Advertising Inactive Routes

Under normal circumstances, routes that are not being used to forward traffic—inactive routes—are not advertised to peers unless synchronization is enabled. For example, suppose a BGP speaker receives a route to a particular prefix, determines that it is the best route to the prefix, and stores the route in the IP routing table (sometimes known as the forwarding information base, or FIB). This route might not be used for forwarding to that prefix; for example, if you have configured a static route to the same destination prefix. Because static routes have better administrative distances than BGP received routes, IP will use the static route rather than the BGP received route for forwarding traffic to that prefix. The BGP received route is inactive and is not advertised to peers. You can use the bgp advertise-inactive command to enable the advertisement of inactive received routes.

bgp advertise-inactive

• Use to enable the BGP speaker to advertise inactive routes—best routes in the IP forwarding table that are not being used to forward traffic. This feature is disabled by default.
• Issuing this command does not affect the BGP rules for best route selection, or how BGP populates the IP forwarding table.
• Example

  host1(config-router)#bgp advertise-inactive

• The new value is applied to all routes that are subsequently placed in the IP routing table.

  To apply the new value to routes that are already present in the IP routing table, you must use the clear ip bgp * command (this command will bounce the BGP sessions).

• Use the no version to prevent the advertising of received BGP routes unless one or both of the following are true:
  • The received route is in the BGP forwarding table and is being used to forward traffic (the route is active).
  • Synchronization is enabled.
• See bgp advertise-inactive.

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