CCNA distance-vector routing interview questions test your understanding of route selection, hop count, loop prevention, filtering, authentication, and load balancing. The concise explanations below correct common misconceptions and connect each answer to practical verification.
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How does a distance-vector protocol choose a path?
A distance-vector protocol evaluates routes using its configured metric. RIP uses hop count, so it selects the route with the fewest router hops. Other distance-vector technologies may calculate metrics differently.
Which algorithm is associated with distance-vector routing?
Distance-vector routing is based on the Bellman-Ford algorithm. Routers learn the distance and direction to networks from neighboring routers rather than maintaining a complete topology map.
What is hop count?
Hop count measures how many routers a packet must cross to reach a destination. RIP accepts routes with metrics from 1 through 15; a metric of 16 means unreachable.
What is route filtering?
Route filtering controls which routes a router accepts or advertises. It can reduce unnecessary routing information, enforce policy, or prevent selected prefixes from being learned by another routing process or neighbor.
What is load balancing?
Load balancing allows traffic to use more than one valid path. RIP supports equal-cost load balancing when multiple routes have the same metric. The number of installed paths depends on platform and routing configuration.
What is a classful protocol?
A classful routing protocol does not advertise subnet-mask information. RIPv1 is classful. RIPv2 carries subnet masks and supports VLSM and CIDR, making it classless.
How many hops can RIP advertise?
RIP supports a maximum usable path of 15 hops. Any destination advertised with a metric of 16 is treated as unreachable.
What is a triggered update?
A triggered update is sent soon after a significant routing change rather than waiting for the regular periodic timer. It helps neighboring routers learn that a route changed or became unavailable.
Which protocols send periodic updates?
Traditional distance-vector protocols such as RIP periodically advertise routing information. RIP normally sends its complete routing table every 30 seconds, although triggered updates can occur between intervals.
How do distance-vector protocols prevent loops?
Common mechanisms include split horizon, route poisoning, poison reverse, triggered updates, and hold-down behavior. These techniques reduce the risk of routers repeatedly advertising an invalid path to one another.
What is split horizon?
Split horizon prevents a router from advertising a route back through the interface on which that route was learned. This rule helps stop two-router routing loops.
What is route poisoning?
Route poisoning advertises a failed route with an infinite metric. In RIP, the poisoned metric is 16, informing neighbors that the destination is no longer reachable.
What is the difference between plaintext and MD5 authentication?
Plaintext authentication exposes the configured key within the routing packet, while MD5 uses a cryptographic digest to verify the update. MD5 is the more secure option when supported and correctly configured.
Which commands verify distance-vector routing?
Use show ip protocols to review timers and network statements, show ip route to inspect installed routes, and show ip rip database for RIP-learned information. Interface status and access-control policies should also be checked.
How should you answer routing interview questions?
Start with the definition, identify the metric, explain the control-plane behavior, and name a verification command. This approach demonstrates practical understanding instead of simple memorization.
Practice with Updated Questions and Answers
Use these notes for concept review, then work through the Cisco 200-301 Premium PDF for additional structured question-and-answer practice.