Curs PC si internet cap 11.4 Routable Protocols

11.4 Routable Protocols 11.4.1 Routed protocols Instructor Note The concept of routed protocols is introduced. Without routable protocols, internetworking is impossible. Students should be reminded that all of these discussions of addressing and protocols are layer 3 issues. IP is a network layer protocol, and because of that, it can be routed over an internetwork, which is a network of networks. Protocols that provide support for the network layer are called routed or routable protocols. 11.4 Routable Protocols 11.4.2 Other routed protocols Instructor Note Three important routable protocols, IP, IPX, and AppleTalk, are introduced. By far the most important, since it is part of the TCP/IP protocol stack and the informal "official" protocol of the Internet is IP. The focus of this course is on the most commonly used routable protocol, which is IP. Even though you will concentrate on IP, it is important to know that there are other routable protocols. Two of them are IPX/SPX and AppleTalk. 11.4 Routable Protocols 11.4.3 Routable and non-routable protocols Instructor Note Students may begin to think that all layer protocols are routable, so a counter-example -- the common NetBEUI, is presented. Protocols such as IP, IPX/SPX and AppleTalk provide Layer 3 support and are, therefore, routable. However, there are protocols that do not support Layer 3; these are classed as non-routable protocols. The most common of these non-routable protocols is NetBEUI. NetBEUI is a small, fast, and efficient protocol that is limited to running on one segment. 11.4 Routable Protocols 11.4.4 Characteristics of a routable protocol Instructor Note In order to be routable protocols, IP, IPX, and AppleTalk all have layer 3 addressing schemes in addition to physical hardware addresses. Thus Layer 3, hierarchical addressing, and routing are all intimately related. In order for a protocol to be routable, it must provide the ability to assign a network number, as well as a host number, to each individual device. Some protocols, such as IPX, only require that you assign a network number; they use a host's MAC address for the physical number. Other protocols, such as IP, require that you provide a complete address, as well as a subnet mask. The network address is obtained by ANDing the address with the subnet mask.