Generally most of routers like cisco and junos allow a router to have dual-As to be configured via a "local-as" command which overrides the global as-number configured in "router bgp ". Also local-as prepending may or may not happen based on configurations; for example "no-prepend" in cisco. Now my question is, is there any RFC which which standardises this Dual-As support?? Which provides guidelines on whether or not to prepend the "local-as" to As-Path attributes in the Bgp updates ?