Configuring DHCP Scopes


Windows Server 2012 Core Technologies

Configuring DHCP Scopes

Instructor: Rick Trader
Duration: 17 Hours
Video Style: Classroom

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Video Transcript:

Dynamic Host Configuration Protocol DHCP‑‑ scopes and scopes options. In this video, we will be looking at what a DHCP scope is and how to configure it. We’ll be looking at what DHCP options are, what options we should configure and how do we got back configuring them. We will be finishing the video looking what a DHCP reservation is, when we should use reservations, and how reservation can be configured.

[0:36] So starting up with what is a DHCP scope. Thinking of scope as a pool, a pool of IP addresses that a DHCP server can handle or server can handle IP addresses for an individual network segment or it can actually handle multiple network segments. So I can have one DHCP server handling IP addresses for different segments or refer to DHCP scopes.

To configuring the action DHCP scope is we will go into a DHCP server and we actually put on the DHCP console a couple of different ways. What are the ways to bring the DHCP console would be to go into Server Manager. Under TOOLS, we have a DHCP server.

[1:23] Notice that also under notification area, we have a prompt saying our DHCP has been installed but is not being configured so we can actually watch complete DHCP configuration here and it would bring DHCP console.

The other way to bring up the console would be from the actual desktop typing DHCP and are also launched through the smart search, the DHCP console. So whichever way you want to bring the console up is up to you.

So I expand my server. Expand IPV4. Once I expand IPV4, I have an option to configure server options, policies and filters. We’ll discuss each one of these items a little bit later.

[2:09] When I right click on the IPV4 options, I have an option to create a new scope. In previous versions of the DHCP Server Service whether it be Windows 2000, 2003 or 2008, 2002, there was an option to create a superscope or a scope so that I could go in if I were doing supernetting, I could actually use DHCP to configure a scope that could cover more than one network segment.

In Server 2012, they’ve removed the superscope option. We still have regular scope and multicast, and we’ll talk about multicast here in a little bit.

If I click on new scope, it’s going to launch a wizard for us. I click next and I’m going to give the scope a name. Traditionally, when I name my scopes, I’m going to name either the logical location or the geographical location for the scope and I usually put in also where the scopes IP addressing range is going to be.

[3:09] So I’m going to call this Phoenix and I’m going to make it 172.16.10.100‑199. So this is the range of the IP address that I’m going to be issuing from this DHCP server.

I hit next, I then get asked what my starting IP address is for the range 192.168.16.100 and I can do one of two things. If I come in and I do my subnet mask 192.168, this should be 16 not 160, and actually get rid of that.

[4:05] My fingers aren’t wanting to pay attention today. 10.199. Notice I’ve written down my subnet mask. It already alters it here. Also, if I just type in here, 255, notice it doesn’t change the subnet myth, but watch very quickly and closely. If I hit next, it will actually switch the length from 17 to 24. Then, I can put in an exclusion.

So, what’s an exclusion? Let’s say, for instance, I have a range of IP addresses, 172.16.10.100 through 199, and right in the middle of that range I have a static IP address I know is configured. I can exclude that IP address from being handed out by my DHCP server.

[4:57] If I have a single address, 172.16.10.150, let’s say, and it’s also 172.16.10.150. I’m excluding one IP address. If I have a range of IP addresses, I would start the beginning and the end IP addresses, and I click add.

Let me go back here real quick. I realize this should be 172.16, and now when I add my exclusion in, right, it adds the entire range of 150, 151, 152, 153, 154, 155 from the addresses being handed out.

[5:51] I can also have my DHCP server actually wait for X amount of milliseconds before it responds with an IP address.

When we were doing fault tolerance and we had multiple DHCP servers that had IP addresses for the same segments or we can use the delay. In this situation here, I only have the one DHCP server, so I will not be putting in a delay.

[6:13] I hit next, I get asked for my lease. So, the question comes up is, "How long should my lease be?" In Windows 2000, the default lease was three days. In Server 2003, Microsoft made the default lease eight days. So, the question is, right, "When should I up the lease or lower the lease?

The basic guidelines are, if I have more clients than I have IP addresses, I want to shorten the lease. If I have more addresses than I have clients, then I want to lengthen the lease.

[6:44] In this case, I’m going to leave it eight days. Hit next. At this point, I don’t want to configure any DHCP options. I hit next. I hit finish. My DHCP server has now been configured for it to hand out IP addresses in the 172,16,10.100 to .199 range and excluding IP addresses 172.16.10.150, 51, 52, 53, 54 and 55.

