As mentioned previously, the NetBIOS naming system originally was defined by the Sytek Corporation for IBM, for use on personal computers. It is a flat naming system with names that cannot exceed 16 characters. Although RFC1001 defines 16 characters for a NetBIOS name, Microsoft uses the sixteenth character as a NetBIOS suffix to define various functions, as you'll see in a moment.
By contrast, DNS is a more flexible system because names are not constrained by the 16 character limit. It is a hierarchical system, which allows for both longer names (up to 255 characters) and a more orderly method of naming. In addition, DNS has the ability to distribute and update a name resolution database across a WAN to provide more efficient name resolution services.
Remember that Microsoft NetBIOS names are limited to 15 characters even though RFC 1001 allows for 16. In Microsoft implementations of NetBIOS, the sixteenth character is a NetBIOS suffix. Keeping this in mind will help you identify illegal NetBIOS names on the exam.
The NetBIOS construction is a flat naming system.This means that only one computer can have a particular name, which must be unique on that network (or on any network to which that network is attached). Examples of a flat naming structure are SERVER1, SERVER2, and SERVER3. Under such a flat system, if Company A, connected to the Internet, had a server called SERVER1, then no other company connected to the Internet could have a server called SERVER1 or data packets would not be properly delivered to either computer. Clearly, this becomes a constraint very quickly, especially because all companies cannot possibly check with one another before naming a computer and bringing it online.
The hierarchical system, used by DNS, is a more flexible system that still guarantees a unique name. In this framework, the naming system is called the domain namespace and is structured similarly to a directory tree on a disk drive. In this system, the domain namespace begins at the root, which is unnamed and is identified by "."As it expands, there are more and more branches to the tree and each node creates a unique name. An organization can choose to create a private domain namespace and it does not have to be unique as long as it does not interact with public networks such as the Internet.
If you're like most people, the first time you encounter some of the naming conventions in the computer world you can become quite confused. It seems there are names for everything but none of the names are quite the same. Let's take a moment to go through some of these to help answer any questions you might have.
■ Computer name A computer name is just that, the name you give your computer. In many companies this name is assigned, although in some companies users can choose their computers' names. On a Windows XP/2000/Server 2003 computer, you can find your computer's name by right-clicking on My Computer and selecting Properties. (Alternately, you can select System from Control Panel to access the System Properties dialog box.) Then click the Computer Name tab to display (or change) your computer name. If you're on a network, this name must be unique. If you're not on a network, this name can be just about anything you choose.You can configure alternate names on the Computer Name tab by clicking More and entering your particular data. However, changing this information on a computer already connected to the network can cause the computer to lose connectivity due to naming conflicts. Most companies use a naming scheme to ensure all computer names are unique.
■ NetBIOS name In a Windows-based computer, the name you see listed on the Computer Name tab of the My Computer properties is the NetBIOS name.This name can be up to 15 characters long (in Microsoft operating systems) and is used to identify the computer on the network. When NetBIOS name resolution occurs, the computer name (NetBIOS name) is mapped to an IP address.
■ Host name This term originates in the mainframe and UNIX world. It was originally used in the same way a computer name is used in Windows. Technically, a host is any device with an IP address that is not a router and that is attached to the network. Host names are used in DNS and are resolved to IP addresses. Although host names are resolved to IP addresses as are NetBIOS names, the resolution process is different—do not confuse these two types of names. NetBIOS names must be resolved via an LMHOSTS file or via a NetBIOS name server, which in Windows is implemented as Windows Internet Naming System or WINS. Host names must be resolved via host name resolution, which is accomplished via a HOSTS file or via DNS servers, requesters, and resolvers (you'll learn more about this later in this chapter).
A host name can be up to 255 characters long and can contain alphanumeric characters and the hyphen symbol (-). A period is used as the delimiter between segments in a DNS name, so it cannot be part of the name. Blank and space characters are not permitted. The first character, until recently, had to be an alpha character. That limitation has been removed and names can now begin with an alpha or numeric character. The last character cannot be a hyphen (-) or period (.). Case is not relevant, thus there is no difference between the names SERVER, SERver, and server.
Some Microsoft documentation incorrectly states that the dot (.) character can be used in host names. This is incorrect and will result in errors. The dot character is interpreted as a delimiter and can be used in Fully Qualified Domain Names (FQDN). For more information, see Microsoft Knowledge Base article 122900.
By default, a computer's host name is set to the computer name (also known as the NetBIOS name), but a different host name can be assigned to the computer. To see the computer's host name, you can use the command line by choosing Start | Run and typing cmd. In the command prompt window, type hostname, then press Enter. The computer's host name is displayed. To compare it to the computer's NetBIOS name, use the command line again and type net name and press Enter. The computer's NetBIOS name is displayed (along with the logged on user's account name).To close the command prompt window, type exit and press Enter. Type the word exit to close the command prompt session.
■ DNS name A DNS name can be a series of labels, each separated by a dot (.) to distinguish branches or nodes of the name within a hierarchy. An example of a DNS name is rosie.security.az.somecompany.com.When displayed in this manner, the name is called a Fully Qualified Domain Name (FQDN) because the entire path is shown.The left-most segment of a DNS name is the specific host name of the device; the remaining segments are the domain name (left to right from lowest to highest level domain).
■ Nickname A nickname is an alternate name given a host name. It is often a shorter version of the FQDN. For instance, the computer named rosie.security.az.somecompany.com might also be called rosiel. As long as this nickname is unique on that node, the nickname can be used to map to the FQDN, which is then used to map to the IP address. In this case, rosie is the actual host name and rosiel is the nickname. However, if another host is named rosie, it cannot also be called rosiel. Another host can be named rosie if it is on a different node, however. For instance, rosie.security.fl.somecompany.com is not the same name because it follows a different path. However, it cannot use the nickname rosiel. But it can use the nickname rosie2.You'll learn more on this topic throughout this chapter.
■ Alias An alias is a any name used in place of another name. In DNS, an alias is called the Canonical Name (CNAME). A server named serverl.somecompany.com might have an alias of dcl.somecompany.net, for example.You'll learn more about this later in this chapter, and we'll discuss how and why aliases are used.
It is important to understand how NetBIOS names are resolved to IP addresses in order to understand the similarities and differences between NetBIOS and DNS naming conven-tions.We'll review NetBIOS name resolution briefly here.
A NetBIOS name can be l6 characters long, but in Windows, the sixteenth character is reserved for various NetBIOS functions. If a name is not l5 characters long, it is padded with spaces (in binary format, with 0s) so that all names are always l5 characters plus the sixteenth function character. The sixteenth character is used by Microsoft networking to define functions installed on the named device, such as Workstation Service, File Server Service, Master Browser Service, and so on. Several of the more common NetBIOS suffixes are shown here. The name type is shown with the hexadecimal (hex or h) suffix. They're shown in hex format because some of the characters are not printable.
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