Telstra is slowly bringing its NBN and ADSL customers back onto its network after as much as four days offline for some of its users following a Friday fault.
Early on Friday morning reports began flooding in from Telstra broadband users across the country about an inability to access their services.
The telco confirmed the issue at the time and said it was working to identify the problem.
However it took the company some time to discover the cause of the outage, meaning Telstra did not identify the fault until late on Friday. The issue affected around 375,000 customers at its peak, it is understood.
"In this case the complexity of the issue meant it took some time to identify and it impacted customers in different ways at different times, depending on the type of modem that individual customers had and the environment that it was operating in," Telstra chief operating officer Kate McKenzie said in a statement.
"This made the fix on this occasion longer and more difficult."
A fault had occured with the device that manages the interaction between Telstra's network and customer modems, Telsra said. It has been contacted for further detail.
Telstra was able to apply a fix to the problem but "residual issues" over the weekend prevented a number of customers from reconnecting to the network, Telstra said.
It meant the telco was continuing to bring broadband customers back online on Monday, four days after the problems first appeared.
Customers complained their modems were stuck in an endless loop of turning on and connecting before turning off and starting again.
Telstra advised those affected to restart their modems and to contact the telco should a restart be unsuccessful.
“We apologise to our customers for the impact this has had on their services," a spokesperson said.
The issue of reconnecting customers after an outage was also a problem in the telco's mobile network outages earlier this year, where the mass re-registration of devices overloaded the database that registers customer devices.
The latest outage is the fourth major network problem for Telstra this year. The three earlier outages - to the mobile network - forced Telstra to pledge $50 million to improve its network.
The telco has also been rocked by a series of smaller network problems, including to NBN services in NSW and to its domain name servers, while a third-party routing issue in March locked Telstra customers out of Amazon Web Services' Sydney data centre.