RIP uses a hop count metric. An unreachable network is indicated by setting the hop count to 16, which RIP interprets as an infinite distance.
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RIP sends periodic updates every 30 seconds minus a small random variable to prevent the updates of neighboring routers from becoming synchronized.
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A route entry is marked as unreachable if six updates are missed.
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The garbage collection timer, or flush timer, is set when a route is declared unreachable. When the timer expires , the route is flushed from the route table. This process allows an unreachable route to remain in the routing table long enough for neighbors to be notified of its status.
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The random timer, whose range is 1 to 5 seconds, prevents a " storm " of triggered updates during a topology change.
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A Request message asks a router for an update. A Response message is an update.
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A Request message may either ask for a full update or in some special cases it may ask for specific routes.
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A Response is sent when the update timer expires, or upon reception of a Request message.
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RIP updates do not include the subnet mask of the destination address, so a RIP router depends on the subnet masks of its own interfaces to determine how an attached major network address is subnetted. If a router does not have an attachment to a particular major network address, it has no way to know how that major network is subnetted . Therefore, no subnets of a major network address can be advertised into another major network.