Re: PPP

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At 03:55 AM 2/28/2002, you wrote:
>In what layer is PPP in the TCP/IP suite?

I have read some of the other responses and it reinforces my belief that 
most people don't understand PPP's relationship to IP and either the 
5-layer (internet) or 7-layer (ISO) models.

PPP is really both the link and lower network layers. (The ISORMites 
discovered that layer three was really several layers in itself but found 
it difficult to say that the 7-layer model was really a 9-layer model so 
they created sublayers, i.e. layers 3A, 3B, and 3C.  Something about 
Padlipsky comes to mind here.) The best way to think of PPP is a degenerate 
network of two nodes, not a link between two devices.  If you think of it 
in this way, things like multilink and L2TP begin to make some sense.  The 
problem occurs when people forget this.

The way that I think of it is that the LCP negotiation represents 
configuration of the link layer while the NCP negotiation configuration at 
the network layer.

And I continue to kick myself for allowing negotiation of multilink as part 
of LCP instead of doing it after authentication.  I fear that this helped 
screw up L2TP too.  I admit I caved to people who were worried about how 
long it took PPP to complete negotiation, something that just isn't very 
important.


Brian Lloyd
brian@lloyd.com
+1.530.676.1113 - voice
+1.360.838.9669 - fax


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