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Router metrics are metrics used by a router to make routing decisions. It is typically one of many fields in a routing table. Metrics are used to determine whether one route should be chosen over another. The routing table stores possible routes, while link-state or topological databases may store all other information as well. For example, Routing Information Protocol uses hopcount (number of hops) to determine the best possible route. The route will go in the direction of the gateway with the lowest metric. The direction with the lowest metric can be a default gateway. Router metrics can contain any number of values that help the router determine the best route among multiple routes to a destination. A router metric typically based on information like path length, bandwidth, load, hop count, path cost, delay, Maximum Transmission Unit (MTU), reliability and communications cost. ==Examples== A Metric can include: * measuring link utilisation (using SNMP) * number of hops (hop count) * speed of the path * packet loss (router congestion/conditions) * latency (delay) * path reliability * path bandwidth * throughput (- query routers ) * load * MTU In EIGRP, metrics is represented by an integer from 0 to 4,294,967,295 (The size of a 32-bit integer). In Microsoft Windows XP routing it ranges from 1 to 9999. A Metric can be considered as:〔S. D. Rao, C. S. R. Murthy: “Distributed dynamic QoS-aware routing in WDM optical networks”, Computer Networks, Volume 48, Issue 4, 15 July 2005, Pages 585-604〕 * additive - the total cost of a path is the sum of the costs of individual links along the path, * concave - the total cost of a path is the minimum of the costs of individual links along the path, * multiplicative - the total cost of a path is the product of the costs of individual links along the path. A survey of routing metrics can be found (here ). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Metrics (networking)」の詳細全文を読む スポンサード リンク
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