One thing I want you to take note, my DHCP server, the scope itself has not been activated. The reason why the scope didn’t activate was because I did not configure any scope options. If I configure scope options during the actual creation of the scope, it will automatically come up as an activated scope. In this case it’s not activated.

[7:36] To activate the scope if I wanted to hand out IP addresses right now, I could right click and choose activate and I would start handing out IP addresses. Now this DHCP server is now handing out IP addresses for again 172.16.10.100 through 199 minus the six IP addresses I excluded.

Scope options or DHCP options. There are really four different types of options I can configure. The first scope option I can configure is considered a server option. Sometimes you’ll read it in books as a global option.

[8:12] A server option is an option I can configure that no matter what network segment you’re in, no matter what scope you’re in, you’re going to get this configuration handed out to you.

The most common things that we put into a server option would be DNS addresses, Win server addresses, DNS name space addresses, would be the types of things that might be in a server option ‑‑ unless, of course, we had a DNS server or a Win server that was specific to a network segment.

Scope options would be the next thing we configure. Specific things that would be to a scope would be gateway, or router. If I configured a server option as a gateway, when I configure it for multiple segments, I’ll have computers that aren’t in the same segment as my DHCP server is in, will not be able to get out to the Internet or get through network segments because of the scope option would be off. So I would want to set a router segment for that, and I’ll show you in a moment how to set that.

[9:13] We have class options. One of the things that Microsoft has done in the DHCP server, is I have the ability to create IP scopes for a specific classes. It could be things like a BOOTP‑enabled class, so that if this computer is getting this IP address over a BOOTP‑enabled router, or through a DHCP relay agent, I could have specific options being handed out for that machine. Or, if I’m getting the IP address through an environment such as a ATM or frame relay, or packet switching, I could have it configured that way.

I can also configure it based off of gender class, Microsoft options, non‑Microsoft options, and so forth. I can also set in options specifically for reservation. We’ll need an IP address given out to a computer that has a specific MAC address, I can set a reservation for that.

[10:05] When I’m looking at these particular options, if I have something configured in all four options, if I take this from top down, looking at it from top down, server options applied first, scope options applied second, class options applied third, and then reservations are applied forth. Just like if I paint a wall. If I paint a wall blue, then I were to paint it red, green then red, if I were to paint it the green, this color here would prevail. It would be the color taken last. Whatever option is being applied last will always win.

Some of our common options. The most common option we’re going to configure in a DHCP server is the gateway, DNS, and Wins. Those are the most three common options that get configured in a DHCP scope. So let me show you how to configure these options.

[11:06] If I bring back up my DHCP server, and I’ve got my scope here, if I want to configure a server option, let’s say, for instance, I don’t care what network segment you’re in, I want you to get the following DNS server address. I’ll come down to server options, right click, configure options, and I can scroll down to option number six.

Now, the question always comes up, that we have is, we have option five name servers, and option six DNS servers. Well, what’s the difference? A name server is a DNS server.

Depending on what the operating system that you’re running is, some clients may not recognize what option 006 is, so they will be looking for option 005 for the DNS server. Some clients may not understand what option 005 is, and be looking for the DNS server as option 006. So you have to know what clients you have in your network segments, to determine whether or not we’re going to use option 005 or 006. Microsoft uses option 006.

[12:06] So I’ll come in, and I’m going to put an IP address in. I’m going to use 4.2.2.2 which is a public IP address of a public DNS server, it’s located on the east coast, and I click add. One of the things it’s going to do is it’s going to automatically go out and see if it can verify that IP address as being a DNS server.

If this was our corporate DNS server, it would go out and resolve the name to that DNS server. Notice it comes back and says I can’t resolve the address, do I still want to add it? I’m going to say yes, because this particular DNS server is announcing itself as a DNS server service, so I went ahead and put 4.2.2.2 and I hit OK. I’ve now configured that server to be a DNS server for all scopes.

[12:53] Let’s say, for instance, though, in this particular scope, I want to use an in‑house DNS server, or I want to use a DNS server that is not what I want to use for everybody else. If I right click, we can do configure options again, I can come down, I can highlight the 006 again, and I’ll put in 4.2.2.3, which is also another public DNS server. Again, it’s going to go out and resolve. After it resolves, in this case, I’ll get an error that it didn’t resolve. Hit OK.

One of the things I want you to take note of is when I configured it as a server option, my server has it as a…it actually shows up as a server with a real page next to it. When I configured it as a scope option, notice the icon changed. It looks like a sheet of paper. In previous operating systems, a server option always looked as gears, and the client options looked as just a computer.

