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[OT] TCP/IP and OSI (Was: Re: MAC-based ssh)

On Fri, 02 May 2003 at 06:20:58PM +0200, Peter Ondraska wrote:
> Doesn't TCP/IP have only at most 4 layers?

In the OSI model there are 7 Layers.  TCP/IP takes up only two of them
(3 & 4).

Layer 1 - Physical - Cat5, Fiber, etc.
Layer 2 - Datalink - Ethernet, FDDI, etc.
Layer 3 - Network - IP, IPX, etc.
Layer 4 - Transport - TCP, UDP, XPX, ICMP, IGMP, (the list goes on and
Layer 5 - Session - HTTP, SMTP, POP3, SSH, NNTP, etc.
Layer 6 - Presentation - GIF, HTML, etc.
Layer 7 - Application - Layer for communicating with the user.

So, to answer your question, yes TCP only acts at layer 4, but when one
looks at networking as a whole it goes up much farther than layer 4.
Layer 4 and down is usually the concern of the O/S.

Phillip Hofmeister
Network Administrator/Systems Engineer
IP3 Inc.

wget -O - http://www.zionlth.org/~plhofmei/key.txt | gpg --import
Excuse #71: Someone is standing on the Ethernet cable causing a kink in the cable 

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