300-510 · Question #72
Which two BGP mechanisms are used to prevent routing loops when using a design with redundant route reflectors? (Choose two.)
The correct answer is A. Cluster-list C. Originator ID. Route reflectors use two dedicated attributes to prevent routing loops in IBGP topologies: (1) Cluster-list - each route reflector adds its Cluster ID to this attribute before reflecting a route. If an RR receives a route that already contains its own Cluster ID in the…
Question
Which two BGP mechanisms are used to prevent routing loops when using a design with redundant route reflectors? (Choose two.)
Options
- ACluster-list
- BAS-Path
- COriginator ID
- DCommunity
- EOrigin
How the community answered
(33 responses)- A94% (31)
- B3% (1)
- D3% (1)
Explanation
Route reflectors use two dedicated attributes to prevent routing loops in IBGP topologies: (1) Cluster-list - each route reflector adds its Cluster ID to this attribute before reflecting a route. If an RR receives a route that already contains its own Cluster ID in the cluster-list, it discards the update, preventing inter-cluster loops. (2) Originator ID - the first RR sets this attribute to the BGP Router-ID of the original client that advertised the route. If any router receives a route whose Originator ID matches its own Router-ID, it discards the update, preventing intra-cluster loops. AS-Path (B) and Origin (E) are used in standard EBGP loop prevention, not specific to route reflector redundancy. Community (D) is a policy attribute, not a loop-prevention mechanism.
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