BGP Synchronization rule:
Applicable to the following situations
1.When the AS is a transit AS,
2.When atleast one of the router in the AS is not running BGP
3.All the routers are running bgp but, they are not fully meshed or there is no RR.
When a BGP router learns about a network from an eBGP peer it advertises to other iBGP peers only after verifying that the network information is already available in the IGP.
BGP Split Horizon Rule:An iBGP router never advertises a route learned from its neighbour to any other iBGP peer. ( Conventional split horizon says that a route/network learned through an interface will never be advertised back on that interface)
One doubt: Suppose a Service Provider(SP) network. If all the internal routers are capable of running BGP(ibgp) and if a RR is there what is the need for running an IGP in the network?? Ans: For each of the RR clients to reach the RR, the IGP is required. Also the route to each networks between the routers also are propogated by the IGP.
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