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Home > Archive > CCNA > October 2000 > Netbios - Layer 5?
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Netbios - Layer 5?
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| Hi,
Why does Netbios operate in the session layer? Thank you.
Ed.
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| Hi Ed,
A lot of people, like you, think that NetBIOS is a transport protocol or that NetBIOS is NetBEUI or something like it. NetBIOS is not a protocol or protocol stack. What it is, is an INTERFACE that software can use that’s known as an API (application programmable interface), or actually in this case a set of 19 API’s that programmers use to connect two computers using NetBIOS names i.e.: SERVER1 This programming interface is what puts NetBIOS at the session level according to the OSI model. Some early NOS’s like Microsoft/IBM NOS used a transport protocol called NetBIOS, but this isn’t the same one. When you install TCP/IP, NWLINK or NetBUI (which are Transport protocols), each installs its own NetBIOS layer automatically. NetBIOS can run over TCP/IP, IPX/SPX, and NetBEUI separately or together. It does not directly support routing but uses one of the 3 transport protocols I used earlier. Since only TCP/IP and IPX/SPX are routable, NetBIOS info can be sent thru routers when it’s running on one or both of these protocols. NetBUEI is not routable.
Oh yeh Ed, I'm not this smart. The above is actually gleaned from a few different resources from when I was studying for my MCSE.
Hope this helped!!
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| So does that put NetBIOS in the Application layer, since it is a set of APIs? | |
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| Subnet_Zero, thank you for your response.
Perhaps I should have added the Skipters comment to my original question as Layer 7 was my thinking as to where Netbios should fall under. But with your explanation, I think I just need to read up on Netbios, itself. Any further input is welcomed. Thank you. | |
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| Skip,
Although I see where you’re coming from, API's work at various OSI layers, not just the Application layer but NetBIOS only resides in the Session layer. If you carefully consider the services that the Application layer provides, you’ll see that NetBIOS doesn’t belong there. In this case NetBIOS supported by its APIs act as an interface USED BY applications via TCP/IP and/or IPX/SPX. The interface establishes the NetBIOS names and creates a session between the 2 names.
Check out this little tid-bit from MS.
“To carry on two-way communication between computers, NetBIOS establishes a logical connection, or session, between them. Once a logical connection is established, computers can then exchange data in the form of NetBIOS requests or in the form of a Server Message Block (SMB).”
I know this kind of logic based on my 5yrs of service on the Server side. I look to this forum and the CCNP forum (since I passed the CCNA exam recently) to help me on the Cisco side.
ED: I'm hoping this will help. Also, good idea to research yourself.
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| Subnet_0
For Microsoft, that tid-bit is not bad, although it is not explained why, but you have.
Thanks,
Ed. | |
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| Thanks subnet__zero! Explanation makes sense.
Skip
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