Which three statements accurately describe default BGP advertisement rules?

The statement that IBGP peers advertise routes received from EBGP peers to other IBGP peers accurately reflects an important aspect of Border Gateway Protocol (BGP) behavior. In BGP configurations, the fundamental rule is that a route learned via EBGP (External BGP) can be shared by an IBGP (Internal BGP) peer with other IBGP peers. This is essential for maintaining routing consistency within an Autonomous System (AS) because it ensures that all IBGP routers have similar route information, which is crucial for efficient and loop-free routing decisions.

The operational mechanics behind this rule come from the need to have a full mesh of IBGP connections within an AS, ensuring that all routers can share and advertise reachable networks learned from external peers. Without this mechanism, some IBGP peers might remain unaware of routes presented by EBGP peers, leading to incomplete or inconsistent routing tables.

Thus, the summarization of BGP advertisement rules emphasizes the critical flow of BGP route information: EBGP to IBGP route propagation ensures that when any IBGP peer receives a route from an EBGP peer, it can propagate this information to maintain the integrity and effectiveness of routing across the internal topology of the AS.