Re: A list of issues for RFC2462 update: L=0 and A=1

["JinHyeock Choi" <athene@sait.samsung.co.kr>]

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

JinHyeockLR¿¬(®H§‚
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