[dtn] BPbis rules for future extension blocks

[Magnus Westerlund <[e-mail]>]

Hi WG,

So in the discussion of BPv7 Extension in todays meeting some people did draw
some parallels to IPv6 Extension headers. Ben Kaduk reminded me that there is
one important aspect of that discussion that can hint at an issue. If you are
following 6man and/or Spring WG you would know about the big discussion related
to addition and removal of some IPv6 extension headers by anything other than
the endpoints that IPv6 Segment routing proposal has caused.

So the existing Extension headers are all being changed interally and at least
"received from" will be added by a forwarder which isn't the originating
endpoint.  So the question to the WG and especially the authors. Is it really
clear that Extension bundle blocks MAY be added by any node? Which nodes MAY
remove a Extension bundle block? What controls if a Extension Bundle Block can
be removed by an intermediate node. I do note taht the Block Processing Control
Flags do not have a flag for "MUST NOT be removed, even if not understood". 

I would encourage the WG to think if there need to be any clarification of this
now. If we are missing a control flag I think it is easier to add it now. Also
to clarify what the general rules are for Extension Blocks so that this
discussion don't show up a bit down the line here. 

Cheers

Magnus