H12-821_V1.0 · Question #575
Which of the following BGP path attributes are optional transition attributes? (Multiple choice)
The correct answer is A. Aggregator C. Community. Aggregator (A) and Community (C) are optional transitive attributes - meaning BGP routers are not required to support them, but if they don't recognize them, they must still forward them to other BGP peers rather than drop them. MED (B) is optional non-transitive: it influences…
Question
Options
- AAggregator
- BMED
- CCommunity
- DCluster-List
How the community answered
(41 responses)- A73% (30)
- B10% (4)
- D17% (7)
Explanation
Aggregator (A) and Community (C) are optional transitive attributes - meaning BGP routers are not required to support them, but if they don't recognize them, they must still forward them to other BGP peers rather than drop them.
MED (B) is optional non-transitive: it influences path selection between ASes but is dropped at the AS boundary rather than passed along, so it cannot be transitive by definition. Cluster-List (D) is also optional non-transitive - it's used internally by route reflectors to prevent routing loops and is only meaningful within a single AS, so it must not propagate beyond it.
Memory tip: Think "A-C = Across Carry" - Aggregator and Community are the two optional attributes that get carried across to other peers even when unrecognized. MED and Cluster-List both have a local/boundary scope, which tells you they're non-transitive.
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