BGP Attributes for Loop Prevention

AD.

In a BGP route reflector environment, loops can occur when a route is reflected back to the originator of the route, resulting in a routing loop. To prevent such loops, BGP uses the following two attributes:

1. Cluster ID: When a BGP route is received by a route reflector, the route reflector assigns a cluster ID to the route. The cluster ID is a 32-bit value that is used to uniquely identify a set of route reflectors that belong to the same cluster. When a route is reflected to a route reflector in the same cluster, the receiving route reflector checks the cluster ID of the route and discards the route if the cluster ID matches its own cluster ID. This prevents loops within the same cluster.

2. Originator ID: The originator ID is a BGP attribute that is used to identify the originator of a route in a BGP route reflector environment. The originator ID is set to the BGP router ID of the originator of the route. When a route is received by a route reflector, the route reflector sets the originator ID attribute to its own router ID before reflecting the route to other route reflectors. When a route is received by a route reflector that has the same router ID as the originator ID, the route is discarded. This prevents loops within the same router.

Therefore, the correct options are A. cluster ID and D. originator ID. The local preference, origin, and AS_PATH attributes do not prevent loops in a route reflector environment.