Re: [B.A.T.M.A.N.] BATMAN-Adv and MTU handling

Linus Lüssing
2009-11-23T14:21:51Z

> > Hmm, yes, true, IPv6 does not support fragmentation at all...
>
> It does, but it's done end-to-end, not at intermediate routers. See
> Section 5 of RFC 2460.
Ah, ok, yes, you're right, forgot about the fragmentation header
in IPv6 :).

If BATMAN were just doing transparent link fragmentation towards
its neighbours as a "fall-back" mechanism despite header
compression, would it be better to also do something like
"aggregation"? So for example if we were receiving a packet of
1500 bytes, which does not fit through a bat0 interface with an MTU
of 1476, we could wait for a maximum of maybe 5ms for another
packet and send a packet fragment of (1476 - (fragmentation
information overhead)). A second packet fragment would be send with
the rest of the first and the beginning of the second packet.
Wouldn't that cause a lot less loss of throughput compared to
splitting it in two packets of equal size as done in fragmentation
in IPv4 (in fact, only the additonal fragmentation header
overhead of a couple of bytes, especially in lossy environments
like wifi, right?). Any concerns about such an approach?

Cheers, Linus