Re: New Version Notification for draft-koodli-ipv6-in-mobile-networks-02

[Rajeev Koodli <rkoodli@cisco.com>]

On 4/19/10 2:24 PM, "teemu.savolainen@nokia.com"
<teemu.savolainen@nokia.com> wrote:

>> If PGW includes a Deferred Address Allocation PCO in Create Session
>> Response
>> (and hence no IPv4 address in it), the host has to do DHCP.
> 
> Incorrect. Standard does not allow network to behave that way.

Agree, I wrote too soon. UE includes a PCO for DHCP which is carried in
Create Session Request.


>> Yes, some hosts do this based on application trigger. OTOH, you could
>> initiate DHCP right away (after attach) but the network could use
>> shorter
>> lease times.
> 
> Right, some hosts may, but not all. Especially those that don't do DHCP for
> 3GPP.
> 

What about the laptops with built-in 3G/4G or using UE as a modem?

> 
> Yes, but this is *may* per 3GPP TS 23.401. Your draft should be more explicit
> in telling that the percentage of host population that actually implements the
> *may* part is unknown for time being.
> 

I would rather say that DHCP is optional but a provider may require it to be
used.


> 
>> Let us try to separate the issues here.
>> 
>> 1. When DHCP is initiated. 1a) right after attach, 1b) as a response to
>> an
>> application trigger. Your concern is with 1b) right?
> 
> Of those two, my concern is 1b.
> 
> But the bigger concern is talking so much about DHCP that is optional by
> standard.
>  

Actually I would have to talk much now (there are just a couple of sentences
currently) :-)

Optional does not mean that it is not used (and vice versa).
In our context here, it is up to a service provider to require it if they
feel there is value in using it for their IPv4 address management.


>> 2. Regardless of 1a), 1b), a network could use lease times of its
>> choice
>> right (subject to pros/cons)?
> 
> Right. But the lease time is IMHO mostly irrelevant, if the host is stubborn
> to just renew even if it hasn't applications running. Thus the host would have
> to be smart enough not to renew if it doesn't have imminent need for IPv4.
> 

Sure, hosts can do clever stuff. Providers may have compliance requirements
if a node is to be on their network OTOH (I am not justifying the approach
itself, but pointing it out).

>> Hmm..interesting. Going by this, one could argue that DHCP with shorter
>> lease times is host based transition, and the network cleaning up
>> PDN/PDP sessions due to timers is network-based transition :-)
> 
> As said, DHCP with short lease times and network cleaning PDP sessions does
> help nothing if the host has decided to keep IPv4 connection up "just in
> case", and instantly renews what network tries to bring down. You must have
> host support not to open "just in case".
> 

See above. In summary, for a significant population of hosts, session timers
may be useful. For "just in case" hosts, this may be less useful.

-Rajeev


>> IMO, a mobile network provider may require DHCP from vendors. Not all
>> providers may go for it, but some may find it useful.
> 
> This is absolutely true. However, the standard does not mandate DHCP. Hence
> the standard documents, like this draft, should be clear on what is certainly
> available by standards compliant devices (that implements musts and shalls),
> and what may require something extra (i.e. what is possible by standard, but
> not necessarily supported by default - the mays).
> 
> Best regards,
> 
> Teemu