Long story short we were having intermittent connection issues since day 1 but whenever we got close to breaking point the connection started working well for a while so we stuck around but this week my partner (WFH) finally had enough after wasting time on the phone with tech support. We are using a HFC NBN connection and the NTD always shows "online", the DS244WTV modem has all the right lights on and restarting both does get us connected sometimes but not this time. I started digging through the gateway page 192.168.1.1 (user:admin pw:support180) and found tools->ping.
I tried both primary (172.30.30.10) and secondary (172.30.30.11) DNS who were set automatically at first installation and both failed. I then tried Google DNS (18.104.22.168) and OpenDNS (22.214.171.124) and pinging them was successful. Now I feel like an idiot because a Google search shows forum entries showing that people were having Southern Phone DNS server issues for years and this problem seems to persist.
The workaround on the DS244WTV:
BasicSetup->WAN Service, tick IPv4 Static DNS, add 2 open DNS servers e.g. Google at 126.96.36.199 or 188.8.131.52
As soon as I saved the new settings we were back online immediately. Turns out we had internet all the time we just couldn't reach the 2 DNS servers to translate the requested address.
I'm posting this in the hope that this workaround might help someone who experiences intermittent connection issues when all the lights on the NTD and modem suggest that nothing is wrong.
Solved Go to Answer
I found the same a number of times - I though service was out, but it was just no response from the ISP provided DNS servers (my router is setup to use the Southern Phone DNS servers). I swapped out to the Cloud Flare public DNS (184.108.40.206) and it worked again.
I've found that if I set the router to use one of the ISP provided DNS servers and one public DNS server, I tend to get less issues - when the ISP DNS servers don't respond, it fails over to public DNS.