Which routing protocol uses successor and feasible successor?
Short answer
D EIGRP
Question
Key Takeaways
The question tests recognition of EIGRP-specific Diffusing Update Algorithm terminology, with the trap being to confuse EIGRP with OSPF or IS-IS.
EIGRP is the routing protocol that uniquely uses successor and feasible successor terms for loop-free path selection. Community consensus confirms D as correct for the N10-009 exam.
Common mistake: Choosing OSPF is a common mistake because OSPF is a well-known link-state protocol, but it uses SPF trees and LSA types, not successor/feasible successor.
Expert Analysis
Why the Answer Is Correct
EIGRP, a Cisco-proprietary hybrid protocol, uses the terms successor and feasible successor within its DUAL algorithm. A successor is the primary route with the best metric, while a feasible successor is a backup route that meets feasibility conditions, ensuring loop-free failover. This unique terminology is not used by IS-IS, OSPF, or BGP.
Why the Other Options Are Wrong
IS-IS and OSPF are link-state protocols that build a complete topology database and calculate shortest paths using Dijkstra; they do not maintain successor/feasible successor relationships. BGP is a path-vector protocol that selects best paths and may use multipath, but it does not use feasible successors. Only EIGRP has these specific DUAL concepts.
Community Comment Notes
Comment [1] correctly explains that EIGRP uses successor and feasible successor in DUAL to ensure efficient, loop-free path selection. Comment [2] adds that EIGRP is a hybrid distance-vector/link-state protocol. Comment [3] reinforces that the successor is the active route and the feasible successor is the backup route. All community votes were for D, aligning with the correct answer.
Official Reference
- https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/16406-eigrp-toc.html
- https://datatracker.ietf.org/doc/rfc7868/
These links open the official vendor documentation in a new tab.
Exam Strategy
Memorize protocol-specific buzzwords: EIGRP = DUAL, successor, feasible successor; OSPF = LSA, DR/BDR, SPF; IS-IS = TLV, DIS; BGP = AS-path, path attributes. When you see unique terms like these, identify the protocol first, then verify its characteristics.
Community Votes
100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 3 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 3
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TreyPar3 👍 3The routing technology that uses the concepts of a successor and a feasible successor is Enhanced Interior Gateway Routing Protocol (EIGRP). EIGRP is a Cisco-proprietary routing protocol that uses these terms in its Dual (Diffusing Update Algorithm) to ensure efficient and loop-free path selection.
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HeatSquad77 👍 2 Answered DD. Enhanced Interior Gateway Routing Protocol (EIGRP) Cisco’s proprietary hybrid protocol that has elements of both distance vector and link state routing.
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LadyBirdArchitect 👍 1 Answered DD. EIGRP In EIGRP, a successor is a primary route to a destination network, chosen based on having the best metric. The successor route is actively used to forward traffic to the destination network. If the successor becomes unavailable, EIGRP uses a backup route called a feasible successor.
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