RE: [manet] Three issues with PacketBB

["Dearlove, Christopher \(UK\)" <Chris.Dearlove at baesystems.com>]

I'm replying to this one, but I may cut it off then, as
time presses on other things.

> I think we don't understand each other.  I don't see how is it
possible
> to disambiguate two addresses represented as head-tail if we don't
> precisely encode the headlength.  Receiver simply can't decode
correctly 
> a field saying 3octets when sender meant 26bits.

It's really very simple. Take your example of 1.1.1.1 and 1.2.2.2.
This actually has 30 common bits. But we work in common octets
and it has 3. So we send (noting that the different pieces are
mids, not a common tail) what reports that

Head octets = 1
Tail octets = 0
(and hence mid octets = 3, as addres length = 4)
Head octet 0x01
First set of mid octets  0x01 0x01 0x01
Second set of mid octets 0x02 0x02 0x02

And it's all there.

> This means I can't encode head-tail two addresses whose most
significant 
> bits differ at a boundary different than octet - right?

Wrong. See above.

> In the example given by DYMO document the encoding is not as you say. 
> The address semantics is 1bit (you seem to say it's three).  I am not 
> sure whether this is a remark for PacketBB authors to simplify
PacketBB 
> or to DYMO authors to use it correctly.  But certainly it's an 
> incoherence between PacketBB and DYMO.

I can't remark on this aspect of DYMO, I haven't looked at it recently.
Obviously if I'd noticed an issue I'd have let the DYMO authors know,
so either it's not there, is there and I missed it, or has been
introduced since I last looked at DYMO. No idea which.

> Also please allow me to question the necessity of the 'mid' part of an
> address.

Two main reasons

- IPv6. A node may (I understand) use a common EUI-64 identifier for
  more than one interface, but with different prefixes. This would
  correspond to have a tail length of (at least) 8 octets.

- Network addresses. If I want to send e.g. 10.0.0.0/16 and 10.1.0.0/16
  then I have a common head (1 octet, 10) and a common tail (2 octets,
  0 and 0 - I can use the zerotail bit to avoid sending these).

> I would find strange PacketBB to carry IPv6 addresses and not refer to

> rfc2460.

We're only dealing with addresses, so we just need to refer to
IPv6 address architecture. And that's RFC 4291 (recently
obsoleted RFC 3513 which we do refer to.

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