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

Hi Jaehoon and Ed,

jaehoon.kim wrote:
>>Jae-Hoon and Youn-Hee,
>>
>>I think there is another problem with this draft... the router doesn't
>>know when a host leaves the link (i.e. due to link movement), therefore
>>if the MN leaves link A to move to a new link B and then in some short
>>time (i.e. 20 seconds or so) returns back to link A, the router will
>>think that the MN never left link A, when the MN queries the router if
>>its care-of address is already in use the router will respond that it
>>is. This would cause the MN to fail to configure the care-of address it
>>used before on link A.
>>
>>Thanks.
>>- Ed
>>
> 
> Thank for your good comment.
> 
> In this case, router have a NCE for CoA. So, router never reply to MN.
> Refer to my draft.
> 
>    3.2 AR's requirement
>    -  Access router should reply to the sender which has sent NS message
>       with the 'A' bit set in the 4th reserved field in NA if access
>       router has no entry corresponding to the target address.
>       =====================================
>    4.1 Mobile node's operation
> 

The time which was mentioned by Ed may be the relevant
criteria (30 seconds is still within normal
ND cache timeouts).

If the router had an active neighbor cache entry
for the host (perhaps because of NUD or Higher
layer confirmation - it was sending packets to
the MN), then the cache entry would indeed be valid.

Leaving ND cache entries in the router for an arbitrary
period of time is problematic though.  For example,
I get off the same bus each morning to arrive at the
same desk, possibly using a different path on the way.

Assuming that address state still exists in the router
when I return, my Tuesday and Wednesday networking
experience is likely to be worse than my Monday one.
Even returning from getting a coffee may be frustrating.

If the NC entries aren't long term I can currently
see two solutions to keeping them in the cache
(and keeping state valid):

* Make address lifetimes sufficiently short that the addresses
   have a short lifetime, and must be reconfigured.

* Actively poll devices using NUD even if they are not
   receiving packets (maybe at longer than normal intervals).

The second solution may have significant battery life issues
in wireless computing environments (as MLD group membership
does anyway).

Greg