A spokesperson confirmed on Monday that the cause of the outage was changes to routing information from an international peering network after a routine software upgrade at 4.05am on Wednesday.
“These routing information changes propagated through multiple layers in our network and exceeded preset safety levels on key routers which could not handle these. This resulted in those routers disconnecting from the Optus IP Core network to protect themselves,” a spokesperson said.
“The restoration required a large-scale effort of the team and in some cases required Optus to reconnect or reboot routers physically, requiring the dispatch of people across a number of sites in Australia. This is why restoration was progressive over the afternoon.”
There's a meme about how it's always 'one of you three' that came immediately to mind...
Mark.