At 1:34pm we received alerts regarding some destinations being unreachable.
Further investigation showed that our fibre link to Level3 was down unexpectedly. This caused a BGP routing event.
Our configuration started the BGP reconvergance process as soon as the router saw the fibre link drop and outbound traffic was re-routed via other paths.
Other routers on the internet would take around 3-4 minutes to re-learn the alternate paths for inbound. This is out of our control.
This only affected paths via Level3 and not via our other connectivity partners and as such would appear as a partial outage.
We have contacted Level3 and raised a ticket to investigate. Our network is fully operational via alternate connectivity.