Category: Windows 2000

Windows 2000 Tutorials

Introduction to Active Directory

Certainly the biggest single change between Windows NT 4 and Windows 2000 is the inclusion in Windows 2000 of an important new service – Active Directory. Active Directory is the native directory service in Windows 2000. Unlike Windows NT 4, when domains were pretty much stand-alone islands that we connected with trust relationships as necessary,

Active Directory is a full-featured directory service. But what is a directory service? Well, a directory service is actually a combination of two things – a directory, and services that make the directory useful. Simply, a directory is a store of information, similar to other directories, such as a telephone book. A directory can store a variety of useful information relating to users, groups, computers, printers, shared folders, and so forth – we call these objects. A directory also stores information about objects, or properties of objects – we call these attributes. For example, attributes stored in a directory for a particular user object would be the user’s manager, phone numbers, address information, logon name, password, the groups they are a part of, and more.

To make a directory useful, we have services interact with the directory. For example, we can use the directory as a store or information against which users are authenticated, or as the place we query to find information about an object. For example, I could query a directory to show me all the color printers in the Frankfurt office, the phone number of Bob in the Delhi office, or a list all of the users accounts whose first name starts with the letter ‘G’. In Windows 2000, Active Directory is responsible for creating and organizing not only these smaller objects, but also larger objects – like domains, organizational units, and sites. In order to fully comprehend what Active Directory is all about, we need to take an initial look at a number of concepts. A deeper discussion on Active Directory will be covered once we get to the AD Implementation and Administration portion of the series.

Introduction to Windows 2000 Server

Windows 2000 Server and Professional are fundamentally quite similar, both in terms or interface and architecture. As such, they often get lumped together when discussed, and for the purpose of the exams, this is very much the case. However, there are a number of fundamental differences between the two. The two main differences between Server and Pro are in terms of optimization as well as services offered. Professional is optimized as a desktop operating system where one runs user applications, while Server is optimized to service a variety of requests from client systems. In terms of services offered, Server provides many more than Professional, providing the ability to run WINS, DNS, Active Directory, and so forth. Since we’ve already covered the Professional materials, let’s begin taking a look at what the Server product itself is all about.

First off, we can’t just talk about the Server product, because there are actually three: Windows 2000 Server, Advanced Server, and Datacenter Server. There seems to be some debate over the differences between these three, when in fact the only differences are in terms of scalability and availability.

Be aware that the minimum support CPU for Server is a Pentium 133, and recommended minimum for RAM is 256 MB, although 128 MB is the minimum supported. The scalability elements outlined in the table above are obvious – Advanced and Datacenter Server can utilize more RAM and CPUs than the basic Server version. However, both of these versions also support two types of clustering, which are availability technologies. When servers are clustered, more than one server (called a node) is connected to a common storage device, and work together as a single system to ensure availability of mission-critical applications. Should one of the nodes in a cluster fail, the services are still available, since the other nodes continue to handle requests. In a Network Load Balancing (NLB) cluster, client requests are distributed amongst a number of systems that provide access to a single application. For example, you could have up to 32 servers configured with identical copies of your website, and the NLB will distribute requests across the NLB cluster, increasing performance, availability and reliability. Just a note, but any suggestion that Windows 2000 Server cannot act as a domain controller is absolutely false.

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Subnetting IP Networks

It sometimes amazes me that people get so worked up about subnetting, because it really is quite simple. First of all, you need to recognize that in order to really understand subnetting (at least starting off), looking at the numbers in decimal notation makes very little sense. You need to be looking at numbers in binary to really understand what is happening. The beauty of binary numbering is its simplicity – each value can only be a 1 or a 0. Note that each section (octet) of an IP address can be represented by a series of eight bits. There are 4 octets, so 32 bits altogether. That means any IP address can be also looked at as a 32-bit binary number. The table below outlines binary numbering corresponding values.

Decimal 128 64 32 16 8 4 2 1
Binary 1 1 1 1 1 1 1 1

What this means is simple. If I were to ask for the value of 11001100 in decimal, it would be 128+64+0+0+8+4+0+0, which equals 204. Each bit corresponds to the decimal value above it – add the values for each ‘1’ value and you have the answer. 11111111 would be 128+64+32+16+8+4+2+1, which equals 255 (which is also the highest possible decimal value in an 8-bit binary number).

But what about converting decimal numbers to binary? Well, it’s different, but no more difficult. Start at the left on the chart above, and add the decimal values together until you reach your total. Every number you use is a ‘1’ and every number you leave out is a ‘0’. For example, let’s take the number 77. This would be 01001101. Say what? Well, I just started adding numbers left to right, leaving out numbers that put me over 77. In this example, I have 0+64+0+0+8+4+0+1. Simple.

You can also do this using a calculator program with a scientific mode. Just type is a number in decimal and hit the BIN button. The number will then be displayed in binary. However, the calculator has no idea that you’re dealing in 8-bit numbers, so you’ll have to be careful. For example, my calculator will tell me that 77 in binary is 1001101. That is, it leaves off any leading zeros. As such, you’ll need to remember to ‘pad out’ your binary numbers to 8 bits if you use the calculator. For example, the calculator will show decimal 8 as binary 1000. For an IP address, we need to add the 4 other zeros, making it 00001000. You’ll have access to the calculator on the exam, so know how to use it.

