Re: [lwip-devel] IP fragmentation

[Jonathan Larmour]

Goldschmidt Simon wrote:
> > I'm looking at the code to do the IP reassembly, and notice that it
>
> appears
>
> > that it is only able to handle a single fragmented payload at a time.
>
> Is
>
> > this really true, or am I seeing things again?  If so, the
>
> implementation
>
> > is somewhat problematic in that if one of the fragments of an IP
>
> datagram is
>
> > lost, then the ip_reass_tmr has to expire before the stack can handle a
> > fragment belonging to a new IP datagram.  By default, this timer is set
>
> to
>
> > expire every seconds.
>
>
> As far as I can see, you're right. What also disturbs me is that,
> because
> there is only one reassembly-buffer, you can only receive fragmented
> IP-packets
> from one host at a time. That's because I didn't enable IP_REASSEMBLY...
> Or am I wrong and this would never happen??

This is correct and intentional - more frags to reassemble means more 
memory, it's as simple as that. You should try and avoid getting 
fragmented packets in the first place!

Of course if lwIP could implement path MTU discovery, it could keep up its 
side of the bargain.

Jifl
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