Reading through the documentation it looks like this emulates the legacy IOS model of announcing all BGP routes to neighbors by default unless there is a policy

Reading through the documentation it looks like this emulates the legacy IOS model of announcing all BGP routes to neighbors by default unless there is a policy configured. This outdated model has caused countless route leaks over the years. Any new or updated BGP implementations should require an explicit allow policy for any route advertisement to take place (at least to eBGP neighbors). IOS-XR and JunOS require explicit policies. This is covered in RFC8212: https://datatracker.ietf.org/doc/html/rfc8212 https://datatracker.ietf.org/doc/html/rfc8212