By definition, the BGP synchronization rule requires that when a BGP router receives information about a network from an I-BGP neighbor, it does not use this information until a matching route : static or dynamic : learned via an IGP (Interior Routing Protocol like OSPF, that uses the default routing table (vrf0 or GRT, Global routing table), exists in the default routing table.
Why is this helpful? to get control of the effective forwarding of packets based on the routing information received by BGP, for example, to prevent loops or blackholes: we make sure that routing information received by BGP is resolvable using the routing information in the local (default) routing and forwarding router tables to the next destination that is directly connected or multihop from the source…
Deep in… and network setup
Let’s deep into it and ask ourselves, what does it mean a “matching route” in this statement? Same prefix? Next-hop? Etc. What do you mean exactly by “does not use that information”? In global routing table? Advertising the route (information) to peers?
