From: Ruaidhri Power (ruaidhri at domain netsoc.tcd.ie)
Date: Wed 05 Jun 2002 - 20:09:32 IST
On Tue, Jun 04, 2002 at 10:51:15PM +0100, Karl Jeacle wrote:
> FWIW, PPPoE encapsulation uses 8 bytes, so while an IP packet on
> ethernet would normally be up to 1500 bytes in length, when using
> PPPoE, it has a maximum size of 1492.
I came up with an issue on this when setting up our gateway machine,
though I used OpenBSD. When I would ssh in from outside, occasionally
the connection would die when there was a lot of outgoing traffic, like
when I read a man page on a maximised terminal.
It turned out that the problem was that whenever a 1500-byte packet was
generated on the local network and destined for the outside, it wouldn't
`fit' out our ADSL connection, which had an MTU of 1492. The problem
was solved by upgrading our ppp, to be able to use the `mssfixup'
option:
[tcp]mssfixup
Default: Enabled. This option tells ppp to adjust TCP SYN pack-
ets so that the maximum receive segment size is not greater than
the amount allowed by the interface MTU.
Does Linux PPPoE take care of that automatically? It might be something
to have a look into, in case it bites you later.
-- Ruaidhri
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