On 2/5/13 6:36 AM, Brian E Carpenter wrote:
On 05/02/2013 14:11, Rémi Després wrote:
Le 2013-02-05 à 15:01, [email protected] a écrit :
With these specifications, it is impossible on a SLAAC link that two hosts that
have universal-scope addresses (necessarily different if they communicate at
the MAC layer), would have conflicting IIDs at the IP layer if they derive them
from MAC addresses.
Impossible if the MAC addresses are indeed unique. That is correct for
*almost* all cases. But not 100%.
They are different 100% of cases at the IP layer if they are different at the
MAC layer (which is needed for communication at this layer).
OK?
Not if the same MAC address appears on two different subnets in the same
site. This would work from a conventional IPv6 point of view, but it would
immediately demonstrate that the u bit does not mathematically guarantee
uniqueness.
that describes vlans on most ethernet switches...
e.g.
Vlan1729 is up, line protocol is up (connected)
Hardware is Vlan, address is 001c.7310.8864 (bia 001c.7310.8864)
MTU 1500 bytes
Up 217 days, 16 hours, 52 minutes, 58 seconds
Vlan1730 is up, line protocol is up (connected)
Hardware is Vlan, address is 001c.7310.8864 (bia 001c.7310.8864)
MTU 1500 bytes
Up 217 days, 16 hours, 52 minutes, 58 seconds
Vlan1731 is up, line protocol is up (connected)
Hardware is Vlan, address is 001c.7310.8864 (bia 001c.7310.8864)
MTU 1500 bytes
Up 217 days, 16 hours, 52 minutes, 58 seconds
Vlan1732 is up, line protocol is up (connected)
Hardware is Vlan, address is 001c.7310.8864 (bia 001c.7310.8864)
MTU 1500 bytes
Up 217 days, 16 hours, 52 minutes, 58 seconds
Vlan1792 is up, line protocol is up (connected)
Hardware is Vlan, address is 001c.7310.8864 (bia 001c.7310.8864)
MTU 1500 bytes
Up 217 days, 16 hours, 52 minutes, 58 seconds
Vlan1793 is up, line protocol is up (connected)
Hardware is Vlan, address is 001c.7310.8864 (bia 001c.7310.8864)
MTU 1500 bytes
Up 217 days, 16 hours, 52 minutes, 58 seconds
Vlan4094 is up, line protocol is up (connected)
Hardware is Vlan, address is 001c.7310.8864 (bia 001c.7310.8864)
MTU 1500 bytes
Up 336 days, 15 hours, 53 minutes, 49 seconds
There has been discussion recently in MIF of scenarios where the same
IID would appear intentionally on different interfaces of the same device.
It is not the process of generating IIDs that is a problem - that is
well defined. It is assuming after they have been generated that the
u/g bits have meaning that is problematic. (Which is also why the
solution of a reserved range makes sense for 4rd.)
Brian
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