Thanks for the feedback everyone. I'll just summarize here what feedback
I've gotten so far. Still waiting or more reasons we need the
mesh-header, and feedback from others who have implemented and are using
mesh-header forwarding.
So far then we have 2 features the mesh-header allows:
- Specification of intermediate destination (e.g. a particular BbR),
but this comes at the cost of mesh-header + HC dst address for
addressing outside the lowpan. Does the current BbR actually require
this wrt the primary router?
- Fragments are not reassembled at intermediate hops.
Are there some down-sides to doing IPv6 routing inside the lowpan?
- Fragments must be "reassembled" at each router in the lowpan. Not
necessarily a bad thing, could allow for hop-by-hop recovery.
- We may have IPv6 ND issues if each node in the lowpan is an IPv6
router. We need to differentiate between lowpan IPv6 routers (LpR?) and
BbRs. IPv6 routers inside the lowpan should not e.g. send their own RAs.
As far as I understand ISA100 could just as easily use HC to achieve the
routing options it has in mind. Geoff, Pascal, is this correct?
Pete had a good point about not prematurely depreciating something that
works and is in use. However I would still like to hear who is really
using it. I have an understanding there is actually quite equal
implementation and deployment experience for both IPv6 routing and
mesh-header forwarding inside lowpans at this time. I would say both
work fine. However we don't have a standard algorithm for mesh
forwarding (and are not going to get it), so what happens when ROLL
algorithms come into use?
For example, our forwarding algorithm could just as easily store the
src+dst+hopcount in the IPv6 header using HC as in the mesh-header as
now without penalty. In practice in limited nodes lowpan and IPv6 are
processed and implemented together, it is really a very small
implementation detail whether to look at the mesh-header or HC IPv6
header for the dst address, and then consult your routing table for the
next hop.
- Zach
--
Zach Shelby | Head of Research | +358 40 7796297
Sensinode Ltd. www.sensinode.com
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