[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [lwip-users] MSS Configuration Difficulty

From: Kieran Mansley
Subject: Re: [lwip-users] MSS Configuration Difficulty
Date: Mon, 14 Feb 2011 14:39:03 +0000

On Mon, 2011-02-14 at 07:30 -0700, address@hidden wrote:
> We have been using lwip version 1.2

I would strongly suggest upgrading.  1.2 is years out of date and even
more unsupported than the current version (we're about to release

> At this point, we are not using any TCP options, so we believe 1460
> would suffice. I would definitely appreciate any feedback on that
> assertion. 

1460 sounds good to me.

> In our case the p->tot_len is 3016, and the sum of
> the p->len is 1516.  Since the loop is traversing the packet chain
> until the tot_len is zero, this walks off the end of the chain.
> What I'm unsure of is whether the IP fragmentation code can tolerate
> this misconfiguration of the MTU, or whether there is likely an error
> in the fragmentation code, or perhaps in one of our drivers. 

I'm not sure which is to blame either, but with mismatch between
p->tot_len and sum(p->len) is definitely a problem.  As I said before,
I'd strongly suggest upgrading to 1.4.0 as there's a chance this was an
lwIP bug that was already fixed (although it doesn't sounds familiar to

> Any thoughts on this are greatly appreciated. Additionally, since we
> are executing in a real-time multi-threaded environment our
> investigation is focusing on timing and race condition scenarios. Feel
> free to chime in with observations and experience in those areas as
> well.   

You have to be particularly careful with lwIP in these environments and
ensure that only one thread is active in the lwIP core at once.  A
common way that failure to do this manifests itself is for lists of PCBs
or pbufs to become corrupted.  This therefore might be the cause of your


reply via email to

[Prev in Thread] Current Thread [Next in Thread]