use Transmission Control Protocol/Internet Protocol (TCP/IP) as their primary networking protocol. Microsoft is no exception when it comes to supporting TCP/IP in its workstation and server products. All current versions of Microsoft’s operating systems support TCP/IP, as do most other modern operating systems.
An easy way to understand DNS is to think about making a telephone call. If you wanted to call Microsoft and did not know the phone number, you could call information, tell them the name (Microsoft), and get the telephone number. You would then make the call. Now think about trying to connect to Server1. You don’t know the TCP/IP number (the computer’s telephone number), so your computer asks DNS (information) for the number of Server1. DNS returns the number, and your system makes the connection (call). DNS is your network’s 411, or information, and it returns the TCP/IP data for your network.
TCP/IP is actually a collection of different technologies (protocols and services) that allow computers to function together on a single, large, and heterogeneous network. Some of the major advantages of this protocol include widespread support for hardware, software, and network devices; reliance on a system of standards; and scalability. TCP handles tasks such as sequenced acknowledgments. IP involves many jobs, such as logical subnet assignment and routing.
The Form of an IP Address
To understand DNS, you must first understand how TCP/IP addresses are formed. Because DNS is strictly on a network to support TCP/IP, understanding the basics of TCP/IP is extremely important.
An IP address is a logical number that uniquely identifies a computer on a TCP/IP network. TCP/IP allows a computer packet to reach the correct host. Windows Server 2012 R2 works with two versions of TCP/IP: IPv4 and IPv6. An IPv4 address takes the form of four octets (eight binary bits), each of which is represented by a decimal number between 0 and 255. The four numbers are separated by decimal points. For example, all of the following are valid IP addresses:
■ 128.45.23.17
■ 230.212.43.100
■ 10.1.1.1
The dotted decimal notation was created to make it easier for users to deal with IP addresses, but this idea did not go far enough. As a result, another abstraction layer was developed, which used names to represent the dotted decimal notation – the domain name. For example, the IP address 11000000 10101000 00000001 00010101 maps to 192.168.1.21, which in turn might map to server1.company.org, which is how the computer’s address is usually presented to the user or application.
As stated earlier, IPv4 addresses are made up of octets, or the decimal (base 10) representation of 8 bits. It takes four octets to add up to the 32 bits required. IPv6 expands the address space to 128 bits. The address is usually represented in hexadecimal notation as follows:
You can tell that the implementation of DNS would make life a lot easier for everyone, even those of us who like to use alphanumeric values. (For example, some of us enjoy pinging the address in lieu of the name.) Fortunately, DNS already has the ability to handle IPv6 addresses using an AAAA record. An A record in IPv4’s addressing space is 32 bits, and an AAAA record (4 As) in IPv6’s is 128 bits.
Nowadays, most computer users are quite familiar with navigating to DNS-based resources, such as www.microsoft.com. To resolve these “friendly” names to TCP/IP addresses that the network stack can use, you need a method for mapping them. Originally, ASCII flat files (often called HOSTS files, as shown in Figure 2.1) were used for this purpose. In some cases, they are still used today in small networks, and they can be useful in helping to troubleshoot name resolution problems.
FIGURE 2.1 HOSTS file
As the number of machines and network devices grew, it became unwieldy for administrators to manage all of the manual updates required to enter new mappings to a master HOSTS file and distribute it. Clearly, a better system was needed.
As you can see from the sample HOSTS file in Figure 2.1, you can conduct a quick test of the email server’s name resolution as follows:
1. Open the HOSTS file: C: \Windows\Systems32\drivers\etc.
2. Add the IP-address-to-hostname mapping.
3. Try to ping the server using the hostname to verify that you can reach it using an easy-to-remember name.
Following these steps should drive home the concept of DNS for you because you can see it working to make your life easier. Now you don’t have to remember 10.0.0.10; you only need to remember exchange03. However, you can also see how this method can become unwieldy if you have many hosts that want to use easy-to-remember names instead of IP addresses to locate resources on your network.
When dealing with large networks, users and network administrators must be able to locate the resources they require with minimal searching. Users don’t care about the actual physical or logical network address of the machine; they just want to be able to connect to it using a simple name that they can remember.
From a network administrator’s standpoint, however, each machine must have its own logical address that makes it part of the network on which it resides. Therefore, some scalable and easy-to-manage method for resolving a machine’s logical name to an IP address and then to a domain name is required. DNS was created just for this purpose.
DNS is a hierarchically distributed database. In other words, its layers are arranged in a definite order, and its data is distributed across a wide range of machines, each of which can exert control over a portion of the database. DNS is a standard set of protocols that defines the following:
■ A mechanism for querying and updating address information in the database
■ A mechanism for replicating the information in the database among servers
■ A schema of the database
DNS was originally developed in the early days of the Internet (called ARPAnet at the time) when it was a small network created by the Department of Defense for research purposes. Before DNS, computer names, or hostnames, were manually entered into a HOSTS file located on a centrally administered server. Each site that needed to resolve hostnames outside of its organization had to download this file. As the number of computers on the Internet grew, so did the size of this HOSTS file – and along with it the problems of its management. The need for a new system that would offer features such as scalability, decentralized administration, and support for various data types became more and more obvious. DNS, introduced in 1984, became this new system.
With DNS, the hostnames reside in a database that can be distributed among multiple servers, decreasing the load on any one server and providing the ability to administer this naming system on a per-partition basis. DNS supports hierarchical names and allows for the registration of various data types in addition to the hostname-to-IP-address mapping used in HOSTS files. Database performance is ensured through its distributed nature as well as through caching.
The DNS distributed database establishes an inverted logical
