Subject: Re: I-D Action: draft-kaiser-nd-pd-00.txt

From: Brian E Carpenter <[email-masked]>
Date: Tue, 23 Oct 2012 13:19:30 +0100

I realised while reading this draft that I just don't understand
its operating model. It refers to the "requesting" router supplying
Prefix Collection and Prefix Information to the delegating router:

>    When requesting prefixes a requesting router MUST add for each
>    requested prefix a Prefix Information in the Prefix Delegation option
>    of the RS message.  

However, by definition the requesting router doesn't know what prefix(es)
it will be given. So surely all it can ask for is N unspecified prefixes
of given lengths?

It also says:

>    PC_ID:           An unique identifier of the Prefix Collection.  The
>                     PC_ID MUST be unique among all PC_ID known by the
>                     requesting router.

How can the requesting router provide this in its REQ message? By guessing?

> 11.  Security Considerations
> 
>    TBD

OK, but since a vehicular network is open to any one of millions of
unmanaged devices, this will need to be *very* convincing, especially
in preventing DOS.

Regards
   Brian Carpenter

---

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 25 Oct 2012 18:03:49 +0200

Hello Brian,

Thank you for the email.  Please see below some comments.

> it will be given. So surely all it can ask for is N unspecified prefixes

Right, this may be wrong.

I checked the document and it misses, I think, something important. The
first and most naïve request of a prefix by a Requesting Router should
have all bits zero and maybe the prefix length 0, or around 64.

Would this be ok?

> How can the requesting router provide this in its REQ message? By guessing?

I think the PC_ID is generated by the requesting router (not by the 
delegating router), just as with IA_ID, no?

> unmanaged devices, this will need to be *very* convincing, especially

I agree.  We currently try to understand these threats, and especially 
how they are specific to ND, to prefix delegation and to new flags we add.

We may add more threat descritpion in the next versions of the draft.

Alex

---

From: Brian E Carpenter <[email-masked]>
Date: Thu, 25 Oct 2012 19:25:58 +0100

> have all bits zero and maybe the prefix length 0, or around 64.

Wouldn't the request typically be for a /48 or a /56? If I'm renumbering
an existing network, I will want a prefix that is no longer than what
I already used.

I wonder whether an expensive BMW will always request a shorter prefix
than a Nissan Versa.

> delegating router), just as with IA_ID, no?

Ah yes, I simply misread the text, sorry!

   Brian

---

From: Alexandru Petrescu <[email-masked]>
Date: Fri, 26 Oct 2012 12:10:47 +0200

Le 25/10/2012 20:25, Brian E Carpenter a écrit :
[...]
>> I checked the document and it misses, I think, something important.
>> The first and most naïve request of a prefix by a Requesting Router
>> should have all bits zero and maybe the prefix length 0, or around
>> 64.
>>
>> Would this be ok?
>
> Wouldn't the request typically be for a /48 or a /56? If I'm
> renumbering an existing network, I will want a prefix that is no
> longer than what I already used.

The 'end' router in a Leaf Vehicle would probably need 1 or 2 /64 for
its own in-vehicle links.  Or maybe a single /63 to make these 2 /64s
our of it.  Or similar.  This MR-LV would not sub-delegate to other
vehicles.

On another hand, the router in an Internet Vehicle IV would use
DHCPv6-Prefix-Delegation to obtain an as short prefix as possible (/48,
/56) because it knows it would 'sub-delegate' to other LVs - it has
dedicated interfaces for that.

> I wonder whether an expensive BMW will always request a shorter
> prefix than a Nissan Versa.

That is an excellent comment.

The IV would have a SIM card with precise billing scheme; existing more
expensive cars have higher subscription plans.  One would expect a large
BMW connected to e.g. T-Mobile to be more likely to obtain a shorter
prefix (or several longer prefixes) than a cheaper car.

On another hand, the LV without a SIM would be subject to more flexible
billing plans, like with free-access WiFi but advertisement, and where
the notion of longer or shorter prefix would less be related to the cost
of the vehicle.

I think the ND-PD happening between IV and LV would not put restrictions
on the length of prefix requested or allocated.

Let me add the the size and cost of vehicle is not much related to how
much electronics and computers it has inside.  Smaller vehicles are more
and more automated and full of devices.  Also, it may be that new small
vehicles coming out these days have much more computers inside than an
older but large and comfortable sedan.

Alex

>>> It also says:
>>>
>>>> PC_ID:           An unique identifier of the Prefix Collection.
>>>> The PC_ID MUST be unique among all PC_ID known by the
>>>> requesting router.
>>>
>> I think the PC_ID is generated by the requesting router (not by
>> the delegating router), just as with IA_ID, no?
>
>>> OK, but since a vehicular network is open to any one of millions
>>> of unmanaged devices, this will need to be *very* convincing,
>>> especially in preventing DOS.
>>
>> I agree.  We currently try to understand these threats, and
>> especially how they are specific to ND, to prefix delegation and to
>> new flags we add.
>>
>>> Regards Brian Carpenter