Core Issue
The most common reason an internal Border Gateway Protocol (iBGP) route is not advertised is enabled synchronization. The outbound filter policies can also prevent the BGP from sending updates.
Resolution
To resolve this issue, perform these steps:
- Ensure that synchronization is not enabled by issuing the no synchronization command under the BGP configuration.
- Ensure that you do not have any outbound filter policies, which may prevent BGP from advertising the networks in question.
For more information on synchronization, refer to these documents:
show ip bgp {network mask}
Prefix / network exists, learned by iBGP NOT marked received only
