Which two BGP mechanisms are used to prevent routing loops when using a design with
redundant route reflectors? (Choose two.)
A.
Cluster-list
B.
AS-Path
C.
Originator ID
D.
Community
E.
Origin
Explanation:
http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.7/routing/configuration/guide/rc37bgp.html
As the iBGP learned routes are reflected, routing information may loop. The route reflector
model has the following mechanisms to avoid routing loops:
•Originator ID is an optional, nontransitive BGP attribute. It is a 4-byte attributed created by
a route reflector.
The attribute carries the router ID of the originator of the route in the local autonomous
system. Therefore, if a misconfiguration causes routing information to come back to the
originator, the information is ignored.
•Cluster-list is an optional, nontransitive BGP attribute. It is a sequence of cluster IDs that the
route has passed. When a route reflector reflects a route from its clients to nonclient peers,
and vice versa, it appends the local cluster ID to the cluster-list. If the cluster-list is empty, a
new cluster-list is created. Using this attribute, a route reflector can identify if routing
information is looped back to the same cluster due to misconfiguration. If the local cluster ID
is found in the cluster-list, the advertisement is ignored.