Answer: The cause of the routing loop is the inconsistency of routing information among routers that use distance vector routing protocols. The poison reverse method is a way to solve it by advertising unreachable routes with an infinite metric.
Explanation: A routing loop is a situation where a packet is forwarded endlessly among routers without reaching its destination. Routing loops can cause network congestion, packet loss, and increased latency. Routing loops can occur when routers use distance vector routing protocols, such as RIP or EIGRP, which exchange routing information based on the distance (or cost) to each destination network.
The cause of the routing loop is the inconsistency of routing information among routers that use distance vector routing protocols. This can happen when a link or a network goes down, and the routers do not update their routing tables immediately. Instead, they rely on periodic updates from their neighbors, which may take some time to propagate through the network. During this time, some routers may have stale or incorrect information about the best path to a destination network, and may forward packets to a neighbor that does not have a valid route. This neighbor may then forward the packet back to the original router, creating a loop.
The poison reverse method is a way to solve the routing loop problem by advertising unreachable routes with an infinite metric. This means that when a router detects that a link or a network is down, it does not simply remove the route from its routing table. Instead, it sends an update to its neighbors with a metric that indicates that the route is unreachable (such as 16 for RIP or 4,294,967,295 for EIGRP). When the neighbors receive this update, they update their routing tables accordingly and stop forwarding packets to the failed route. This way, the poison reverse method prevents routers from using invalid routes and creating loops.
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