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A routing metric is a unit calculated by a routing algorithm for selecting or rejecting a routing path for transferring data/traffic.
A routing metric is calculated by routing algorithms when determining the optimal route for sending network traffic. Metrics are assigned to each different route available in the routing table and are calculated using many different techniques and methods based on the routing algorithms in use. Some of the parameters used for calculating a routing metric are as follows:
Routers are the core networking devices used to transport data over different interconnected networks. An autonomous system or a large enterprise network may contain many different networks, along with many routers working to enable communications among them. Similarly, a segment of a large network may contain many small networks. Thus, there are many network communication paths involved in transporting network traffic. As these small and large networks are interconnected, and a network router records several paths or routes leading up to any specific node or network. However, to decide upon the optimal path among them, a router uses a routing metric as a core selection process.
Routing metrics are composed of several different parameters and operational environments to determine points for comparisons among the available paths. Generally, routing metrics are also known as the cost calculation for a given path, which varies depending on the routing protocol in use. For example, distance vector routing rotocols implement the Bellman-Ford algorithm to add the total number of hops, or intermediary routers, involved in reaching a destination. Path reliability, load, speed, latency, packet loss and a few other factors are inputs for calculating path cost in modern routing protocols.