Re: SOLVED: kernel-mode PPPoE does not seem able to work with MPPE.

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On 06/11/17 18:31, James Carlson wrote:
On 11/06/17 09:59, David Fernandez wrote:
Yes, the code could be deleted, I just wanted somebody to check and say
that there is no point in yet putting a warning in the log for this...
RFC3078 7.2 says that the receiver changes its key on receiving a "flag"
packet (where (count&0xff) == 0xff).  It says nothing about the
transmitter setting the FLUSHED flag in this case.  That flag is used
*only* when a sequence error is detected.

So I think the original code was wrong (it should not have insisted on
the flag being set), and the new code without the message and without
the error handling is correct.

It _might_ be a good idea to check and at least comment the sending
code.  It should not be setting the FLUSHED flag merely because it is
sending a flag packet ... but, for compatibility with broken Linux MPPE
implementations already deployed, it might have to continue doing that.

It's a shame documents like this don't go through WG review with
multiple independent implementations.  This is the sort of spec
misinterpretation that a good open review is designed to catch.

Hi James,

I think you are right, the flushed bit is only used for sequence errors in stateful mode, as that is the only way to change keys in a deterministic manner.

I'm runing now into the problem of packet loss, and I guess I'll have to modify the implementation in order to use the flushed bit instead of a reset-ack packet to decide if we have to send another reset-req after a timeout...

I think this will become a formal patch, so let me know what ettiquete bits are required and I'll prepare it for review and submission to whomever can approve and commit.


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