2.3 Select the appropriate network and transport protocol or protocols for various token-ring and Ethernet networks.
DLC: Data Link Control. You dont need to know how DLC works. For the Networking Essentials exam, you should remember four things:
Some tricky questions regarding DLC as following:
If you have a PC only has NetBEUI installed, if you don't have any other software installed, what kind of networking device can you use to connect IBM mainframe?
Please note that DLC is not the correct answer for this question! Although we can use DLC to connect IBM mainframe, it only means that we connect the machine directly to the IBM mainframe while not over the network. In most cases, you can use serial ports to connect the IBM mainframe and your machine works as a terminal for the mainframe. The correct answer for above question is the gateway, which we will discuss later and it provides protocol converting over the network.
AppleTalk is a network protocol from Apple Computer, Inc. It is built into the Macintosh computers. AppleTalk supports Apple's proprietary LocalTalk access method as well as Ethernet and Token Ring. AppleTalk is a routable protocol and works on both the transportation and network layer such as TCP/IP and IPX/SPX.
IPX/SPX (Internetwork Packet Exchange/Sequenced Packet Exchange) is a NetWare communications protocol from Novell. IPX/SPX is routable just like TCP/IP. IPX is like IP that works at Network layer, and SPX is like TCP that works at Transport layer. But IPX/SPX is smaller and efficient than TCP/IP.
For the questions such as FTQ 2.3.2, if NetBEUI is not one of the choices, you can select IPX/SPX to connect several PCs and build a small network. For the Networking Essentials exam, IPX/SPX protocol has different frame types, only when the client and server has the same frame type, they can communicate. When you have multiple frame types on the network, you generally need to reconfigure the frame type manually. This kind of frame type problem only happens on IPX/SPX, none of NetBEUI or TCP/IP has the similar problem.
NFS: Network File system, a service for distributed computing systems which provides a distributed file system, eliminating the need for keeping multiple copies of files on separate computers. By the above definition, you should know NFS works at application layer. Because NFS only supports TCP/IP, implementing NFS requires that the TCP/IP must be preinstalled.
SMB: Server Message Block is a file sharing protocol designed to allow systems to transparently access files that reside on remote systems. It works at presentation layer of the OSI model. To prepare for the MCSE exam, it is not good enough to know the definition. One needs to think it over more carefully. For example, you may be asked to name an upper level protocol that is based on NetBIOS and provide file sharing. Some people might consider the NetBEUI first while not the SMB because they thought that NetBEUI is NetBIOS related.
It is true that if you install the NetBEUI on the network, you can share the file easily. However, please note NetBEUI only works at transportation layer, it is just a general protocol as TCP/IP or IPX/SPX. TCP/IP doesnt provide any file sharing, in order to share the file, you need to install NFS, which works at application layer. Same thing happens for NetBEUI, it doesnt provide the file sharing directly. Therefore, the correct answer is SMB, which works at application layer.
Q: QUE's Networking Essentials Exam Guide book, by Dan York, says SMB is a presentation layer protocol. Why you consider it as an application layer protocol?
Answer: Sometime it is difficult to find one protocol on which layer, because many protocols are not following the OSI model. They focus more on the functions while not the OSI model. It is always true that if it works, no one care which OSI Model it residents. In fact if you search all Microsoft's documents, you will find that Microsoft NEVER mentions the exact layer where the SMB protocol residents. Microsoft just considered SMB as an upper layer protocol. If you can understand this, I think it is enough for the Networking Essential exam. Also take a look at following diagram. When people talking about the Internet protocol, people merge Application layer, Presentation layer and Session layer together and call it the application layer. So sometimes when people mention an application layer protocol, it might corresponds to the Session layer or Presentation layer on the OSI model. I've studied the definition and the functions for SMB. I think SMB has more relationship with the Presentation layer. However, I've checked MS Press book (2nd Edition) on Networking Essential and found in that book SMB is classified as an application layer protocol. Hope Microsoft will not test you this question, but if they test you, I suggest you choose Application layer as the correct answer.