Re: DHCPv6-PD is fine

[Alexandre Petrescu <[e-mail]>]

This is a personal point of view, I am not employed at manufacturer or
operator.

Le 09/11/2020 à 22:23, Ted Lemon a écrit :
> On Nov 9, 2020, at 4:00 PM, Havard Eidnes 
> <he=[e-mail] 
> <mailto:he=[e-mail]>> wrote:
>>>> From what I've been reading in this thread, in the mobile
>>>> world the problem isn't DHCPv6-PD, but the cellular world
>>>> having not adopted it, or even blocked it (ref discussion of
>>>> mobile modems blocking DHCP packets).
>> 
>> Is this lack of flexibility for all intents and purposes imprinted 
>> into silicon?  That would ... be an extremely effective road-block 
>> for practical deployment if one wanted to make a change where DHCP 
>> should additionally be used.
> 
> I’m having trouble envisioning how this would even be possible. Is 
> there an IP stack on the chip that has a firewall in it that blocks 
> DHCP?

Yes.

> This woud be surprising.

YEs to me too it was surprising to see how many things these modems do.

I was surprised first when my laptop sent a DHCP request, received an
answer, but the operator told me they did not receive such a request and
they did not generate an answer either.  It's because there was a DHCP
proxy in between that I could not see.  It's on the modem.

There is a whole operating system running in modern modems of
smartphones.  They have their own IP addresses inside.  Some times they
even run DHCP servers inside.

Looking at the open source efforts to make an OS for these modems it is
possible to get a hint of how advanced they are.  IIRC one is called
Hexagon MiniVM.

> Why would they go to that effort?

In order to protect (some humans at some computers at some) operator.

The legislation requests that the owner of a smartphone has access to
that smartphone, i.e. to log in and install whatever s/he wishes; as a
side note this is different than CPEs where the legislation only
requests the GPLed source codes of CPE to be made available upon request.

On these smartphones, a malicious user might install malicious software
that could attack the (~) operator.  Other than outright vicious attacks
some programmers might want to play with a home made DHCP client on the
ARM part of the smartphone (not the modem).  That client would disrupt
functioning of the already exisitng DHCP server running in the modem.  I
suspect that is why smartphone manufacturer, under guidance of modem
manufacturer and in agreement with (~) operator, effectively block UDP
port numbers of DHCPv6.  They block other people's DHCP and let only
their own non-documented variant of DHCP proxy through.

That is my supposition, or rather a speculation.  It means that I might 
be wrong.  But that does not improve the situation of absence of 
DHCPv6-PD in smartphones.

Alex

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