No Internet access. Asus RT-AX68U, 3004.388.9_2, Dual WAN, Secondary WAN - USB

[Igor]

Asus RT-AX68U, fw 3004.388.9_2.

I use the main Internet access via Ethernet. It works without problems.

Today I checked the backup access via USB modem HUAWEI E3372h-320 (there were no problems before).

I disconnected Ethernet, the USB modem automatically connected.

Jul  9 11:06:47 kernel: eth0 (Int switch port: 3) (Logical Port: 3) (phyId: c) Link DOWN.

Jul  9 11:07:40 wan_up: Restart DDNS
Jul  9 11:07:40 dhcp_client: bound 192.168.8.108/255.255.255.0 via 192.168.8.1 for 86400 seconds.

But there was no Internet access.

How can I find the source of the problem?

Checking from the modem (GUI access):

Checking from the router (ssh access):

# ping google.com

PING google.com (64.233.163.101): 56 data bytes
ping: sendto: Network is unreachable

# ebtables -t broute -L --Lc
Bridge table: broute
Bridge chain: BROUTING, entries: 0, policy: ACCEPT

 

[Igor]

I found the cause of the problem. When connecting a HUAWEI E3372h-320 USB modem, there is no mirroring of the modem's DNS to the router address. For example, DNS from 192.168.8.1 (modem) is not associated with 192.168.1.1 (router).
There was no such problem before. If I connect an Android smartphone instead of HUAWEI E3372h-320, then there is no such problem. The problem is only with HUAWEI E3372h-320 on the current router firmware.

 

[Igor]

Please tell me how to enable DNS redirection from a modem to a router?

UPD.
When connecting a smartphone:
# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.42.129 0.0.0.0 UG 0 0 0 usb0

When connecting a HUAWEI E3372h-320 USB modem:
# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.8.1 0.0.0.0 UG 0 0 0 eth7

 

[Igor]

Replaced the USB modem from E3372h-320 to E3372-325, I no longer see problems with DNS.