Hey, > I need some help in establishing simultaneous interfaces to multiple APNs. > > I have an Ubuntu 20.04 system with a single cellular modem attached via USB > in an IoT application. My problem is that I need to drive traffic through two > different APNs when registered to the same cellular network. Each APN serves > a different purpose -- different services with different billing are to occur > on each. > > I've tried multiple ways to do this. While I can get connected with two APNs, > I can only get an interface name for one of the connections. I need a > separate interface name for each so that I can place the respective flow of > traffic through the appropriate interface and onto the correct APN. My > application needs both to be available simultaneously. Going back and forth > between building up and tearing down each of them is not an acceptable > solution. > > I tried three different things and none have brought happiness: > > (1) Using mmcli in debug mode with a set of AT commands for each APN: using > the sequence AT+GDCONT, AT+XGAUTH, and AT+CGACT with parameters relevant for > the first APN and then again with the sequence AT+GDCONT, AT+XGAUTH, and > AT+CGACT for the second APN. This is successful, and I obtain assigned IP > addresses for each APN. However, neither of the APNs are assigned to an > interface and I don't know how to funnel traffic to each. > > (2) I have used the bearer features of mmcli. I have run "mmcli -m > <modem-number> --create-bearer=<key-value pairs>" two times, each with the > proper key-value pairs for the respective APNs. When I later run "mmcli -m > <modem_number>", I see both bearers. I then run "mmcli -m <modem-number> > --bearer <bearer-number> --connect". This works the first time for the first > APN/bearer, and I have an interface assigned. But I get the following error > when next running " mmcli -m <modem-number> --bearer <bearer-number> > --connect" for the second APN/bearer: > error: couldn't connect the bearer: 'GDBusError: > org.freedesktop.ModemManager1.Error.Core.NotFound: No valid data port to > launch connection' > > (3) I've put multiple connection keyfiles in the > /etc/NetworkManager/system-connections directory. I run "nmcli con reload" > and then "nmcli --wait 120 con up id <name_of_first_connection>". This works > as I get connected to the first APN, get assigned an IP address, and get an > interface association (wwan0). However, when I run "nmcli --wait 120 con up > id <name_of_second_connection>", this works, but it displaces the first > connection, so I am only left with the second connection on interface wwan0. > The first connection is no longer available. > > My Ubuntu 20.04 system has mmcli 1.16.6 and nmcli 1.22.10. I could also > install mbimcli 1.24.8, although it is not currently part of the system image. > > Ideas on how to accomplish what I am after?
Your modem needs to be QMI or MBIM based, and you need to install ModemManager 1.18, which is the first version supporting multiplexing. Once you have that, you can: * run Modem.SimpleConnect() with"multiplex=required" Or: * start the ModemManager daemon with the additional --test-multiplex-requested option. My suggestion is to use the 2nd option, just start MM with --test-multiplex-requested so that any attempt to start a connection (e.g. via NetworkManager) will trigger the multiplex setup. When running with multiplex enabled, ModemManager will create a new virtual network interface for each APN connection, and then you can handle custom routing rules in the host for each of them. I talked a bit about this feature in the FOSDEM2022 talk earlier this year, if you're interested: https://fosdem.org/2022/schedule/event/mobile_modemmanager/ -- Aleksander https://aleksander.es
