Re: comments/questions on draft-yegin-dmm-ondemand-mobility-00

Alper,

On Jul 24, 2013, at 11:58 PM, Alper Yegin <[email protected]> wrote:

> Jouni,
> 
>>> 
>>>> Alper,
>>>> 
>>>> I read the draft and have few quick comments and questions. Interesting
>>>> draft by the way. In Section 3.1. it says:
>>>> 
>>>> "- Access Network Anchored Address
>>>> 
>>>> This type of IP address provides IP session continuity but not IP
>>>> address reachability."
>>>> 
>>>> Why is that? What makes IP(v6) address unreachable (I assume from 
>>>> Internet side)? I would like to see the rationale described here
>>>> for this reachability assertion.
>>>> 
>>> 
>>> 
>>> IP Address Reachability is defined as follows:
>>> 
>>>  IP address reachability: The ability to maintain the same IP address
>>>  for an extended period of time.  The IP address shall stay the same
>>>  across independent IP sessions, and even in the absence of any IP
>>>  session.  The IP address may be published in a long-term registry
>>>  (e.g., DNS), and it shall be available for serving incoming (e.g.,
>>>  TCP) connections.  IP address reachability is essential for mobile
>>>  hosts to use specific/published IP addresses.
>> 
>> 
>> I can read that from the draft but it still does not answer my question.
>> Say, I get an ANAA and the either the MN or the AN does dynamic DNS update.
>> Assuming the AN does not intentionally block incoming connections for 
>> ANAAs the MN can be reachable. What is the rationale to rule out incoming
>> connections? I recon you also mix the "IP address shall stay the same
>> across independent IP sessions" with your definition but IMHO that has
>> very little to do with reachability.
>> 
> 
> Yes, in the case of dynamic DNS there's "reachability".
> But we need to understand *what* is reachable.
> 
> When HNAA is used: The IP address stays reachable. 
> When we let the IP address change but keep using dynamic DNS: The FQDN stays reachable.

I could argue that HNAA is not stable enough to be considered
reachable as per how the draft describes it, especially in the
case of mobile devices. One flap on the wireless connection and
the address is likely to change.

> These are two different types of reachability. 
> And they are not equivalent.
> The latter has issues: Cannot converge fast, and does not work all the time (remote hosts do not keep querying the DNS just in case their peers have changed IP address… They cache DNS results…)

IMHO the difference between the ANAA and HNAA reachability is 
just the timescale. Even if the ANAA is likely to change more
frequently, there should not be a reason to state that it is
not reachable. I would rather focus on the "address stability"
or alike when coming up with the terminology. Say, your MN is
most of the time stationary (like most MNs are today) and
gets and ANAA. As long as the movement of the MN is within
a limited L2 area, its ANAA does not really differ from HNAA,
from the reachability point of view.

- Jouni

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> Alper
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>> - Jouni
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