MC7455 doesn't get address with dhcp


I’m having trouble getting network address for MC7455 module using DHCP client on linux device. We are using MBPL R24 and drivers that come with it. As a work around I query the address with SLQSGetRuntimeSettings and set that address to interface manually. So, network provides address to MC7455 modem, but for some reason DHCP client isn’t able to get it.

We used to have Gobi drivers for MC7455 modems and then there wasn’t any problems with DHCP client. Also, if I now put EM9190 modem to that same system it doesn’t have any issues with DHCP client. DHCP client is able to get the address that network has provided.

So, what could be wrong with MC7455? Linux version is 4.19.168 and MC7455 FW version is
SWI9X30C_02.33.03.00 r8209 CARMD-EV-FRMWR2 2019/08/28 20:59:30

br, Sami

have you tried “sudo udhcpc -i wwan0” ?
Or you are using dhclient?

Yes, I’m using udhcpc, but it will never get the address. It will just keep sending discoveries but doesn’t seem to get any offers…

udhcpc: started, v1.30.1
udhcpc: sending discover
udhcpc: sending discover
udhcpc: sending discover
udhcpc: sending discover
udhcpc: sending discover

I remember there is no such issue with my test here:

First of all, I don’t have that raw_ip file on my system. I think I had it but now that we are using mbim interface, it isn’t there anymore.

Config Index: 1
Config Type: 1 (Generic)
Interface bitmask: 0000100D (diag,nmea,modem,mbim)

But on the other hand, same goes with EM9190 module. There is no raw_ip file for it either, and it is also configured to use mbim instead of rmnet. But still it works with DHCP client without any problems…

Do you see problem with rmnet?
Or issue only happens on mbim?

I haven’t been able to verify that. I can’t connect to network, now that modem has been configured to use rmnet. It should be registered, but still it says that no network service.

Current Time: 5477 Temperature: 35
Reset Counter: 2 Mode: ONLINE
System mode: LTE PS state: Attached
LTE band: B3 LTE bw: 20 MHz
LTE Rx chan: 1300 LTE Tx chan: 19300
EMM state: Registered Normal Service
RRC state: RRC Idle
IMS reg state: No Srv

PCC RxM RSSI: -71 RSRP (dBm): -100
PCC RxD RSSI: 0 RSRP (dBm): 0
Tx Power: – TAC: 0FAA (4010)
RSRQ (dB): -9.3 Cell ID: 022D1915 (36509973)
SINR (dB): 6.4


+CME ERROR: no network service

did you follow the procedure?

  1. sudo qmicli --device=/dev/cdc-wdm0 --wds-noop --client-no-release-cid

I don’t have that qmicli available right now, so I skipped that one. What does it do exactly? Is it manadatory to be able to connect to network?

I added qmicli to my system. Lets see if it goes better with it…

It seems to work if modem is using rmnet:

udhcpc -i wwan0
udhcpc: started, v1.30.1
udhcpc: sending discover
udhcpc: sending select for
udhcpc: lease of obtained, lease time 7200

then is it ok to use RMNET as use case?

You also can try this script to have DHCP on MBIM interface:

./mbim-set-ip /dev/cdc-wdm0 wwan0

Well, that script does basically the same thing as my own link manager as a workaround for this dhcp problem. It queries address from modem and sets it to interface and It’s working fine. But I was just curious about why the dhcp client wouldn’t work in this case. It should on my opinion and it does when using for example EM9190 modem.

I don’t think that rmnet is an option for us. Using that creates a point to point interface and that turned out to be a problem for some third party SW that we are using.

ip link show wwan0
17: wwan0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN mode DEFAULT group default qlen 1000

ok, maybe you need to use that workaround

Hmm, yes probably… But I would really like to understand why this doesn’t work. There should be a dhcp server running inside that modem, right? Is there a way to verify if it is running or not?

I don’t know, as it works on RMNET, maybe some FW problem on MBIM…