BGP Path Filtering

[rm2017]

I'm trying to filter a backup default route from being advertised to an eBGP neighbor. Under normal operations, Router A advertises a default route to Router C. Router A receives a backup default route from Router B via eBGP. Router C receives a default route from A and a backup default route from B - both via eBGP. I am trying to prevent the backup default route from being advertised from A->C during a failover. Can I use AS Path Filtering to filter the following path:

[100 200 ?]

or can I not match the ? in the as-path?

[olorunloba]

I will advice that you use BGP communities. You could tag the default route that you do not want exported with the well known community no-export.