[riot-devel] Fragmentation support in IP

Carsten Bormann cabo at tzi.org
Thu Aug 18 22:54:21 CEST 2016


Hi Adeel,

IP fragmentation is usually a bad idea*), and more so on a constrained
network.  If you need to transfer payloads beyond a kilobyte or so,
maybe CoAP (RFC 7252) with the block-wise transfer protocol (currently
being published as RFC-to-be 7959) solves your problem.

Which encryption expands a few bytes of plaintext to kilobytes of
ciphertext?  (You may be thinking about signatures; e.g., hash-based
signatures can be 3-6 KiB or even more.  These might occur in firmware
updates and are covered quite well by CoAP + block-wise.)

Grüße, Carsten

*)
https://tools.ietf.org/html/draft-mathis-frag-harmful-00
http://www.hpl.hp.com/techreports/Compaq-DEC/WRL-87-3.pdf

Adeel Mohammad Malik wrote:
> Hi Thomas,
> 
> I agree that IP fragmentation is not an equivalent for data streaming.
> However it still facilitates transporting data that exceeds the MTU. The
> use case we are looking at is encryption of IoT data that may result in
> a few bytes of plaintext being converted to a few kilobytes of
> ciphertext. Had IP supported fragmentation in RIOT it would have been
> possible for us to send such data.
> 
> /Adeel
> 
> 
> -------- Original message --------
> From: "Thomas C. Schmidt" <t.schmidt at haw-hamburg.de>
> Date: 8/18/2016 18:11 (GMT+01:00)
> To: devel at riot-os.org
> Subject: Re: [riot-devel] Fragmentation support in IP
> 
> Hi Adeel,
> 
> GNRC in RIOT supports fragmentation, e.g. in the context of 6LowPAN.
> 
> However, you seem to be interested in sending UDP datagrams that exceed
> the MTU payload size. I don't think this is common use ... and I don't
> think this is clever, either. IP fragmentation is not an equivalent for
> data streaming.
> 
> Cheers,
>   Thomas
> 
> On 18.08.2016 18:04, Adeel Mohammad Malik wrote:
>> Hi all,
>>
>>
>>
>> My question is about fragmentation support in IP in RIOT. Does IP in
>> RIOT support fragmentation? The use case I am after is transferring a
>> large blob of data (let’s say 5 kilobytes) on the UDP/IP stack in RIOT.
>> Is that possible?
>>
>>
>>
>> I know that 6LoWPAN supports fragmentation but that is below the IP
>> layer. I am interested in fragmentation at the IP layer so that
>> application running over it in RIOT can send large data.
>>
>>
>>
>> Regards,
>>
>> Adeel
>>
> 
> -- 
> 
> Prof. Dr. Thomas C. Schmidt
> ° Hamburg University of Applied Sciences                   Berliner Tor 7 °
> ° Dept. Informatik, Internet Technologies Group    20099 Hamburg, Germany °
> ° http://www.haw-hamburg.de/inet                   Fon: +49-40-42875-8452 °
> ° http://www.informatik.haw-hamburg.de/~schmidt    Fax: +49-40-42875-8409 °
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