Why ibgp does not propagate route leaned from one ibgp neighbor to another ibgp neighbor in same autonomous system?

• Check the synchronization because the default behaviour is off.
• should be full mesh

its a bgp loop avoidance mechanism within the single Autonomous system because in ebgp as-path sequence is used as loop avoiding method but within a single AS as-path is not updated as routes are propagated within the AS. So to control the loop in ibgp no ibgp neighbor gives ibgp route to its ibgp peer. Route-reflectors or ibgp fullmesh are the methods for route propagation within the single bgp AS 

Because of a rule in Ibgp called as Split horizon so to avoid loops in the AS.So to make communication either you make a full mesh using neighbor commands or you can use route reflectors.

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In Order to avoid loop in BGP.            

In order to avoid loops.                                                                             When  a route learned from the same autonomous system, remote router in the ibgp thinks that it is its own route so the route did not propagate.

In order to avoid Loops.

This is because of the Split Horizon in BGP which used to prevent loops

You should check the TTL Security hops and the interface that is propagating/advertising is mentioned or not. for far end and local end. 

ibgp will not propagate those routs, until he learn them from internal protocol, like OSPF or Rip