Re: 回复： DMM API

Hi, Alper,

Sorry for interfering but I have a few points where I agree with Dapeng.

Le 25/03/2015 16:43, Alper Yegin a écrit :
> Hello Dapeng,
>
>
> On Mar 25, 2015, at 11:01 PM, Dapeng Liu wrote:
>
>> Hello Alper,
>>
>> I still have the following comments:
>>
>> 1. Regarding the definition of “fixed IP address” in the draft:
>>
>>   “- Fixed IP Address
>>     This is what standard Mobile IP provides with a Home Address (HoA).
>>     The mobile host is configures a HoA from a centrally-located Home
>>     Network.  Both IP session continuity and IP address reachability are
>>     provided to the mobile host with the help of a router in the Home
>>     Network (Home Agent, HA).  This router acts as an anchor for the IP
>> address of the mobile host.”
>>
>> If this is equal to HoA, then RFC5014 already cover that. We do not
>> need to repeat it here with another name.
>>
>
>
> This is not equal to "HoA".
> This is equal to "HoA permanently allocated on a HA in the core network"
> (as opposed to "HoA temporarily allocated on a HA in the access network")

So that's a HoA, and RFC5014 already covers that, right?

>> 2. Regarding the definition of “sustained IP address” in the draft:
>>
>> "- Sustained IP Address
>>
>>     This type of IP address provides IP session continuity but not IP
>>     address reachability.  It is achieved by ensuring that the IP address
>>     used at the beginning of the session remains usable despite the
>>     movement of the mobile host.  The IP address may change after the
>>     termination of the IP session(s), therefore it does not exhibit
>>     persistence.
>> "
>> There is no clear dividing line between fixed IP address and sustained
>> IP address. Whether the IP address is used for reachability is not
>> determined by the IP address itself. For example, even when the MN get
>> a HoA, after it moves to another location of the network, it may
>> decide to release current HoA and get another HoA, in this case the
>> "fixed IP address" becomes a "sustained IP address".
>>
>
> If the IP stack on the host releases the IP address, then of course it's
> not a "fixed IP address".
> Please see the definitions of these terms in the I-D.
>
>
>> Further more, the reachability normally is implemented by domain name
>> instead of IP address. For example, we reach “Google” by its domain
>> name, never by it’s server’s IP address.
>>
>> Using temporary private IP address we can also achieve the goal of
>> “reachability”. For example, using dynamic DNS, as shown in
>> http://hsk.oray.com/ , it can  provide reachability even the host get
>> a private IP address.
>>
>
> You had said this before, and I had explained it.
> Nevertheless, let me recap:
> You cannot ensure an ongoing IP flow continues w/o interruption if you
> simply rely on dynamic DNS. Ongoing flows break even if you update the DNS.

But Dapeng talks about reachability, not about session continuity.  In 
that sense he's right, no? (DNS updates ensure reachability upon address 
change).

Even I would go as far as to say that _some_ application flows will 
resist to changes in that IP address and get restarted with the new 
address if that DNS update process was performed.

This is because the concept of 'flow' is very much ambiguous.  Very 
rarely a read in packet dump can show 'flows' as we talk commonly about 
them in the DMM discussions.  It is for this reason that there is no 
option in Wireshark that groups packets in 'flows', like a mail reader 
would group messages into 'conversations' or 'threads'.

It is for this reason too that firewall rules trying to be smart and 
identify 'flows' before blocking them very often fail, even if we do 
Deep Packet Inspection.  People always find ways to 'drill' through 
these rules.

> Furthermore, even if you ignore the ongoing flows, also note that DNS
> clients have a cache, hence a dynamic DNS update cannot be
> instantaneously reflected on the hosts.

I can agree to that.  I guess though there may be forced updates on 
these caches, or that the timers can be configured shorter in domains 
supporting mobility.

> So, you cannot provide full mobility solution by relying on dynamic DNS.

We dont know what full mobility is, and DNS updates is a good tool to 
provide reachability and session continuity, in some cases.

Alex

>
>
>> 3. Regarding the definition of “nomadic IP address”:
>>
>> “- Nomadic IP Address
>>     This type of IP address provides neither IP session continuity nor IP
>>     address reachability.  The IP address is obtained from the serving IP
>>     gateway and it is not maintained across gateway changes.  In other
>>     words, the IP address may be released and replaced by a new IP
>>     address when the IP gateway changes due to the movement of the mobile
>> host.”
>>
>> Seems this IP address is the IP address that we normally used in most
>> cases. If this is the case, why we need a new name for it?
>>
>
>
> If you don't name it, how would you refer to it in this context?
>
>
> Alper
>
>
>>
>> --
>> Dapeng Liu
>>
>> 在 2015年3月25日 星期三，下午2:02，Alper Yegin 写道：
>>
>>> Hello Dapeng and Alex,
>>>
>>> I hope you had a chance to digest our responses to your comments and
>>> questions about the API work.
>>> If you have any remaining issues, please let us know over the email
>>> at your earliest convenience.
>>> It'd be good if you can articulate them in detail.
>>>
>>>
>>> Thanks.
>>>
>>> Alper
>>
>


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