in our previous video we looked at the process of DHCP from the client's perspective but obviously there are a number of configurations that have to be made to the DHCP server itself so in this video we'll look at some of those DHCP configuration settings when a device requests a DHCP address the DHCP server refers to a list or a pool of addresses that are defined within a DHCP scope this scope commonly includes the IP address range that will be handed out to the different devices on the network as well as any addresses that should be excluded from the DHCP pool you also have your subnet mask as part of this scope there are also lease durations so you know exactly how long these IP addresses will be available on that device and there's other options that you might include such as the DNS servers that need to be configured default gateways and other additional optional settings such as Voiceover IP server IP addresses there are usually a pool of IP addresses created on a per subnet basis and each scope usually is responsible for providing that particular subnets IP addresses usually this is a contiguous pool so you could tell the DHCP server to assign addresses 1 through 100 on this particular subnet and then if you want to create exceptions to that you can add them to the scope as well here's what this looks like on the server manager on Windows Server this is part of of the DHCP server settings and this particular DHCP server handles the network sg1 SGC dolo you can see there is a single scope available on this network its scope is 16524 44.0 and within that scope you have a pool of IP addresses that would be handed out the address leases any reservations in this IP address range reservations are for devices that will always receive the same IP address each time it is requested and then a scope options that you might include along with others on this scope so if you need to make changes to the IP address pool or modify any of the DNS configurations or anything else associated with DHCP you would do that all from this DHCP settings inside of this scope on the server this process happens automatically for the inst stations they make a request to the DHCP server and the server goes through the pool of addresses picks one one of those addresses and hands it out to that device on the network there's a lease period associated with this address so that device is able to use that IP address for only a limited amount of time and if that lease is not renewed that address is then returned to the pool and someone else visiting that Network can potentially be assigned that IP address an interesting feature of DHCP is that it will keep track of these Mac addresses and IP addresses that it's pairing together so if you visit this network again the DHCP server will recognize that you've been here before and if the IP address you used previously is still available in this pool you will be assigned the same IP address you had on your original visit if you wanted to configure an IP address on a printer or a server and you wanted to confirm that that IP address would never change you could manually configure those settings on that device but this does not scale very well especially in large networks and if you need to make a change to those settings you need to manually visit all of those devices to make that configuration update instead you might want to lock in the IP addresses for those devices in the DHCP server using a feature known as address reservation inside the DHCP server you would create a table that has the Mac addresses of these devices such as your printers and your servers and you would manually configure an IP address within the DHCP server that will always be assigned to that particular Mac address if you look at your DHC P server you might see this listed as static DHCP assignment static DHCP or an IP reservation here's the address registration process in one of my DHCP servers this one has a couple of reservations that I've added this one is 192.168.1 6 the device name is Prometheus and you can see the MAC address of that device is listed in the reservation I also have another IP address 192.168.1 n this is the device known as Odyssey and it has of course a different Mac address by adding these addresses into the DHCP server as a reservation I can go to one central place to manage all of this information yet still be assured that those devices will always receive the same IP address every time they're started as we mentioned earlier these DHCP addresses are not permanent they are leased to these devices and they're only available for a temporary amount of time this lease time is one that is configured in the DHCP server itself in some organizations they might have a very long lease time in other locations it might be very short you as the DHCP administrator get to determine what the least time will be for your network if you were to look at the IP address configuration of your device you would see the lease timer associated with the IP configurations if you were to restart that device or unplug from the network and plug back in again you would be reinitializing that DHCP process and potentially restarting that lease another nice feature of DHCP is if you are turning off your system it can release that IP address back into the pool so that other people would be able to use that IP address in the future this DHCP leasing process doesn't wait until the entire lease is complete before trying to renew the lease instead there are different timers that DHCP will use to be able to provide that renewal the first timer is a T1 timer this is set by def fault as 50% of the lease time so no communication is going to occur between your device and the DHCP server until half of that lease is complete at which time your device will attempt to communicate to the DHCP server and renew the lease but it could be that the original DHCP server is no longer operating properly or has been removed from the network in that case we go to a T2 timer by default the t2 timer is 87.5% of the lease time or 7/8 of that lease time with the t2 timer your device will attempt to renew the lease with any available DHCP server that's on the network let's say on your network that your DHCP server is set with a least time of 8 days if we do the math that means the T1 timer since it's 50% of the lease time would be 4 days and the t2 timer or rebinding timer would be 78 of that time frame or in this case 7 days so under normal operation we'll go along for 4 days without needing to check in with the DHCP server but as soon as we hit that T1 timer we're going to begin a period where we will begin renewing with the original DHCP server so that renewal is sent to the server and if that DHCP server is available it will very quickly renew that lease and we'll have another 4 days where we can continue to operate without checking in again with the DHCP server but let's say at this point that DHCP server is taken out of the network and is no longer available that means we will go all the way through the renewal period without ever renewing the lease once we hit the t2 timer or the rebinding period your device will reach out to any DHCP server to try to renew that lease and on your corporate Network there's most certainly another DHCP server and it will renew that lease and the entire timing process starts over again we often think of DHCP as that automated IP address subnet mask and default gateway configuration but there are other options that DHCP can configure as well and we refer to those literally as DHCP options this is a separate field in the DHCP process that allows us to configure other settings that are related to tcpip these options are listed in the request for comments or the RFC associated with DHCP back in the bootp days we refer to these as vendor extensions these DHCP options are associated with a number and there are 254 usable options that could potentially be configured using DHCP the common configurations for DHCP would be the things that we would normally think about the IP address the subnet MK the default gateway and the DNS servers and there may be times when you would like to add additional DHCP options to be configured on that device but you have to make sure that the DHCP server supports that specific option not all DHCP servers support the ability to configure DHCP options so you'll want to check with your DHCP server to make sure that the options you need are supported by that server for example you might have a Voiceover IP call server on your network and you might want to add that as part of the DHCP configuration process so option 129 is the DHCP option for the call server IP address if you wanted to configure an HTTP proxy you would use option 135 and are many other DHCP options to choose from we're looking again at the scope that's configured within Windows Server under the dhtp server options and there is an option there for Server options and that refers back to those dhtp options you can see a list of all of the numbered options within those server options you can select any of those and Define them within the DHCP server itself then when anybody connects to the network not only will they receive the IP address subnet m default gateway and DNS settings they'll also receive any of the configurations that you've defined under DHCP options