=?EUC-KR?Q?=AE=A1?= Re :Re: [DNA-BOF] DAD Optimization ProblemStatement CHOIJINHYEOCK i_Networking Lab Samsung AdvancedInstitute of TechnologyResearcher

[CHOIJINHYEOCK <jinchoe@samsung.com>]

Hi Greg

> If we were talking about networks where all addresses
> aren't on-link (which I think we were trying to avoid),
> then the router should be ND-proxying.

Even if all addresses aren't on-link, the router doesn't have to be 
ND-proxying necessarily. In the example below, what give rise to 
trouble is a prefix with L bit off and A bit on. If both bits are off, 
I see no problem. 

> DAD has to work, or this type of link will never be
> deployed. Therefore i think that it's the problem
> of the multi-link or ND proxy people when they develop
> standards, rather than our problem.

>> If people are doing DIID (checking only the link-local
>> address) on systems where they are told by an RA that
>> the on-link bit is not set, then that's _their_
>> problem, as they're not actually doing DAD on their
>> non-link-local address.

Correct me if wrong, but I am afraid that there is no way 
people can do DAD on their non-link-local address other than 
the above (DIID like). What other mechanism can they rely on?
 
>> This is tricky and gave me some trouble when I thought over movement 
>> detection. 
>> 
>> My guess is that it enables the node to check whether it has a valid address. 
>> In other words, if its IP address belongs to the advertised prefix (whether 
>> L=0 or L=1), the node can expect that the internet routing system will deliver 
>> packets destined to that address to itself. 

What I described above has nothing to do with DAD, I just try to elaborate the 
usage of the prefix with L=0. 

And if we put A bit off, we can do DAD in stateful manner (maybe in DHCP 
server). 

>> As in RFC 2461, a prefix might be used for address configuration with 
>> some of the addresses belonging to the prefix being on-link and others 
>> being off-link. 
>> 
>> But I am afraid this kind of usage may result in duplicate addresses 
>> like below. 
>
> This is not the case, if the route has to deliver packets
> to these hosts from off-link.  In that case, it MUST
> know where to send them, and must keep some state, or
> relay ND messages between links.

What I trying to say is that if we put L bit off and A bit on, there may 
be a problem, two identical global addresses, as described in an example. 

> Please remember that we've been cautioned about
> tackling multi-links in DNA:
> 
> http://webcamserver.eng.monash.edu.au/~warchive/dna/2003-06/msg00063.html

What concerned me is not multi-link but the prefix with L bit off. I will 
be glad if we don't have to worry about the prefix with L bit off. It will 
ease our work considerably. But can we? 

Currently ND assumes transitivity. In other words, any two nodes 
attached on the same link (for example, ethernet) can communicate 
each other directly without going through a router. This may not be 
the case in wireless environments, where some address, we 
can communicate directly but the other addresses, we have to go 
through a default router. In this case, every prefix should be 
advertised with L bit off.  

> I'd really prefer to leave all this (section 3.3, and
> link-local scope of DAD)  out of the document,
> since it is not a DAD optimization issue.

Though, I think this is a problem, I can't be sure this is a
DNA problem. If folks think not, I will not cling to it with
tooth and nail :-).