Re: Updated UDP tunneling specification: draft-fairhurst-6man-tsvwg-udptt-01

[Gorry Fairhurst <gorry at erg.abdn.ac.uk>]

Stig Venaas wrote:
> Gorry Fairhurst wrote:
> > Stig Venaas wrote:
> > > I think this is a good idea, just some minor comments.
> > >
> > > The draft says that the checksum will usually be constant for a UDP
> > > flow. This is nice. For some tunnels it can even be computed at
> > > configuration time (when the end-points are determined). I guess
> > > the main case where this isn't the case, is when some datagrams
> > > are fragmented but not all).
> > I think I agree. IPv6 fragmentation results in some unwanted issues.
> >
> > draft-eubanks-chimento-6man-00 notes:
> >        The tunneling protocol and implementation must not use
> >        fragmentation of the inner packets being carried.
> >
> > So, in the current version of UDPTT (-01) it says:
> >       The tunneling protocol and implementation MUST NOT be used to
> >       transport IPv4 or IPv6 packets that use network-layer
> >       fragmentation.
>
> But you are then talking about the packets being transported
> (encapsulated inside UDPTT) not being fragments, right?
>
> I believe the UDPTT checksum may depend on whether the UDPTT datagrams
> get fragmented after encapsulation.
>
> Anyway, not a big deal, and I agree that all fragmentation is evil :)
>
> Stig
>
Ah, I see. I'm not sure we can do much about this. However I think it 
doesn't change the UDPTT checksum - since this is basically the 
pseudoheader of the datagram.

> > > Regarding middleboxes. It says:
> > >
> > >    o  Middleboxes SHOULD NOT truncate IPv6 datagrams where the IP length
> > >       exceeds the Length specified in the UDP Header.
> > >
> > > I guess some middleboxes might currently also just discard them? Or
> > > maybe discarding is a kind of truncation :) I also wonder whether it
> > > would be better to say MUST? At least they cannot support UDPTT unless
> > > it is a MUST. Or at least a MUST when the length is 8.
> > OK, this may also be good advice for the next revision.
> >
> > > Stig
> >
> > Gorry