Core Issue
A Border Gateway Protocol (BGP) router with synchronization enabled will not install an internal Border Gateway Protocol (iBGP) learned route into its routing table if it cannot validate those routes in its Interior Gateway Protocol (IGP) routing table.
Resolution
To resolve this issue, turn off synchronization by issuing the no synchronization configuration command under the router BGP configuration.
For additional information, refer to the Unable to Announce iBGP-Learned Routes section of Troubleshooting When BGP Routes Are Not Advertised.
Valid Route to BGP Next Hop
Valid route to next hop exists
show ip bgp {network mask}
Prefix / network exists, learned by iBGP NOT marked received only
