Hello Michel Your proposal is feasible; the datagram space is probably overly large anyway. But it seems to be tailored around your exact problem as opposed to generic. There are alternates like use a different unit, e.g., 4 bytes words as the existing text suggests. Maybe we could make the unit dependent on the MTU, like 1 byte under 128, 2 bytes till 256, and 4 bytes above that? It seems that you are not concerned with the overall IP packet size, which is constrained to 2K by the fragment_offset. Maybe we should also look at that?
All the best Pascal From: 6lo <[email protected]> On Behalf Of Michel Veillette Sent: mardi 8 janvier 2019 18:38 To: [email protected] Subject: [6lo] draft-ietf-6lo-fragment-recovery maximum fragment size too small Hi authors of "draft-ietf-6lo-fragment-recovery" I'm currently working on a fragment forwarding implementation based on "draft-ietf-6lo-fragment-recovery". In some cases, relatively large fragments need to be supported (i.e. minimum MTU transferred using 3 fragments). However, the current format of the RFRAG Dispatch type limits fragment size to only 128 bytes. Is it possible to modify the RFRAG Dispatch type (https://tools.ietf.org/html/draft-ietf-6lo-fragment-recovery-00#section-5.1) and corresponding RFRAG Acknowledgment Dispatch type (https://tools.ietf.org/html/draft-ietf-6lo-fragment-recovery-00#section-5.2) to allow larger fragments? For example: 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1 1 1 0 1 0 0| fragment_size |X|E| datagram_tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |sequence | fragment_offset | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1 1 1 0 1 0 1 Y| R | datagram_tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RFRAG Acknowledgment Bitmap (32 bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ R = reserved Regards, Michel Veillette
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