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RE: [manet] Three issues with PacketBB

> So two IPv4 addresses differing at the seventh most significant bit
will 
> have to be encoded without a common head part - right?

Right.

> In this case, the spec doesn't seem to say whether a head-length is 
> absent or present  but equal to 0:
>>    <head-length>  if present is an 8 bit field, which contains the
total
>>       length (in octets) of the head of all of the addresses.

That "if present" is a pretty good hint that it doesn't have to
be present. But more importantly you missed

      bit 0 (nohead):  if cleared ('0'), then <head-length> is included
         in <address-block>, and <head> may be included in <address-
         block>.  If set ('1'), then <head-length> and <head> are not
         included in <address-block>.

As for including a <head-length> equal to zero, it's legal.
Not efficient, but legal.

> YEs, but this doesn't show the necessity of the third 'mid' part.
There 
> are only two parts: head and tail ('head' is first 64bits and 'tail'
is 
> the Interface ID or EUI-64).

No, what I'm saying is that a node may use (using upper case letters
for 64 bits and a / to join them) A/Z and B/Z as two addresses of
the same interface, where Z is its EUI-64. Of course A and B may
also have some head bits in common, or may not.

> And 'mid'?

mid is the uncompressed bit. Always is. Sometimes you have a common
head. Sometimes you have a common tail. Sometimes you have both.
Sometimes you have neither. mid is the bit in the middle that is
different. It can have zero length but that will be (I expect)
uncommon.

> YEs, I agree, but there is much more here than just IPv6 address 
> architecture once you say PacketBB packets are transported in UDP over

> IPv6...

But invisibly to IPv6. packetbb is just carrying the addresses.
It's up to a protocol that does know something about addresses
- maybe DYMO, maybe an autoconf mechanism that uses packetbb
to interpret those addresses. packetbb is NOT a protocol.

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