Which of the following describes split horizon in RIP?

Split horizon is a technique used in distance-vector routing protocols like the Routing Information Protocol (RIP) to prevent routing loops and improve the efficiency of routing updates. The correct description of split horizon states that routes learned from a neighbor cannot be sent back to that same neighbor. This means that if a router receives a route advertisement from a neighbor, it will not share that route back to the neighbor from which it learned it.

This mechanism helps to avoid circular routing paths that would otherwise lead to an infinite loop. For example, if Router A learns about a route to a certain destination from Router B, it won't inform Router B about that route again, thus preventing Router B from thinking it can reach that destination via Router A.

The other descriptions provided refer to different aspects of routing behavior in RIP or other routing protocols. The idea of sending all routes after a fixed interval pertains to standard update intervals, which is not specific to split horizon. "Only the best route is sent to neighbors" refers to route selection practices, and "updates sent periodically regardless of link status" describes a different characteristic of RIP but does not relate directly to how split horizon operates.