Cisco CCNA mock exam questions sample test – Question 76

.Which of the following statements describes split horizon?

A. The router learns from its neighbor that a route has gone down, and the router sends an update back to the neighbor with an infinite metric to that route.
B. For a period of time, the router will ignore any route advertisements with a lower metric to a downed route.
C. A router will not send route information back out the same interface over which it was learned.
D. The moment a router determines a route has gone down, it will immediately send a route update with an infinite metric to that route.
E. The packets are flooded when a topology change occurs, causing network routers to update their topological databases and recalculate routes.

Correct Answer: C

Explanation:
Split horizon is used to prevent routing loops in distance vector routing environments. It prevents a router from advertising a network back in the direction of the router from which it
was learned. In this sense, route advertisements flow “downstream” (away from the route), but never “upstream” (back towards the advertised route).
Poison reverse describes when a router learns that a network has gone down, and the router sends an update back to the neighbor with an infinite metric.
Holddown describes when a router ignores any route advertisements that have a lower metric to a downed route.
Triggered updates describe when a router immediately sends a route update with an infinite metric, as opposed to waiting for its next regularly scheduled routing update.
Link State Advertisements (LSA) are packets that are flooded when a topology change occurs, causing network routers to update their topological databases and recalculate routes.
Objective:
Routing Fundamentals
Sub-Objective:
Compare and contrast distance vector and link-state routing protocols
References:
Cisco > Articles > Network Technology > General Networking > Dynamic Routing Protocols