Now, now... the OSI model DOES have a purpose. It is a reference model - the key word being "reference".
It isn't the model so much as the fact that it makes it alot easier to look at the various processes discretely rather than as a whole. The OSI model gets you used to the idea that a "process" is actually multiples processes that are hierarchically dependent (more or less). When one of those little processes breaks down, you have a better idea of where to look. Its like knowing that coughing is generally a sign that the problem is with those funny sacks in your chest that pump air, not the entire body (depending on other symptoms of course). I've never felt that is any use knowing that a specific protocol "belongs" to a certain layer. Its far more useful to know that a specific protocol performs X duties and that those duties depend on other things being done by something else. The OSI model just gives you a way of keeping those duties/processes in their proper perspective, as parts, not the whole. just my 2 cents... Karen *********** REPLY SEPARATOR *********** On 12/13/2001 at 10:57 PM Chuck Larrieu wrote: >I once had an interesting, if heated argument with someone off list about >this. IIRC, I was told by that person that Cisco, in its current CCNP study >materials, is saying just that - that something operates at the OSI layer >above which it functions. I.e. if a routing protocol uses an IP protocol >number, then it is operating at transport layer. Since BGP uses TCP port >179, it is operating at the session layer, along with RIP, which uses UDP >port 520. ( BTW, I have also read in a reputable source that UDP is >application layer because it is not reliable, and therefore cannot be >transport layer, and there is no place else it really fits ) > >I recognize that Cisco just LOVES the OSI model in the lower level >certifications, but the fact is that in terms of how things work it is >crap, >and tends to cause more confusion and add no value. > >Every vendor of content switches is calling them layer 4-7 switches. what >kind of crap is that? >I dare anyone to justify switching as a layer 5 or a layer 6 activity. Yet >there it is. Also, to judge from what content switches do, the marketers >are >saying the OSI layer 7 is user application, not a service application, >something Howard takes great pain to differentiate in his writings on the >subject, again IIRC. > >TCP/IP is NOT OSI compliant, never has been, never will be. OSI is a >reference model, and not necessarily related to anything in real life. > >End of rant. > >Chuck > > > >-----Original Message----- >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of >Jose Luis De Abreu >Sent: Thursday, December 13, 2001 12:25 PM >To: [EMAIL PROTECTED] >Subject: Routing protocols [7:29139] > > >Just an open question ? > >We read, learn and teach Routing protocols are at the >NETWORK layer of the famous OSI model... > >But they have PROTOCOLS NUMBERS - TRANSPORT LAYER(such >as IGRP protocol 9, EIGRP protocol 88 and OSPF >protocol 89)and APPLICATION PORTS values - APPLICATION >LAYER (RIP uses port 520 and BGP4 uses port 179) >indicating they work in the upper layers and not in >the network layer, although the result is shown int >the NETWORK layer... > >So may question is... > >Do they really operate at LAYER 3 ? > >Warm regards, > >Jose Luis De Abreu > > > > > >______________________________________________________ >Send your holiday cheer with http://greetings.yahoo.ca Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=29173&t=29139 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
