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Date:      Thu, 05 Apr 2001 13:38:54 -0400
From:      "Louis A. Mamakos" <louie@TransSys.COM>
To:        Wes Peters <wes@softweyr.com>
Cc:        Brett Glass <brett@lariat.org>, freebsd-net@FreeBSD.ORG
Subject:   Re: Transition from modem PPP to PPPoE 
Message-ID:  <200104051738.f35Hcsn53390@whizzo.transsys.com>
In-Reply-To: Your message of "Wed, 04 Apr 2001 22:12:38 MDT." <3ACBF0B6.52B99863@softweyr.com> 
References:  <4.3.2.7.2.20010330201802.00dc8f00@localhost> <4.3.2.7.2.20010401141552.0452a6c0@localhost> <3ACBF0B6.52B99863@softweyr.com> 

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> > The way the network is set up, not all of the nodes can
> > hear one another, but all can communicate with the hub. Using PPPoE
> > makes the traffic go through the hub without subnetting (which
> > would require reconfiguring many machines, some of which I do
> > not administer). Could you suggest a better solution?
> 
> Sounds like an interesting network configuration.  I don't know of a tunnel
> program like I described above, but it would be pretty simple to develop
> one using the tun device in FreeBSD.  If you don't have FreeBSD at both
> ends, PPPoE or another tunnelling application probably is your best choice.
> It would be worth searching for a solution with less overhead than PPPoE.

It's hard to imagine how PPPoE is going to add more overhead than,
e.g., 20 bytes for IP-in-IP.  This is an interesting application for
PPPoE, which I don't think was anticipated in the initial design, but
it sure seems like it would work.

A question you have to ask yourself is by what metric do you measure
"overhead?"  Is it bytes on the wire, CPU cycles in the boxes at the
ends, or administrative "costs" in operating a system.  Various
schemes each will have their own characteristics for each of these
metrics.

I've never thought that the 4 bytes of overhead per PPPoE frame was
terribly inefficient, compared to, say, IP-in-IP with another 20 byte
IP header.   But I'm certainly not arguing that a choice of technology
be made on simply the number of bytes on the wire; there are other
things to consider as well.

louie



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