Which two statements about BGP facilitate the prevention of routing loops between two autonomous systems?

BGP (Border Gateway Protocol) is a protocol designed to exchange routing and reachability information among autonomous systems (AS) on the internet1.

Option A is correct. When an EBGP router advertises routes to its neighbors, it appends its AS number to the AS_PATH attribute1. This is a key mechanism in BGP to prevent routing loops1.

Option C is correct. BGP has a built-in loop prevention mechanism whereby if a BGP router detects its own AS in the AS_PATH attribute, it will drop the prefix and will not continue to advertise it2. This helps to prevent routing loops2.

Option B is incorrect. EBGP routers do not accept routes that contain their own AS number in the AS_PATH2. Instead, they drop such routes as part of the loop prevention mechanism2.

Option D is incorrect. While it’s true that EBGP routers append their AS number when advertising routes, they do not prepend their AS number1. The term “prepend” in BGP usually refers to a technique used to influence path selection by artificially lengthening the AS_PATH3.