Understanding IBGP and EBGP Interaction

ACE

IBGP (Internal Border Gateway Protocol) and EBGP (External Border Gateway Protocol) are two routing protocols that are used to exchange routing information between routers in different autonomous systems (ASes) or within the same AS. Here are the correct statements about their interaction:

A. IBGP is used within an AS, whereas EBGP is used between two different ASs. This statement is true. IBGP is used to distribute routing information within an autonomous system, while EBGP is used to exchange routing information between different autonomous systems.

B. EBGP peering is normally loopback-based to provide tolerance for interface or link failures. This statement is partially true. EBGP peering can be based on loopback addresses, but it is not the only option. EBGP can also use physical interfaces or IP addresses assigned to those interfaces. Loopback-based peering is often used to provide high availability and redundancy because loopback interfaces are less prone to failures.

C. By default, EBGP updates the next-hop attribute, whereas IBGP does not. This statement is true. EBGP updates the next-hop attribute of the routes it advertises, while IBGP does not. This is because EBGP assumes that the next-hop is reachable by the receiving router, while IBGP assumes that the next-hop is within the same autonomous system and reachable through an IBGP session.

D. IBGP speakers can re-advertise IBGP-learned or EBGP-learned routes to other IBGP speakers. This statement is true. IBGP speakers can advertise routes learned from other IBGP speakers or EBGP peers to other IBGP speakers within the same autonomous system. This is known as route reflection and it helps to reduce the number of IBGP sessions required in large autonomous systems.

E. EBGP speakers can re-advertise IBGP-learned or EBGP-learned routes to other EBGP speakers. This statement is false. EBGP speakers cannot advertise routes learned from other EBGP speakers or IBGP speakers to other EBGP speakers. This is because EBGP does not propagate routes learned from other EBGP peers to other EBGP peers, unless explicitly configured to do so.

In summary, IBGP and EBGP are both important routing protocols that are used to exchange routing information between routers in different autonomous systems or within the same autonomous system. Understanding their interaction is crucial for designing and troubleshooting complex networks.