Unifi USG-3 vs ISP (PPPoE): I can ping the ISP's network, but not outside of it

in flag

Our network is based on Ubiquiti Unifi devices and has some printers and assorted clients, and a Synology NAS running DSM7.

A few days ago the network suddenly developed problems, although I have made zero changes to any of the network devices these past two weeks. It's beginning to become a critical issue, but I'm stumped.

It's not a large network:

  • Fiber connection enters the premises
  • Fiber/ethernet media converter (zero configuration options, and owned by ISP)
  • Ubiqiti USG ("Unifi Security Gateway")
  • Ubiqiti Unifi Switch
  • Ubiqiti Unifi access points
  • misc. clients, printers, ...
  • Synology NAS (the Unifi controller is running in a Docker container, along with other server tasks)

Of note is that the USG has a PPPoE configuration (username, password, VLAN) that must match what is provided by the ISP. This has been working fine "since forever". However, a few days ago the internet connection just ... dropped. From talking with the ISP tech support, their connection up to the USG checks out, and from what I can tell via Unifi our network also checks out. And yet, no connection.

Or is there?

It turns out that I can actually ping the ISP's default gateway (, and I can also ping other addresses on the ISP's network (variations on our own public IP; variations on their gateway IP) but I cannot ping anything outside of the ISP's network (eg., -- heck, not even their own preferred DNS servers (eg.!

Because they say that there is a connection into our premises, the problem must be on our end. I have been unable to obtain any explanation as to why I am able to access only their network but nothing outside.

To me this suggests that the ISP must have made some change that has affected our connection.

What gives? How can I troubleshoot this?

It may be related to my other issue, that the NAS (also serving as a Unifi controller) has been giving me grief with logging into it. I do not suspect a malicious attack, for whatever that's worth.

Edit 2: Now that I've received their official equipment, I see the exact same behaviour. At least they're now willing to sic their network team on the issue, so there is hope it will be resolved within the week.

Edit 1: I can't check the routing table as the interface of the USG in stand-alone mode is very simplistic: main screen configuration screen

vidarlo avatar
ar flag
Check the routing table of your USG.
Noughtnaut avatar
in flag
@vidarlo I've reset the USG so it's in stand-alone mode where there are hardly any options to configure, only PPPoE credentials and LAN DHCP range.
in flag
In your first image, you didn't add any DNS server addresses.
Noughtnaut avatar
in flag
@TorbenGundtofte-Bruun I did, but either they don't "stick" or they're simply not shown.
vidarlo avatar
ar flag
Well, what does your routing table look like?
Nikita Kipriyanov avatar
za flag
Can you try to temporary set up the Internet connection on ISP-recommended hardware and check if it works? Then, when *that* works, repeat configuring your USG.
Noughtnaut avatar
in flag
Yeah, that's precisely what I'm going to do. My ISP "naturally" don't have any wifi routers in the country, so one is being shipped to me.
Noughtnaut avatar
in flag
Now that I've received their official equipment, I see the exact same behaviour.
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