Maintaining connectivity between multiple devices
kasper at holtze.dk
Sun Feb 5 21:31:54 UTC 2017
Sorry if this is the wrong place to ask. I'm working on a solution which
has multiple interfaces for Internet connection. Two QMI modems
(MC7304), a LAN interface and a WiFi interface. The questions is
primarily regarding the modems.
Each modems has two SIM cards, and I've build a small piece of software
to switch between these, and all of the interfaces. All the switching is
working fine. I am switching between modems/interfaces by
opening/closing the interfaces (ifup/ifdown), and that way making sure
the right interface is in use. Only the interface which "should be used
right now", is active.
However, I am seeing issues getting connectivity through the modems -
sometimes I cannot get an IP address from the modem, even though I can
see that the modem is connected and has an address.
I have recently switched from 802-3 to raw-ip, by upgrading Linux from
4.4 to 4.9. That seems to work fine, and /sys/class/net/wwanX/qmi/raw_ip
is always set to Y (is echo'ing Y to this the right way to go?).
I configured the modems to use autoconnect, so that even if there's
issues with the software, the modems itselfes will connect to the internet.
So, in the hunt of the most stable solution, my questions are:
- I'm wondering if the approach is the best, or if I should not
open/close the interfaces all the time, and just switch the default
gateway? Or using libqmi connect functions, and disable autoconnect...
- If I just connect the modems at boot, using autoconnect, will the
modems reconnect if they are out of coverage for a while? Will the DHCP
client automatically fetch the new IP address when the connection is
restores? What if it moves cross-border, will it restore connectivity
automatically? I guess I could just test this, but it would be nice to
know some theory about it.
Thank you very much!
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