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Level 1: Cadet

VM networking problem on when modem in mobile mode.

Answered

Hi,

I had a weird problem recently that took a while to track down.

I have a few computers in the house, on one of which I run a few virtual machines on (both windows 10 and Fedora 30 - 32).

The host for the VMs is Fedora 32, and they are implemented with KVM/QEMU. The networking for the guests is NAT, and addresses for the guests are allocated via DHCP in the guest address space.

 

The setup was working fine for a number of months, but then out of the blue the VMs were no longer able to connect to the internet. But they were still able to connect to all of the other virtual and physical machines in the house. And all of the physical machines were able to access the internet normally.

 

If I disabled the connection to the Telstra NBN modem, and connected a iphone with hotspot on via USB to their host, all the VMs could communicate to the internet again.

 

To cut to the chase, it turns out that the NBN connection box had become unplugged from the power, and the NBN modem had switched over to mobile mode. (This was accompanied by the friendly green light on the front of the modem changing to blue, which I will admit I didn't notice.) Reinstating power to the connection box restored normal operation of the whole system, and all VMs can appily work over the internet again.

 

I am posting this in case someone else has the same problem, in the hope that it might save them some time, but also to seek some suggestions as to what network settings in modem/host/guests might avoid this issue.

TIA

 

 

 

 

 

 

 

1 ACCEPTED SOLUTION

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Level 24: Supreme Being
Level 24: Supreme Being
Accepted Solution

Re: VM networking problem on when modem in mobile mode.

By default the modem only has an IPv6 address on the WAN. Devices that only support IPv4 should still have internet access as the modem should support tunnelling of the IPv4 packets. I have found that on the Arcadyan modem (LH1000) tunneling doesn't work. The PDP  mode setting in the modem can be changed to IPv4v6 so that the modem has a IPv4 address on the WAN when in back up mode (Go to Advanced > Internet > LTE).

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3 REPLIES 3
Level 25: The Singularity
Level 25: The Singularity

Re: VM networking problem on when modem in mobile mode.

It's to do with the availability of external IPv4/IPv6 connectivity, which is different in mobile mode vs NBN mode.

Never be afraid to back yourself when trying new things, just always make sure you have 3 escape routes if things go wrong.
Highlighted
Level 24: Supreme Being
Level 24: Supreme Being
Accepted Solution

Re: VM networking problem on when modem in mobile mode.

By default the modem only has an IPv6 address on the WAN. Devices that only support IPv4 should still have internet access as the modem should support tunnelling of the IPv4 packets. I have found that on the Arcadyan modem (LH1000) tunneling doesn't work. The PDP  mode setting in the modem can be changed to IPv4v6 so that the modem has a IPv4 address on the WAN when in back up mode (Go to Advanced > Internet > LTE).

View solution in original post

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Level 1: Cadet

Re: VM networking problem on when modem in mobile mode.

Thanks  cl4, that was exactly the issue. I changed the PDP mode to IPv6v4, and all connectivity was there whether on HFC or mobile.

Thanks again for your help.

 

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