Host data interface IP configuration via DHCP vs via control channel.

Peter Naulls peter at
Tue Oct 25 13:15:50 UTC 2022

On 10/25/22 09:11, Aleksander Morgado wrote:
>> Assuming a mobile connection via any of the available control protocols
(QMI/AT/etc) has been initiated.
>> The mobile modem firmware has established a bearer connection and via the
(3GPP PCO -Protocol Control Options amongst others) an IPv4 address has been
received from the mobile network.  Now for the actual data interface on the host
a DHCPv4 client could be run to retrieve the IP address from the modem (this
assumes the Modem runs a DHCP server). But likewise via control protocol
(QMI/AT/etc) one could retrieve the IP address from the modem and configure the
data interface with the retrieved result.
> Yes. Not all modems have a DHCP server though, beware.

The DHCP is the upstream gateway, surely?  Anyway, it's certainly true that DHCP 
is not always provided.  But also, with a static IP assignment as it is done
in OpenWrt, there's no mechanism if the IP changes - this can happen due to
expiry of the IP, changing stations (i.e, a moving devicde) or other upstream 
network churn.  In such cases, you continue to be connected to the network, but 
lose IP connectivity unless you have another mechanism to watch for such changes.

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