Cause of massive Optus outage revealed

Optus has revealed the cause of an outage that crippled the nation last week, citing changes to 'routing information' following a software upgrade.

The meltdown affected up to 10 million Australians and over 400,000 business who were left in the dark for up to 12 hours after their internet and phone services were cut off. 

Optus told its disgruntled customers on Monday afternoon it had been trying to discover what went wrong and insisted they had 'taken steps to ensure it will not happen again'.

'We apologise sincerely for letting our customers down and the inconvenience it caused,' the statement said.

'At around 4.05am Wednesday morning, the Optus network received changes to routing information from an international peering network following a routine software upgrade,' the statement added. 

'These routing information changes propagated through multiple layers in our network and exceeded preset safety levels on key routers which could not handle these.'

The statement said the action resulted in routers disconnecting from the Optus IP Core network to protect themselves.

This resulted in a large scale effort to reconnect or reboot the routers physically, requiring 'the dispatch of people across a number of sites in Australia'.

More to come.