[14:09] So let’s come in and now say on our scope, I want to configure my router, or my gateway. Again, I can have it resolve by name, or in this case my router is 172.16.10.1. Click add, click OK.

Again, one of the most common things that we’re going to set as a scope option will be the IP address of a router. Notice if I were to set the router option up here, it still filters down into all the segments.

[14:56] Let me show this as an example. Let’s say I have another scope here. Let’s call this the Flagstaff scope. It’s 172.16.11.100 through 199 ‑‑ 172.16.11.100, 172.16.11.199. Give it 24 bit. Next, Next, Next.

This time I will configure the scope options as I go through. Next.
The IP address of the router, 172.16.11.1. I’m not going to configure DNS. I’ll leave it as it was before. Next.

[15:59] Notice that I have an option to activate the scope this time. The scope came up as activated, 172.16.11.1. If I come down, I look at scope options. Notice that I now have my scope from…My DNS server came down from the actual…Let me remove this. The DNS server will come down from my actual server options, so when it comes down, you’ll see it as a server icon.

Configuring scope options is fairly easy, and server options…Again, if server options are configured and scope options are configured, scope options will prevail over the server options.

[16:46] Reservations. What if I have a service in my environment that can work on a DHCP‑assigned machine or we decide we want to have DHCP‑assigned IP addresses because we want to have our DHCP server be enabled to do a record keeping for IP addresses, but I have a machine that requires to have the same IP address every time, and I don’t want hand it out to somebody else?

I can assign an IP address from my scope of addresses as a DHCP reservation. To configure a DHCP reservation, I come through the scope I want to configure the reservation in. Right‑click, New Reservation. I’ll give the reservation a name.

[17:33] The most common thing here is, I will want to make the reservation name based off this server I’m giving it to, or it could be a service. I’m going to give this to my USSHQ SRV4 computer. I’m going to give it an IP address out of my current scope of 10. So, 172.16.10…I’ll give it an IP address of, say, 120.

Here is an issue. Remember, I put an exclusion of 150 through 155? This will allow me to give a reservation of 154. The problem with this is, even though it’ll allow me to do the reservation, that IP address will never, ever be handed out, because I excluded it from the DHCP scope from being handed out. I want to make sure, if I want DHCP Server to hand it out, to give it an address out of the segment.

[18:27] I then come in. I’m going to put in a MAC address in. I’ll go 20…Remember, MAC addressees are 12 characters, and they’re hexadecimal. FB‑12…and I’ll do a 10‑EC‑14.

Where do you get the MAC address? This is where you have to have access to the computer or access to the documentation of the computer.

You use the MAC address for the network adapter card you want this IP address to be given. I’ll use it for both DHCP and BOOTP.

Hit add and hit close. I’ve now configured a reservation for this computer for an IP address of 120.

[19:10] Notice it picked up the scope options from the server. I can actually come in here and I can change these options to be specific for this client.

If I come in, let’s say, for instance, the machine’s network adapter card has failed, and I want to change the network adapter card out. When I change that network adapter card out, the MAC address will change.
Notice I can now change the MAC address. What I cannot change is the IP address being assigned by this reservation.

[19:40] So if I want to change the IP address for the reservation, I have to actually create a new reservation.
So I hit OK. Now I’ve created a scope of IP addresses. 172.16.10. I’ve created a server DNS option. And I’ve configured a router option for my machine.

So I’m going to go ahead and minimize this and I’ve got a Windows eight computer here that is a DHCP client. So I’ll go ahead and log into it.

[20:21] It’s currently in the same segment as my environment is, so I’ll do a command prompt.

I’ll go ahead and launch it with administrative rights.

Do a IPCONFIG, and right now, it should have, right, it must have picked up the IP address at 172.16.10.101. It actually didn’t pick up the gateway. That’s because it’s picked up the IP address before the actual gateway was configured.

If I do a /all, right, notice it picked up the DHCP server, but it did not pick up my DNS server address. So come down, I’m going to do a release, and then do a renew, and notice it picked up my gateway. If I do a /all again, and I scroll up, notice it picked up the DNS server and it picked up the fact that TCP/IP over NetBIOS has been enabled and this is also where I can get this machine’s MAC address if I want to give it a reservation. Right.

[21:41] So in this video today, you’ve seen what DHCP scopes are, how to configure a DHCP scope. We’ve looked at how to configure the DHCP scope options and server options and what option overrides when we have conflicts. We’ve also looked at how to create reservations.