Re: [lwip-users] ppp-new IP forwarding only works one direction (Ethernet to PPP)

[Sylvain Rochet]

Hello Simon,

On Thu, Apr 10, 2014 at 08:12:00PM +0200, Simon Goldschmidt wrote:
> Sylvain Rochet wrote:
> > Oh dear, now I see what is happening.
> > 
> > PPP header is smaller than Ethernet header
> > [..]
> > This is actually a lwIP design issue, the only way we can fix that is by
> > adding a configuration option so pbuf from PPP are allocated with enough
> > extra space so a Ethernet header will fit in place of a PPP header.
> 
> The lwIP way to solve this is to defin PBUF_LINK_HLEN to be big enough 
> for both sides. We do waste some bytes that way, but it should work.
> 
> However, I just saw that PPP (new?) seems to allocate many pbufs as 
> PBUF_RAW, which kind of breaks the link-header size calculation and 
> thus might make my suggestion not work...
> 
> Anyway, we might want to fix this in a generic way...

PPPoE use PBUF_LINK, PPPoL2TP use PBUF_TRANSPORT, PPPoS use PBUF_RAW, it 
all makes sense at first sight and IP forwarding should work for PPPoE 
and PPPoL2TP. Maybe we should allocate a PBUF_LINK for PPPoS as well.

Sylvain

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