BGP does not allow a route to be advertised unless it is the best path in the RIB and an export policy allows the advertisement.
In some cases, it may be useful to advertise the best BGP path to peers despite the fact that is inactive. For example, because there are one or more preferred non-BGP routes to the same destination and one of these other routes is the active route. One way SR OS supports this flexibility is using the advertise-inactive command; other methods include best-external and add-paths.
When the BGP advertise-inactive command is configured so that it applies to a BGP session it has the following effect on the IPv4, IPv6, mcast-ipv4, mcast-ipv6, label-IPv4 and label-IPv6 routes advertised to that peer.
If the active route for the IP prefix is a BGP route then that route is advertised.If the active route for the IP prefix is a non-BGP route and there is at least one valid but inactive BGP route for the same destination then the best of the inactive and valid BGP routes is advertised unless the non-BGP active route is matched and accepted by an export policy applied to the session.
If the active route for the IP prefix is a non-BGP route and there are no (valid) BGP routes for the same destination then no route is advertised for the prefix unless the non-BGP active route is matched and accepted by an export policy applied to the session.