This deprecated setting enables or disables RIP poison reverse on a specific interface, a loop-prevention technique where a router advertises a route back toward the neighbor it learned it from, but with an infinite metric, to explicitly signal not to use it to reach that route. When poison reverse is turned off, the router falls back to plain split-horizon instead, simply not re-advertising the route back toward that neighbor at all. For example, disabling this on a slow WAN link could reduce the size of RIP updates sent over that link, at the cost of slightly slower loop detection compared to poison reverse.