Default policies: BGP accepts and advertises active BGP routes; OSPF import accepts all and export rejects all; RIP export rejects all

Every routing protocol in Junos has a built-in default policy. It is applied automatically at the end of any policy chain, so it decides what happens to a route that none of your configured policies explicitly accepts or rejects. If you do not configure any policy at all, the default policy is all that applies. Knowing each protocol's default explains a lot of behavior that surprises beginners.