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BGP does not advertise the network until IGP has propagated the route within the AS

Core Issue

If an Autonomous System (AS) passes traffic from another AS to a third AS, then the Border Gateway Protocol (BGP) will not advertise a route before all the routers in the AS have learned about the route through the Interior Gateway Protocol (IGP).

Resolution

To allow a BGP router to put a network in its routing table and advertise it (even if it does not have an IGP path to that network), issue the no synchronization command.

For information on synchronization, refer to the Synchronization section of BGP Case Studies.

For information on the BGP route advertisement, refer to the Troubleshooting BGP Route Advertisement section of Troubleshooting BGP.

BGP Prefix Origination Method

Via redistribution


Type of Route Missing from Routing Table

All routes / All routes from specific neighbor

Valid Route to BGP Next Hop

Valid route to next hop exists

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