Hi René! On Mon, Jan 11, 2016 at 05:14:31PM +0100, René Herthel wrote: > i would like to implement the support (TODO [1]) for elided checksum of > compressed udp pakets on the gnrc.
Thanks for offering your help regarding this topic.
> So therefore i have some questions:
> Is someone already working on it?Is there any reason why this is not
> implemented before?Are there some things i should definitely know? ( like
> other work/PR's which have to be done first, or something else..)
I think there exist some reasons why this hasn't been implemented yet. While
decompressing packets with elided UDP checksum shouldn't be problematic,
for the compression itself some considerations has to be taken:
1.) RFC 6282, Section 4.3.2 [2] specifies that the upper layer must authorize
the header compression module to elide the checksum. This is only possible
if tunneling (like IPsec Encapsulating Security Payload tunnel mode) or
another message integrity check (such as IPsec Authentication Header) is
present in the UDP payload. Since IPsec has not yet been implemented for
RIOT and to the best of my knowledge also no other tunneling or additional
integrity checking mechanism for UDP payloads exists in GNRC, there is
currently no immediate use case for UDP checksum elision. Also note that
this features is optional.
2.) Since 6LoWPAN and IPHC/NHC operates asynchronously to any upper layer, it
is not trivial to determine for which packets the checksum may be elided.
A node may communicate over UDP to several services or hosts concurrently,
where one connection may use something like IPsec and authorize the NHC
module to elide the checksum, while for another connection this should not
be allowed. I think with the current netapi calls (send and setting of
netopts) this is not easy to implement. Maybe other GNRC knowledgeable
persons such as Martine, Hauke, Cenk, Peter or Johann may have an idea.
> [1]
> https://github.com/RIOT-OS/RIOT/blob/master/sys/net/gnrc/network_layer/sixlowpan/iphc/gnrc_sixlowpan_iphc.c#L506
>
Cheers,
Oleg
[2] https://tools.ietf.org/html/rfc6282#section-4.3.2
--
/*
* For moronic filesystems that do not allow holes in file.
* We may have to extend the file.
*/
linux-2.4.0-test2/fs/buffer.c
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