing DHCP. So what is DHCP? DHCP is the core of network configuration. This is the protocol that is used to assign IP addresses in an automated manner. You can define your address scope, address scheme, as well as additional features for all your workstations and servers in the network using Windows DHCP server. If you did not have any DHCP server, your alternate option would be to assign IP addresses manually to all workstations and servers. This alternate option is literally impossible to do when you have a larger environment or when you have an environment that is constantly changing. So how does DHCP work? The DHCP concept can be broken down into four steps. These steps are known as D-O-R-A or DORA. First thing to remember is that you will need to install a DHCP server that basically gives out IP addresses. Each Windows machine has a built-in DHCP client. This client gets activated when you set the property to obtain IP address automatically. The first step is for the client to broadcast a DHCP Discover packet when it is communicating over the network. A DHCP server will respond with a DHCP Offer packet, which contains potential address for the client. The client receives the DHCP Offer packet and then it sends a DHCP Request packet that contains the server identifier, meaning that it'll send a DHCP Request which contains the name of the DHCP server that it is trying to get its address from. This way the DHCP server will know that this is the chosen server and it'll go ahead and assign the address. This is done so that if there are multiple DHCP servers, it does not create a confusion. The chosen server stores the IP address of the client information in the DHCP database. And then after it stores the information, it'll send a DHCP ACK, which is an acknowledgement. We already talked about installing a DHCP server. You will have to install DHCP server role on the Windows server. You can do that by using the roles and features in Windows Admin Center, or you can add roles and features wizard from the server manager console. You can also use PowerShell command that is displayed in the slide deck to install the DHCP server role. Note that when you install this role, you should use the server management tool if you are managing the DHCP server configuration from the server itself. Otherwise, you have the option to use asset tools to manage the server. After you install DHCP server role, the role must be authorized in active directory before this server is able to lease IP addresses. Note that it is possible to have single DHCP server providing IP addresses for subnets that contain multiple active directory domains. Because of this, you must use a enterprise administrator account to authorize the DHCP server role. In a single domain environment, membership in the domain admins group is sufficient to authorize the DHCP server role. There are network devices that can also act like DHCP servers, meaning it can give out IP addresses. If you are using Windows server as the DHCP server, you should disable the DHCP service from any other server or any other networking devices that are not authorized. This will prevent you from having any issues with IP address conflict. DHCP server can configure more than just IP addresses. They can also provide information about network resources such as DNS servers and the default gateway. Some of it which you can see in this screenshot that I have put in from the DHCP configuration. Here you can see that we have defined the DNS server, we have defined the DNS domain name, and also there router configuration, which is the gateway address. You can also apply these options at the DHCP server scope reservations or class option level. The DHCP client service applies these options in the order of precedence, going from the least specific to the most specific. The orders are server level, scope level, class level, and reserved client level. Let's now look at DHCP scope. A DHCP Scope is a range of IP addresses that are available for lease and that is managed by a DHCP server. Typically, a DHCP scope is confined to the IP addresses of a given subnet. The DHCP scope is defined by the IP address subnet range, as well as the subnet mask that you can see in this screenshot. In addition to that, there are properties that are mandatory in the DHCP scope when you create them. These properties are IP address range, subnet mask, that we already talked about. You can also define exclusions, which lists single addresses or blocks of addresses that are within the IP address range, but will not be available for lease. Exclusions are there so that you can use certain IP addresses for certain devices such as servers or a specific printer or similar type of configuration. Then you will also need to define your lease duration which means how long this lease is effective. And last but not the least, you'll define the options such as your DNS server or router configuration that we already talked about in our previous slide deck. Let's dive a little bit deeper into DHCP scope and reservation. If you want a computer or a device to obtain specific address from the scope range, you can permanently reserve that address for the assignment of that particular device. This is DHCP reservation that we talked a little bit about in our previous slide deck. Reservations are useful for tracking IP address assigned to specific devices such as a printer. To create your reservation, select the scope from the DHCP console and from the action, you'll just create a new reservation. And from the screenshot, you can see that you'll need to define IP address and a description and also a reservation name that makes sense. And you will also define the supported types, whether this reservation is for DHCP or just for BOOTP or both. Let's now dive into DHCP and high availability. DHCP is a critical component and needs to be available when client request IP addressed. That is why high availability in DHCP is so important. There are options for creating high availability in DHCP. These include implementing DHCP failover, which you're going to do from DHCP server configuration. Or you can just do Windows server failover cluster, which is basically creating a Windows server cluster and assigning both modes of the cluster DHCP role. Last but not the least, you can also implement a split scopes type of DHCP, which basically means that your DHCP server A will have a scope that is different from a DHCP server B. Now, this does not actually create a failover type of situation, but at least you have two different servers and potentially you can change the scope if all other prerequisites are met, such as DHCP permissions and required scope. Let's look at how to configure failover. The DHCP failover feature allows the two DHCP servers to work together to provide IP address information for the client. To configure failover, the DHCP management console is used and you will use the configuration failover wizard. Let's look at this screenshot first. So as you can see that you can configure only two DHCP servers in the failover relationship and you can configure this only for IPv4 scopes. To configure the DHCP failover, you have to establish a failover relationship between the two servers and you have to give this relationship a name. You can also configure the failover in one of the two modes which is load balance, meaning that the load of assigning the addresses will be balanced between the two servers, or a hot standby. Hot standby means that you have a primary DHCP server which assigns all the DHCP addresses, and then the other server sort of works as a backup. From our discussion, we learned that DHCP is a key part of any network infrastructure. You need to manage and maintain your IP addresses. Therefore, the automation is always preferable. At the same time, you also want to make sure you have a way to assign important roles like DNS, as well as your gateways and other specific roles can be defined by DHCP. You also want to have a mechanism that can be used to update IP addresses should your scope increase as your organization grows. Last but not the least, you want to have a mechanism to authorize DHCP server. Since we are talking about environments where there can be multiple DHCP servers, as well as we want to be assured that we are maintaining security and security authorization is extremely important and DHCP servers can provide you with that specific feature of authorization. Windows server DHCP server gives you the utmost administrative control that you need in this day and age. We will dive deep into DHCP for hybrid environment in our upcoming videos for this course.