Subject: Re: Allowing large PPPoE frames
To: Quentin Garnier <netbsd@quatriemek.com>
From: Martin Husemann <martin@duskware.de>
List: tech-net
Date: 08/03/2003 13:51:38
On Sat, Aug 02, 2003 at 11:27:55PM +0200, Quentin Garnier wrote:
> I've repeatedly ask for that change. The only answer I got was
> 'it's a flaw in the design of PPPoE'.
Well, the PPPoE standard (RFC 2516) is pretty explicit in this point.
Section 7 (LCP Considerations) says:
The Maximum-Receive-Unit (MRU) option MUST NOT be negotiated to a
larger size than 1492. Since Ethernet has a maximum payload size of
1500 octets, the PPPoE header is 6 octets and the PPP Protocol ID is
2 octets, the PPP MTU MUST NOT be greater than 1492.
So it's a flaw in their PPPoE implementation to actually allow this large
frames, and it's a configuration flaw at their router to not return need-frag
ICMPs.
I have no problem for us accepting such broken input when a special option
is present, as long as this option is pretty clear documented to be
depreciated and in violation of relevant standards.
I know how hard it is to find even semi-competent ISPs, it's a big problem
here in germany too.
Martin