Renewal of IP config.

[Bjørn Mork]

Dan Williams <dcbw at redhat.com> writes:
> On Thu, 2015-03-26 at 20:22 +0100, Markus Gothe wrote:
>> Does the modemmanager handle the case where a new IP configuration is handed out? Have we seen any cases like that???
>> 
>> Sierra Wireless had a lease time of 50 years (sic!) in their old sierra_net.c built-in DHCP-server.
>> 
>> AFAIK this is not an issue over PPP since it is just a tunneling protocol. But what about packet switched networks, like LTE?
>> 
>> GPT might be the keyword here... I heard  that some early techs like iBurst etc used ethernet over the air in the backhaul.
>
> ModemManager itself simply retrieves the IP configuration details from
> the modem and passes them to the IP configuration manager (eg,
> NetworkManager or something else) when the bearer is connected.  If
> there is any kind of "ip config changed" signal that the modem emits,
> then MM should listen to that, but I'm not aware of anything at the
> AT/MBIM/QMI/etc level.  Instead that's usually handled at the IP+ layers
> via DHCP or SLAAC.

MBIM supports reconfiguration:

 10.5.20 MBIM_CID_IP_CONFIGURATION
 ..
 Unsolicited Event: 
 InformationBuffer contains MBIM_IP_CONFIGURATION_INFO.  Whenever the
 MBIM function obtains updated IP configuration information, it must
 issue an Unsolicited Event to inform the host about the new value(s).

But I don't think it's currently possible to change address(es) of an
LTE PDN connection.  At least that's my understandig of how it works,
based on a very slack reading of RFC6459.  Quoting:


 5.1. IPv4 Address Configuration


   The UE's IPv4 address configuration is always performed during PDP
   context/EPS bearer setup procedures (on layer 2).  DHCPv4-based
   [RFC2131] address configuration is supported by the 3GPP
   specifications, but is not used on a wide scale.  The UE must always
   support address configuration as part of the bearer setup signaling,
   since DHCPv4 is optional for both UEs and networks.

 5.2. IPv6 Address Configuration

 ..

   Renumbering without closing the layer-2 connection is
   also not possible.  The lifetime of the /64 prefix is bound to the
   lifetime of the layer-2 connection even if the advertised prefix
   lifetime is longer than the layer-2 connection lifetime.



Bjørn