[RP-PPPoE] Enabling MTU/MRU 1500 (as per RFC 4638)

[Robert Laverick]

I've managed to get it to compile by dropping the use of the
lcp_wantoptions[] and just delcare "allowmru" and "wantmru" as
externs, and then hardcode the want MRU to 1500.  this does seem to
connect, and I am connected, and my ISP reports that the handshake has
worked and my connection MRU is 1500.

obviously that's the wrong way to do it, as I should be getting the
wantmru value from the command line config setting, which is I suspect
the point of the lcp.c stuff that I've not included, but on the other
hand I've got a working 1500 MTU/MRU pppoe internet connection :-)

The code in question (by Simon Arlott) is only in their git repo, it's
not in the release version of pppd, and I think the person who pointed
me at the patch might even have been it's author.

This code only bumps the max MRU from 1492 to 1500, tho the RFC
doesn't actually put such limits on the size, only saying that it's a
mechanism for allowing larger than 1500 (outer Ethernet) channel
sizes, so while in my case I'm only interested in increasing to 1500
(1508 outer) which this patch provides by nudging up the buffers to
cover the smaller difference.  I can't see an RFC with an actual size
limit on jumbo frames, FWIW my LAN cards seem to do 7200 MTU, tho what
my ISP supports on the other end is anyones guess :-)

If you don't have a setup you can test this on, I'm more than happy to
help test any versions you come up with.

Rob

On 2 May 2011 02:55, David F. Skoll <dfs at roaringpenguin.com> wrote:
> On Mon, 2 May 2011 01:51:41 +0100
> Robert Laverick <robert at scabserver.com> wrote:
>
>> My ISP supports an MTU of greater than 1492 (1500) pppoe using baby
>> jumbo frames as pre RFC 4638.
>
> I'll take a look at that RFC and your patch; thanks.
>
> I really, really, *really* wish the pppd developers would pass stuff like
> this upstream to me.  Feel free to complain to them that they don't. :(
>
> Regards,
>
> David.
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