Customers of TPG and its subsidiary brands suffered a two-hour outage of internet and voice services nationwide.
The problems started at around 12.30pm AEDT and were resolved at 2.30pm.
TPG said in a brief advisory that the “unplanned” outage caused “NBN, ADSL, TPG FTTB internet and home phone connection difficulties”.
It said IT and technical teams had investigated the issues "as a priority" and apologised to users "for the inconvenience".
Subsidiary brand iiNet suggested the root cause is a domain name system (DNS) fault.
“As a workaround, using an alternate publicly available DNS may assist in restoring connectivity to the internet and VOIP for customers,” it said.
Users of the Whirlpool broadband forum also reported that changing the DNS settings of their modem - where possible - was resolving the connectivity issues.