Core Issue
A valid route must exist in the routing table for Border Gateway Protocol (BGP) to advertise a classful network by issuing the network configuration command (under router BGP).
Resolution
To resolve this issue, ensure that a valid route exists in the routing table. The definition of a valid route depends on whether the auto-summary command is enabled under BGP.
For more information, refer to these documents:
show ip bgp {network mask}
Prefix/network does not exist
