Maintaining connectivity between multiple devices

Aleksander Morgado aleksander at
Mon Feb 6 13:50:26 UTC 2017


>>> 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.
>> Beware when using raw-ip; your DHCP client may not know how to setup
>> the IP address in the ethernet-header-less interface. I.e. you could
>> manually configure the IP settings you got in
>> --wds-get-current-settings instead of relying on HDCP.
> Alright. Is it too early to use raw-ip? Unfortunately, I see a lot of other
> (unrelated) issues with Linux 4.9, which may force me to switch back to
> 4.4.8 and 802-3 for now.

It isn't too early to use raw-ip; it really depends on whether your
modem allows any other mode. E.g. the MC74xx/EM74xx family only work
in raw-ip mode.

>>> 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...
>> I'm still curious about how you manage multiple SIM cards on the same
>> device...
> See above :-) However, the question is more about switching between
> modems/interfaces that between SIM cards. The SIM switch functionality is
> working fine.

I think it really depends on whether the network operator likes
'silent' connections or not (e.g. the modem is connected but no
traffic goes through because the default route is set to some other
place). I'd bet it works ok in the general case, although not sure.
For the multi-modem setups I've worked with, when only one modem is
set to work at a time (e.g. via default route), I usually suggested
one device connected only (e.g. to avoid unnecessary power consumption
on the unused modems). Although it also depends on how quick you want
to detect the connection failure and switch to the other one. I think
it really depends on your specific needs.


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