BigPond Authentication (aka BPA or heartbeat) is designed to stop more than one computer using BigPond at a time; and will block the service if it thinks you’re trying to login twice. Of course this isn’t realistic, which is why BPA is built into the Vigor 2100 and 2900 and the NAT hides your computers from BigPond.
However if your Vigor reboots or power is interrupted briefly it may try to log in without realising that BigPond’s server thinks that you are already logged on – and hence BigPond blocks your connection.
The work around is to wait until the BigPond Authentication Server times your connection out – 15 minutes – before turning your Vigor back on.
BigPond announced in Nov 2006 that they will be gradually migrating customers to a more conventional method (without BPA/heartbeat) … but have not given a timeframe for this.
Update: BigPond no longer use the BPA/heartbeat authentication system.