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Note: This is a "cross-post", I asked this same question on "superuser" StackExchange site, but without obtain any answers, just a comment (now curiously disappeared).

I've thought this site is better for network related questions, so here we are... Hope this was a good idea. Let's come to my question:

A user is trying to configure a usb dongle (ZTE K3806-Z - Vodafone) for mobile broadband under Linux and reports issues with wwan0 interface.

USB device interface related to mobile broadband network is recognized and bound by cdc_ether kernel module (follows usb-device output). I: If#= 5 Alt= 0 #EPs= 1 Cls=02(commc) Sub=06 Prot=00 Driver=cdc_ether

He reports that using Networkmanager connection seems ok (wwan interface addressed etc, but he can't browse the web nor make network apps work at all). So I suggested to report output of various networking tools. Her we have 'ip address show dev wwan0'.

4: wwan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether 02:fa:a8:34:86:69 brd ff:ff:ff:ff:ff:ff inet 47.53.62.249/24 brd 47.53.62.255 scope global wwan0 valid_lft forever preferred_lft forever inet6 fe80::fa:a8ff:fe34:8669/64 scope link valid_lft forever preferred_lft forever

And routing table (ip route show): default dev wwan0 proto static 47.53.62.0/24 dev wwan0 proto kernel scope link src 47.53.62.249 metric 7 127.0.0.0/8 dev lo scope link

If he tries to ping a numeric ip (example 8.8.8.8): From 47.53.62.249 icmp_seq=1 Destination Host Unreachable From 47.53.62.249 icmp_seq=2 Destination Host Unreachable

Where could be the matter?

I thought something gateway related, cause I'm also using wwan0 interface to internet (3g-mobile broadband), but with different ISP that assigns private IP to my interface, here my routing table: default via 10.188.246.97 dev wwan0 metric 203 10.188.246.96/29 dev wwan0 proto kernel scope link src 10.188.246.99 10.188.246.96/29 dev wwan0 proto kernel scope link src 10.188.246.99 metric 203 127.0.0.0/8 dev lo scope link

Anyway in this case my default gateway address is clear: 10.188.246.97, while other user doesn't report any gateway.

I'm not an expert about network troubleshooting so an answer would be greatly appreciated. Thanks in advance!

PS. My usb dongle use qmi_wwan linux driver for broadband interface, and I establish internet connection using qmi_cli tool and dhcp. What command line tool he could use to connect his dongle that support cdc_ether driver?

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Yes, that routing table shows there is no route to 8.8.8.8. The only routes are the 47.53.62.0/24 subnet and the loopback. A default (0.0.0.0/0.0.0.0) route (or a number of more specific routes if you prefer) needs to be added for the gateway that exists on the 47.53.62.0/24 subnet.

There are many other points of failure after this, but this is certainly the first step forward.

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  • Thank you. Since I'm not so expert... what "ip" command would you say to use? I would try "ip route del default" to delete actual default route; "ip route add default dev wwan0 via ?.?.?.?" to add new route. But I don't have any info about gateway address now... Is this info needed or we have yet enough elements to solve?
    – Joe
    May 27, 2015 at 8:11
  • Yes, you need to first find out the default gateway from whoever manages that subnet (I'm assuming the IP is static). If the IP comes from DHCP, then it should send you a gateway too. Considering that you don't know the gateway, it's possible too that you are trying to configure the interface statically when it should be configured using DHCP instead. You do not need to delete any route. Just add the default gateway. Your command above looks good, but you'll probably also want to add it to the interface script so it persists on reboot, which is different in different distros.
    – jhenn
    May 27, 2015 at 13:36

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