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=29159&t=29139 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
