Strange behaviour of Sierra Wireless MC7430

Aleksander Morgado aleksander at
Tue Oct 17 07:48:25 UTC 2017


> The MC7430 does behave very strange when I try to setup ip connectivity to
> it.
> When I bring the modem on line  qmicli -d /dev/cdc-wdm0
> --dms-set-operating-mode=online I see the modem attaching on our cell and in
> the Attach accept message it gets an IP address. That address is not
> automatically added to the wwan0 interface. Verification of the
> nas-serving-system returns the following info
> qmicli -d /dev/cdc-wdm0  --nas-get-serving-system
> [/dev/cdc-wdm0] Successfully got serving system:
>     Registration state: 'registered'
>     CS: 'attached'
>     PS: 'attached'
>     Selected network: '3gpp'
>     Radio interfaces: '1'
>         [0]: 'lte'
>     Roaming status: 'off'
>     Data service capabilities: '1'
>         [0]: 'lte'
>     Current PLMN:
>         MCC: '1'
>         MNC: '1'
>         Description: 'Test1-1'
>     Roaming indicators: '1'
>         [0]: 'off' (lte)
>     3GPP location area code: '65534'
>     3GPP cell ID: '769'
>     Detailed status:
>         Status: 'available'
>         Capability: 'cs-ps'
>         HDR Status: 'none'
>         HDR Hybrid: 'no'
>         Forbidden: 'no'
>     LTE tracking area code: '1'
>     Full operator code info:
>         MCC: '1'
>         MNC: '1'
>         MNC with PCS digit: 'no'

At this stage, from the point of view of the user, you just got
registered to the network but no data call was explicitly started by
the user (regardless of whether the modem got an IP from the LTE
network, which always happens as soon as the modem gets registered in

> However when I try to get information about the IP address using  qmicli -d
> /dev/cdc-wdm0  --wds-get-current-settings I get
> error: couldn't get current settings: QMI protocol error (15): 'OutOfCall'

As above, the user didn't start explicitly a data call, so OutOfCall error.

> Until a few days ago this would just return me the assigned IP address. If I
> than start the network (can someone explain me what this does) I get the
> following  qmi-network /dev/cdc-wdm0 start

"Start the network" means to start a data call explicitly. The user
requests a data call to the modem and gets assigned a "session id" for
the call.

> Loading profile at /etc/qmi-network.conf...
>     APN: internet
>     APN user: unset
>     APN password: unset
>     qmi-proxy: no
> Checking data format with 'qmicli -d /dev/cdc-wdm0 --wda-get-data-format
> '...
> Device link layer protocol retrieved: raw-ip
> Getting expected data format with 'qmicli -d /dev/cdc-wdm0
> --get-expected-data-format'...
> Expected link layer protocol retrieved: raw-ip
> Device and kernel link layer protocol match: raw-ip
> Starting network with 'qmicli -d /dev/cdc-wdm0
> --wds-start-network=apn='internet'  --client-no-release-cid '...
> Saving state at /tmp/qmi-network-state-cdc-wdm0... (CID: 35)
> Saving state at /tmp/qmi-network-state-cdc-wdm0... (PDH: 62876480)
> Network started successfully

At this point the network was started, i.e. the data call was established.

> If I than ask for the current settings qmicli -d /dev/cdc-wdm0
> --wds-get-current-settings I get
>  Current settings retrieved:
>            IP Family: IPv4
>         IPv4 address:
>     IPv4 subnet mask:
> IPv4 gateway address:
>     IPv4 primary DNS:
>                  MTU: 1500
>              Domains: none

These are the settings that the modem requires to be set in the
network interface. Two options here: either IP settings assigned by
the network (transparent/bridge mode) or assigned by the modem itself
(router mode).

> The first thing I noticed is the netmask. I don't know where the modem is
> getting this from but it is definitely not coming from the core network.
> Anyway if I assign to the wwan0 interface I see that wwan0
> is configured but the Link encap is UNSPEC

The netmask is just so that the next hop (the gateway IP that the
modem assigned to itself) is in the same subnet is within the range
defined by the netmask.

> wwan0     Link encap:UNSPEC  HWaddr
> 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
>           inet addr:  P-t-P:  Mask:
>           inet6 addr: fe80::d37a:aed3:aeb:4d4/64 Scope:Link
>           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:9 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:1000
>           RX bytes:0 (0.0 B)  TX bytes:504 (504.0 B)

The UNSPEC link encap is because this interface is in raw-IP mode;
i.e. no ethernet headers, just IP packets.

> If I than try to ping from my raspberry pi which has the modem connected to
> a host behind the core network, I see nothing arriving in the GTP tunnel on
> core network, however when I ping from the host behind the core network to
> I get replies from the ping , I even see them in both
> directions going through the GTP tunnel but on my linux interface (wwan0) on
> the rasberry pi I don't see any packet being received or transmitted. So it
> looks as if the Sierra Wireless card is responding to the pings but it is
> not offering its IP capabilities to the my Linux.

How are you doing the ping?
Do you have rp_filter disabled for the WWAN?


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