A BGP conditional advertisement allows you to control which route to advertise in the event that a preferred route is not available in the local BGP routing table (LocRIB), indicating a peering or reachability failure. This is useful where you want to try to force routes to one AS over another, such as when you have links to the internet through multiple ISPs and you want traffic to be routed to one provider instead of the other except when there is a loss of connectivity to the preferred provider.

For conditional advertisement, you configure a Non Exist filter that specifies the preferred route(s) (Address Prefix) plus any other attributes that identify the preferred route (such as AS Path Regular Expression). If a route matching the Non Exist filter is not found in the local BGP routing table, only then will the firewall allow advertisement of the alternate route (the route to the other, non-preferred provider) as specified in its Advertise filter.

To configure conditional advertisement, select the Conditional Adv tab, Add a conditional advertisement, and configure the values described in the following table.