I have an odd issue with a RUT950 which is deployed in an installation. The router is connected to 4G/LTE, and it works as an L2TP/OVPN server and it forwards some ports for a couple of web interfaces for other devices on the network. It's accessed remotely using a DDNS domain. This has worked well until recently, but I've been getting complaints that the web interfaces are sporadically down. I don't know exactly when this started as these services are rarely used, they're only for maintenance purposes.
I have confirmed that the issue exists – the router is sometimes inaccessible and VPN, web IF, etc are unusable, and it doesn't respond to ping either. However it does respond to SMS commands. If tends to work again after waiting it out.
At the moment I can not ping the router remotely, my requests just time out – but when I send an SMS message to get the router status I find that:
1) The router is connected to LTE
2) The WAN IP is the same that the DDNS domain resolves to
so I take it this is neither a mobile data issue nor a DDNS problem.
I just rebooted the router by SMS, and it rebooted successfully and was assigned a new WAN IP. When I try to ping the DDNS host name I can see that it now points to the new IP, so obviously that bit works – but it still does not respond to ping and is just as inaccessible as it was before.
I'm really puzzled, what could be causing this?