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Re: Bezeq ADSL setup




On Mon, 11 Jun 2001, Miki Shapiro wrote:

> Now to fragmentation problems: 
> 
> Fragmentation is done when data passes between layers, and, providing that
> I trust my ISP's tunnel enterance and my linux router's tunnel exit (or
> vice versa), fragmentation somewhere in the tunnel infrastructure is
> botched up.
> 
> Now, for my two Issues:
> 
> I
> ---
> If I understood this correctly from Mulix, when a too-large packet
> containing ppp-encapsulated stuff comes to the ADSL modem on
> ethernet interface and wants to go on the DSL interface, the frarmentation
> mechanism of the modem (I'm talking about my ATUR3) is broken.
> Workaround: don't send packets larger than so-and-so from your linux box
> to your ADSL modem.
> The bottlenecking is done by the ppp interface (limited to MTU 1452) and
> once we do that, We're completely sure that the packets that reach the
> ADSL modem over the ethernet interface will be no larger than
> (what the ppp driver constructed plus the 48 bytes it added) - 1500 bytes
> and their ppp core will be no larger than 1452.
> And if they're smaller than 1500, the modem doesn't need to frag them
> before sending over the DSL. Problem Solved.
> 
> Now can someonce PLEASE explain to me why we need a SECOND bottleneck by
> limiting the MTU Win9x-client-to-linux-over-ethernet traffic, as this
> traffic is bekol-mikre encapsulated in the ppp shell, and isn't seen by the ADSL
> modem as IP traffic at all?
> Why wouldn't an ethernet with 64K IP packets work? If I understand
> correctly, it would.

It is my complete guess that the Linux 'NAT' code forwards packets and
only rewrites the source IP/port address on outgoing packets and does not
modify the packet in any other way (like fragmenting it).  Someone correct
me if I am wrong ;)

-Cedar



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