Re: [lwip-devel] [bug #24493] Dropped incoming packets cause a burst of duplicate ACKs

[David Woodhouse]

On Thu, 2008-10-09 at 10:43 +0100, Kieran Mansley wrote:
> On Thu, 2008-10-09 at 09:25 +0100, David Woodhouse wrote:
> > On Thu, 2008-10-09 at 08:17 +0000, Kieran Mansley wrote:
> > > the sender doesn't know that we've buffered some of the frames after
> > > the original loss, and so sends them all again. 
> > 
> > So why don't we tell it? :)
> > 
> > Has anyone looked at implementing SACK?
> 
> It's simply a case of a trade off with code size and computation that
> doesn't fit well with the goals of lwIP.

Even as an option? Is SACK really that complicated? 

Lack of it is likely to be a show-stopper for the application I was
planning. I was working on a SOCKS server which uses lwip to communicate
across a VPN -- having made the VPN dæmon talk to a child process over a
UNIX socket, instead of using a kernel tun/tap device. I have the
simhost hooked up to the VPN and I can telnet into it over the VPN; I
was just playing with the bits which listens as a SOCKS server on the
'real' host and does DNS lookups over the VPN.

Lost packets are going to be common, and SACK would be sorely missed.

-- 
dwmw2