http://www.rfc-editor.org/rfc/rfc8212.txt
RFC 8212: Default External BGP (EBGP) Route Propagation Behavior without Policies, J. Mauch, J. Snijders, G. Hankins2017-07-01T23:00:00-00:00This document updates RFC 4271 by defining the default behavior of a BGP speaker when there is no Import or Export Policy associated with an External BGP session.