S12. What problem is poison reverse solving and how? Flashcards
What is poison reverse?
Poison reverse is a technique used in routing protocols to solve the count-to-infinity problem
How does the count-to-infinity problem arise?
It arises in distance-vector routing algorithms when there are routing loops or link failures.
How do routing loops arise?
In distance-vector routing, routers exchange information with their neighbors, advertising the distance to reach each destination network. When a link fails or a routing change occurs, routers update their routing tables accordingly and propagate this information to their neighbors. If there is a loop of routers or if the routing updates take time to propagate through the network, it’s possible for routers to incorrectly learn that a failed route is still reachable, which leads to routing loops.
How does poison reverse address the issue of routing loops?
Poison Reverse addresses this issue by “poisoning” or invalidating routes through the failed link. When a router detects a link failure, it advertises an infinite metric for the affected routes back to the neighbor it learned the routes from.
How does route poisoning solve the issue of routing loops?
By poisoning the route with an unreachable metric, the router signals to its neighbors that the route is no longer valid, preventing them from inadvertently using it.
How does poison reverse accelerate the convergence of routing tables?
Becaues routers immediately learn about unreachable routes.
Does poison reverse completely eliminate the count-to-infinity problem?
While Poison Reverse does not completely eliminate the count-to-infinity problem, it significantly reduces its impact and helps maintain stable and efficient routing in distance-vector routing protocols.
What is the count-to-infinity problem?
In distance-vector routing algorithms, routers exchange information about network distances with their neighbors. When a router receives an update about a shorter route to a destination, it adds its own distance to the reported distance and sends it to its neighbors. If this process continues indefinitely, with each router incrementing the distance, it leads to the count-to-infinity problem.
