Re: I-D ACTION:draft-hoon-mobileip-undad-00.txt

Hi Jae-Hoon and Youn-Hee,

The draft has Youn-Hee's email addres under
Jae-Hoon's name, so I thought I'd respond
to Youn-Hee anyway, and hope the message
is passed on.

The idea of using Neighbor Discovery for DAD
is a good one, if it can be made to work.
Alper Yegin tried very hard to do this a while
ago (I talked to him about it before IETF55),
and there's one fatal flaw which cannot be
recovered using ND.

While the router knows about all of the hosts on the
link, it can indicate whether an address is unused.
This is the same principle used for MLD-DAD
(which has since expired... if you need the reference
contact me).

The issue is when a router fails or comes up on a link
for the first time, it cannot build a list of which hosts
are already on the link.
There is no ND message where all hosts (or even large
groups of hosts) must respond, which can be used to rebuild
ND state.

This means that the router may incorrectly allocate existing
addresses if there is a host that doesn't receive off-link
unicast packets at an address.

In MLD-DAD, state can be rebuilt using query messages, which
have no equivalent in ND.

If you wish to discuss this further, please
feel free to discuss this either here or on the DNA
list.

Greg Daley

[email protected] wrote:
> A New Internet-Draft is available from the on-line Internet-Drafts directories.
> 
> 
> 	Title		: Using Neighbor Caceh Entry for Duplicate Address 
> 			  Detection
> 	Author(s)	: J. Kim, et. al.
> 	Filename	: draft-hoon-mobileip-undad-00.txt
> 	Pages		: 14
> 	Date		: 2003-10-20
> 	
> The Duplicate Address Detection (DAD) procedure detailed by Neighbor
> Discovery Protocol (NDP) requires nodes to wait for a quantified time
> interval during which the configured address is checked for
> duplication in the connected link. This delay affects normal
> communication in a Mobile Node (MN) during the DAD time interval
> thereby hampering Fast Handoff. The expected use of Mobile IP on a
> wide scale and the need for a minimal time delay during the handoff
> process require alternate mechanisms for overcoming the DAD time
> interval. This draft presents a mechanism wherein the Access Router's
> (AR) Neighbor Cache Entry (NCE) is used to minimize the delay
> associated with the DAD procedure.
> 
> A URL for this Internet-Draft is:
> http://www.ietf.org/internet-drafts/draft-hoon-mobileip-undad-00.txt
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