4G modem: interfaces get IP but no connection

We're having a weird experience with a D-Link DWR-921 with an embedded LTE modem on 18.06.2.

We followed the guide on the wiki and it's ok, but just works with a single cell provider!

So we make the configuration working for Operator A, then we swap the SIM, change APN and PIN config, commit and restart the router. When we bring up the interface it gets an IP address but then it won't access internet, it doesn't even ping the default gateway received on the interface.

We thought any sort of configuration issue, like firewall or something like that, but if we just put back the old SIM and change the config it works immediately...

It seems to work just with Iliad (Italy). With other operators like TIM, Oh., Wind/Tre and they all behave the same: get IP but no internet access.

Any suggestion what I could check? Thanks

Many ISPs, especially wireless, don’t respond to pings.

The output of

ip link
ip addr 
ip route

would be where I’d start.

And the "gateway" isn't even the ISP. It's an arbitrary pool address, most likely assigned to another customer on the same PGW. Pinging it is pointless for any sort of connection test. Ping some other address which is known to answer.

I pinged and, and as a last test I tried pinging the gateway provided by the connection, which is a private /30 btw.

Right now I don't have a router handy to test the iproute2 commands above, but I will soon. From what I remember routes were correct, the default was ISP's one.

I forgot to mention that the same SIM cards placed into a phone have internet access.

My first tought is a bad APN, but I got the values from official websites. But does the connection goes up if the APN is wrong?

One other doubt: if the SIM has no PIN, shall I set it to '' or just set the value as empty?

No, it won't.

Get the APN from the screen of your working cell phone instead.

I haven't found the solution, and will probably not get one. The same SIM card works in another router, so it seems a problem of the single unit. Other than that, after restoring the original D-Link firmware it behaves the same: strenght signal but no connection.

If this page is right Iliad is the only provider that needs APN, username and password. For all other Italian ISPs you mentioned the username and password must/should be left blank. I wonder how you could make Iliad work if you only changed the APN. And if your router automagically obtained username and password for Iliad it should forget them and not store them anywhere for other ISPs.
btw I'm not Italian and I don't use 4G.

Hi, read my post.
It could work for you too.


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