BGP route advertisement rules
The current BGP implementation supports the following route advertisement rules:
When multiple feasible routes to a destination exist, the BGP speaker advertises only the best route to its peers.
A BGP speaker advertises only routes used by itself.
A BGP speaker advertises routes learned from an eBGP peer to all its peers, both eBGP and iBGP.
A BGP speaker does not advertise routes learnt from an iBGP peer to its other iBGP peers.
A BGP speaker advertises routes learnt from iBGP to eBGP peers. Note that BGP and IGP synchronization is disabled always and those routes are advertised to eBGP peers directly.