Poisoned reverse prevents routing loops from forming. An update is sent back to the router that propagated the route to inform it that the network is unreachable at the associated interface.
However, this has a significant disadvantage over WAN connections: The central location transmits a high number of routes which would then suffer from route poisoning, so leading to a heavy load on the available bandwidth. For this reason, poisoned reverse can be manually activated for every LAN/WAN interface.
The LAN and WAN RIP tables have been extended for the configuration of poisoned reverse.