Colin O'Flynn a écrit :
Hello,
Excuse me, sorry, but are the other non-16bit addresses (48bit)
ever assigned by DHCP?
There's at least two options I know of for this:
#1 Add another 6lowpan-nd specific extension to DHCPv6 to add a
simple link-layer address option
Hmm... makes some sense, what would it look like? (rfc4944 defines such
an option for ND).
What would it be used for and how?
#2 Nodes could assign their own short addresses. Nodes power on and
autoconfigure a IPv6 address based on the 64-bit MAC address.
You mean the "EUI-64 Identifier"? (it's not an address, it's an
identifier). Is there such a thing as a 64bit MAC address?
With this they then do the DHCP dance, and get another address.
Sounds as forming an IPv6 link-local address in order to do DHCP dance
prior to obtain a global IPv6 address. (yes, in IPv4 one could say that
the node uses its MAC address while doing the DHCP initial dance and the
unspecified IPv4 address 0.0.0.0, but in IPv6 the unspecified addresses
(search " :: " in rfc3315) are not used DHCPv6 in the initial DHCPv6
dance, but the link-local addresses are).
Forming an IPv6 link-local address based on the 16bit short MAC address
- ok, using on RFC4944. And then do DAD on this IPv6 link-local
address, because the EUI-64 identifier based on the 16bit short MAC
address is not guaranteed global, has that g bit unset.
Nodes check if this address can be used to assign their own short
address.
Yes, usually they do DAD to make sure their IPv6 link-local address is
unique within that link.
But don't rely on the IP address uniqueness to conclude that the MAC
address corresponding to that IP address is unique.
Aka: the IPv6 address it assigns matches the prefix, the PAN-ID, etc.
Sorry can't follow this. Which prefix? Which PAN-ID?
Thus nodes 'figure out' if a certain short address will make their
IPv6 address compressible.
Do IP nodes care whether their MAC address (the short MAC address
included) is unique? I don't think so. I think IP nodes care only
whether their IP address is unique.
Also, it is completely unclear to me what kind of layer does 6LoWPAN
deal with - is it IP? Is it MAC?
Alex
Regards,
-Colin
-----Original Message----- From: [email protected]
[mailto:[email protected]] On Behalf Of Alexandru Petrescu
Sent: December 16, 2009 9:14 PM To: [email protected] Cc:
[email protected] Subject: Re: [6lowpan] Whiteboards
Daniel Gavelle a écrit :
I agree with the recent proposal to remove the mandatory
requirement for a whiteboard and duplicate address detection.
However, 16 bit 802.15.4 addresses are a very useful optimisation.
Assigning these in a standard way is important in the absence of a
whiteboard. One option may be to use DHCPv6. However, the DHCPv6
packet sizes are quite large and so some sort of DHCPv6 message
compression would be useful. Extended LowPANs would also be useful
in some applications.
If the whiteboard and DAD are removed, I would like the issues of
16 bit address assignment and extended LowPANs
Excuse me, sorry, but are the other non-16bit addresses (48bit) ever
assigned by DHCP?
I doubt IETF could spec a means to assign MAC addresses...
Thanks,
Alex
to still be addressed by an RFC
within the IETF 6LowPAN group, rather than having several different
non interoperable implementations.
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