After you understand binary numbering, subnetting is easy. First of all, we need to discuss what subnetting is. Quite simply, it is taking a big network ID and breaking it down into a number of smaller networks, or subnets. Routers are what usually separate subnets. Reasons for subnetting include connecting different topologies (such as Ethernet and Token ring), as well as making networks smaller and more manageable. Subnets are also sometimes referred to as broadcast domains, since a broadcast sent on a subnet goes to all hosts on that subnet

For the purpose of any exam, you will need to recognize and understand how subnetting works. This includes being able to view system configurations and determine why clients are having trouble communicating. As such, you’ll need to be able to recognize valid IP addresses, subnet mask values, and what range of IP addresses are valid on a given subnet. Let’s start with a look at valid subnet mask values.

A subnet mask means little in decimal. In binary, however, they tell a story. The subnet mask is what tells us which of the 32-bits in an IP address represent the network identification, and which represent the host identification. In the example below, the host IP address is 156.77.11.3 and the subnet mask is /21, or 255.255.248.0. In decimal, it is difficult to determine which portion represents the network and which the host. However, it binary the mask value is:

11111111 11111111 11111000 00000000

So what does that tell me? That the first 21 bits are used to represent the network, and the last 11 bits are used to represent a host on the network. Actually, it tells me more than that. It also tells me how many hosts I can have per network. How? Well, if eleven bits are used to represent a host, then this subnet can have 2046 hosts. How did I get that? Simple: 2 to the power of 11, minus 2. That equals 2048 minus 2, or 2046. Why minus 2? You subtract 2 because a host value of all binary 0’s represents the subnet, and a value of all binary 1’s is the broadcast address for this subnet.

If the subnet mask in the example above had been /17, or 255.255.128.0, that would leave 15 bits for host addresses. That would mean 2 to the power of 15 minus 2 hosts, or 32766 total.

Figuring that stuff out should now be easy enough as well. The big question, and the key thing you need to be able to do, is to be able to determine if a host ID is valid on a subnet. Every subnet has a range of addresses that are valid on it. In my last example, there were 32766 valid host addresses. You need to be able to determine which ones are valid for the subnet. It isn’t that hard, but you need to know what you’re looking for.

Let’s say that we’ve been given an address of 156.17.42.6/20, and we’re trying to determine the range of valid host IDs on this subnet. The first step is to determine the actual network ID on which this host falls. The process we use to determine this is called ANDing. When we want to AND an IP address and subnet mask, we first convert them to binary and line the subnet mask below the IP address. Then, calculate the AND value. In an AND operation, values are calculated as follows:

1 and 1 = 1
1 and 0 = 0
0 and 0 = 0

In our example, this would give us:

IP 10011100 00010001 00101010 00000110

SM11111111 11111111 11110000 00000000

AND 10011100 00010001 00100000 00000000

After we convert our ANDed address back to decimal we get 156.17.32.0. This is the network ID that our host falls onto.

Stay with me here. We know that our mask is 255.255.240.0 (or /20). So, we know that the last 12 bits represent the hosts on this network. The network bits are in black below, the host bits in red. We already know that a host ID cannot be all zeros or all ones in binary. So, when I’m calculating the range of valid IPs on this subnet/network, I can’t have either of these values. This leaves me with:

Network ID 10011100 00010001 00100000 00000000

First Valid Host ID 10011100 00010001 00100000 00000001

Last Valid Host ID 10011100 00010001 00101111 11111110

Note that the first valid host ID sets all host bits to zero except the last (called the least-significant bit), and the last valid host ID sets all host bits to one, except the last. What did I lose? Two addresses – the host ID being all zeros (which defines the network) and the host ID being all ones (the broadcast address, which is not valid for a host). These are the same 2 addresses that I subtract when trying to find how many hosts I can have per subnet. If I convert my ranges above to decimal, I end up with a range of:

156.17.32.1 to 156.17.47.254

The truth of the matter is that you won’t necessarily have time to ‘do the math’ for every question that comes at you during the exam, so you’ll need a way to quickly determine what ranges of hosts are valid on a subnet given a certain mask. For this purpose, I am providing the chart below. You can use this chart to quickly determine the valid ranges of IP addresses on a subnet based on the mask value, and where the next range starts. Please do not use this chart as a crutch if you don’t understand how to determine valid ranges as we went through above. This is meant as a shortcut for those who already understand.

Mask 128 192 224 240 248 252 254 255

Network ID 128 64 32 16 8421

How the chart works is simple. Let’s say I’ve been given a host ID of 167.23.87.13 with a mask of 255.255.248.0, and I want to quickly determine the range of host IP addresses valid on the same subnet as this host. This address is subnetted into the third octet based on the mask, so we take the third octet value (248) and plug it into the chart above. The Network value that corresponds to 248 is 8. As such, that means that every new subnet starts at a multiple of 8 in the third octet. For example:

167.23.0.0 subnet0 range = 167.23.0.1 to 167.23.7.254 *
167.23.8.0 subnet1 range = 167.23.8.1 to 167.23.15.254
167.23.16.0 subnet2 range = 167.23.16.1 to 167.23.23.254
167.23.24.0 subnet 3 range = 167.23.24.1 to 167.23.31.254
167.23.32.0 subnet 4 range = 167.23.32.1 to 167.23.39.254
…
167.23.80.0 subnet10 range = 167.23.80.1 to 167.23.87.254
…
167.23.240.0 subnet30 range = 167.23.240.1 to 167.23.247.254
167.23.248.0 subnet31 range = 167.23.248.1 to 167.23.255.254 *

* Although these ranges were usually omitted in a classful IP addressing system, they are