NFS is not a session-layer protocol. Cisco said it was in some early courseware and the mistake has lived on. The mistake is still in some CCNA and Cisco Networking Academy materials, I think, but it's wrong.
NFS is clearly an application-layer protocol. It uses XDR at the presentation layer. It runs above RPC which is a session-layer protocol. RPC runs above UDP, which runs above IP. Here was a perfect chance to show an actual 7-layer protocol stack and Cisco blew it! ;-) NetBIOS is a session-layer protocol, as I said in the message. Did you read it? SQL does application-layer stuff, like reading from databases. In an Oracle environment, it uses the Transparent Network Substrate (TNS) which has session-layer-like behavior. TNS can run above a variety of protocol stacks, including TCP/IP, IPX, etc. Cisco texts ignore TNS. I think they call SQL a session-layer protocol. Priscilla At 06:15 PM 12/7/01, anil wrote: > >The session layer is an elusive beast that is not implemented much >Wait a sec, I thought SQL, NFS and netbios were session layer protocols? >Someone please correct me. >-Anil > > >-----Original Message----- >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of >Priscilla Oppenheimer >Sent: Friday, December 07, 2001 9:55 PM >To: [EMAIL PROTECTED] >Subject: Re: Does session layer protocol use IP address ? [7:28378] > > >At 02:59 AM 12/7/01, mlh wrote: > >Hi, there, > > > >I read Todd Lammle's CCNA2.0 study guide and found this sentence: "Remember > >that none of the upper > >layers know anything about networking or network addresses." I am wondering > >if the session layer doesn't > >use network address, how can it establish a dialogue with other session > >layer in other host? > >I would probably disagree with Todd's statement, although it's taken out of >context and you haven't given us enough information to say that the >statement is definitely "wrong." > >However, try to picture the numerous OSI pictures you have seen. Most of >them show horizontal lines between a layer on one host talking to the same >layer on another host. So the session layer talks to the session layer on >the other host. That's probably what Todd was getting at. > >However, the pictures also show vertical lines. A layer calls on a layer >below to provide services. Each layer offers services to layers above it. > >The session layer is an elusive beast that is not implemented much. But one >example might help. NetBIOS is a session layer. On a Windows client, when >you access a Server Message Block (SMB) server, NetBIOS has the job of >setting up a session with the server. Before it can do that, however, it >must find the address of the server. If it's a modern Windows network, then >SMB and NetBIOS are probably running above TCP/IP and UDP/IP. So NetBIOS >sends a DNS or WINS query to find the IP address of the named server. It >then sets up a NetBIOS session with the server. Actually, first, the client >sets up a TCP connection. TCP has port numbers. The client sends to the >well-known TCP port for NetBIOS session (139) and use an ephemeral port on >its side. These port numbers could be considered "addresses" at the >transport layer. > >Anyway, back to the question. The statement is at best over-simplified. I >recommend you get yourself a sniffer and watch what really happens between >layers. (Ethereal is free by the way.) > >Priscilla > > > > >Thank you for your time. > > > >mlh >________________________ > >Priscilla Oppenheimer >http://www.priscilla.com ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=28501&t=28378 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
