>My intention of creating this thread again was just to clarify things as >some of us concluded that BGP,RIP,OSPF are at network layer. >Why I quoted the stuff in capital and if it hurt some of the members ,I am >sorry but it was just to highlight that this is given in Cisco Press book >and whose author is CCIE and ofcourse reviewed by Imran Qureshi Program >Manager from Cisco on CCIE series of books. > >So again is it right that > >1)RIP,BGP are at application >2)OSPF is at Transport layer >
If Jeff said this, it is wrong. Simple as that. Even if the logic were that anything that runs over layer (N) must be layer (N+1), that would put RIP and BGP at Session, and ISIS at Network. The original OSI model defined in ISO 7498 was published in 1984 and did not contain routing protocols at all, nor did it contain connectionless communications. But if you really want a model: The Seven Deadly Layers By Howard C. Berkowitz Among the most frequent questions I'm asked in OSI teaching is, "Do I need to know what all the layers do?" This is especially true of management audiences, who "need to know" the power centers. (They may not know what a layer is, but they know there are seven of them and they don't want a single one to go unsupervised.) Over the years, I have found a useful analogy. Educational theory suggests we should start with something that the student knows and build from there. Therefore, I ask management audiences to reflect not on theoretical network architecture, but on sin. Specifically, I ask them to consider the Seven Deadly Sins (Note 0). These sins have definite relevance to the OSI Reference Model. The "most popular" deadly sins are analogies for the layers most important for non-developers to know about. Audiences think of sins in a fairly consistent way. Approximately 75 percent immediately think of Lust. Lust, clearly, relates directlyto the Physical Layer. It is essential to be aware of the function of the Lust Layer, for that defines how to "plug in." (Note 1) Most of the remaining audience split between Avarice and Gluttony. These also are important in OSI. Avarice, or Greed, is often realized as the Bottom Line in business. One is closer to understanding the Tao of OSI when one realizes that it places the Bottom Line (i.e. what OSI does for real user applications programs) on Top. The top of the Avarice Layer is the Service Access Point to the Application, or Avarice, Layer. ([Note 2) Those members of the audience who thought first of Gluttony also have some understanding of OSI. Gluttony deals with establishing a relationship between a mouth entity and a food entity. Network deals with the next course while Transport deals with the end goal of dessert. Users really need to know the functions of Application, Transport/Network (as the distinction blurs here), and Physical. They often also need to know the characteristics of the data link layer. Since Data Link has to deal with collisions, master/slave relationships, etc., it may correspond to the sin of Anger. I tend to associate the sin of Pride with the Presentation Layer, on the grounds that Presentation is rather prideful to think that it justifies its own layer. There is always one in the audience, however, who thinks of Sloth. Sloth is a difficult sin. How does one confess it? "Bless me, I have slothed?" "Forgive me for committing sloth?" How can I commit not doing something? Since Sloth is a sin we really have trouble talking about,and involves not doing useful things, it is a relevant analogy to the Session Layer. Both Sloth and Session are needed for theological completeness, but their relevance to the ordinary sinner or the OSI user is fairly limited. [Note 4] If we were to redesign the OSI Reference Model today, its exact number of layers would be controversial, but it would almost certaily not be seven. The flight from sevenness is seen in Internet usage and in the more obscure (but useful) ISO Technical Report 10000 taxonomy for defining protocol stacks (i.e., International Standardized Protocols). Internet practice does use layered protocol stacks, but these rarely have seven layers (Network File System is an exception). Typically, an application service such as File Transfer Protocol (FTP) includes the functions of the top three OSI layers, and in turn layers on top of TCP, a Transport layer protocol. TCP, in turn, layers on top of IP, a network layer protocol. IP runs over a generic Interface or Hardware layer that include Data Link and Physical layers. In like manner, OSI stack specifications have a top A- or B-specification that defines a particular set of Application, Presentation, and Session protocols and their options. The A- or B-profile runs over a lower layer stack definition, the first letters of which identify the transport and network protocols in use, followed by numbers referring to the data link and physical layers. While little known outside OSI circles, this ISO 10000 methodology is useful as a notation for many multilayerd protocol stacks. (Note 3) Research funding is being sought to evaluate the possible relevance of the Seven Dwarves to OSI. (Note 0) Just as there are many theological interpretations in religion, this is not the only interpretation of "sevenness" and OSI layering. David Piscitello independently presented a different mapping of sins to layers in the early 1980s. A Mark Russell presentation gave the author insight on the meaning of confessing sloth. (Note 1) When presenting these analogies at an IEEE conference in New York, a woman's clear voice rang out from the back of the room. "Well, I'm glad SOME standards body is defining how to plug in things correctly. God knows most male engineers don't understand that at all." (Note 2) This part of the analogy can continue into Application ServiceElements: ACSE (the Avarice Control Service Element), ROSE (the Remote Organization Submission Element), etc. (Note 3) After their first reading of Presentation Context Negotiation and ASN.1 Basic Encoding Rules, some nominate the sin of Pride as the proper analogy for the Presentation Layer. (Note 4) Session actually does useful things. The widely used Remote Procedure Call (RPC) protocol, which underlies NFS, is a pure session layer protocol. NetBIOS, as distinct from NetBEUI, also essentially is a session layer protocol. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=21248&t=21226 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]