Renewal of IP config.

Dan Williams dcbw at
Thu Mar 26 14:03:55 PDT 2015

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.

If the modem uses DHCP, then the IP configuration manager is responsible
for renewing the DHCP lease.  In NetworkManager, that depends on the
DHCP client you have selected, which could be dhclient, dhcpcd, or our
internal implementation.  That DHCP client waits for the correct
renew/rebind timeouts and renews the lease and gets the new IP
configuration info.

For IPv6 SLAAC, either the kernel or the IP configuration manager is
responsible for listening to the router advertisements and updating the
interface's IP configuration from that info.


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