Dear JINMEI
It seems to me that the following issue needs further clarification.
- Semantics about the L=0 and A=1 case
by Fred Templin, Feb 2003
I think the prefix of L=0 and A=1 may cause an undetected address duplication.
Because the currend DAD scheme uses NS/ NA exchange, which can't go over
a router, a duplicate address may be configured on a separate link, when a router
advertises a prefix with L = 0 and A = 1.
Here is an example. Assume a router has two interface which are attached to two
separate links. It assigns the same prefix A:: to them and advertises the Router
Advertisement messages with the prefix A:: with L bit (on-link flag) off and A bit
(autonomous address-configuration flag) on.
+---------+
A:: | | A::
---------+-----+ Router +-----+---------
| | | |
A::1 | +----------+ | A::1
| |
+---+---+ +---+---+
| Host1 | | Host2 |
+-------+ +-------+
Assume there is a host with address A::1 in the first link. Then another host arrives
at the second link and forms an address with stateless address autoconfiguration.
The second host happens to have 1 as its interface id and picks A::1 as its address.
Then, even though the second host performs DAD, it can not detect the duplicate
address on the first link.
The current DAD scheme can guarantee the uniqueness of an address only inside
a link. It uses the Neighbor Solicitation/Neighbor Advertisement message exchange
to detect duplicate address. Because the messages can't go over a router, DAD may
not detect a duplicate address in an another link.
there is some discussion on this at Sec 2.4 of
http://www.ietf.org/internet-drafts/draft-jinchoi-ipv6-cra-00.txt
Best regards
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