[lwip-users] Re: [lwip] IP fragmentation support questions

[Adam Dunkels]

Hi!

On Monday 20 May 2002 08.44, you wrote:
> Because the proxy will communicate with arbitrary
> Internet hosts, it must support all essential features
> of TCP. Hence IP fragmentation support is required.
>
> has anyone tested the IP fragmentation code? Does it work?
> (it seems commented out)
>
> can it handle many simultaneous streams at once?

The IP fragment reassembly code in lwIP is currently very untested. It looks 
allright, but there are probably bugs lurking in it. The code works by using 
a single buffer which holds one packet to be reassembled. Thus is cannot 
reassemble more than one packet in parallell.

This should not be a very serious limitation, however, as fragmented TCP 
packets are *very* uncommon. Fragmented UDP packets are common on LANs 
becuase of NFS sending 8k UDP chunks which are fragmented into a number of IP 
packets (on Ethernet). Since TCP usually limits the MSS to 1500 most TCP 
streams never include any fragmented packets. (Studies of packet traces from 
wide area networks have shown that > 0.1% of all packets are fragmented.)

> what other important TCP features need supporting?
> (ECN ius another I know about, but its not really
> essential)

All features needed for full interoperability should be included in 0.6. 
There are a few things missing in 0.5.3, such as urgent data and zero window 
probing but none of those lead to communication failures. 

/adam
-- 
Adam Dunkels <address@hidden>
http://www.sics.se/~adam
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