Subject: Re: PPPoE vs ETHERMTU
To: Brian Somers <brian@Awfulhak.org>
From: Martin Husemann <firstname.lastname@example.org>
Date: 07/03/2001 20:21:06
> I believe the 1490 MTU is used when (MPPE) encryption has been
> negotiated. MPPE encrypts each packet to the same size as the
> unencrypted packet, but also encrypts the protocol id, increasing the
> payload by two bytes.
I do not pretend to have read the MPPE RFC yet, so probably just am
misunderstanding what you said. In PPPoE the 6 byte PPPoE header is always
followed by the PPP protocol ID (two bytes), followed by payload data,
that's why the MTU is 1500-6-2 = 1492.
Besides, MPPP over PPPoE sounds - strange.