In computer networking, the term "metric" refers to a value used by routing protocols to determine the best path to a destination network. Each routing protocol has its own way of calculating this metric, and it typically takes into calculation factors on some parameters like bandwidth, delay, reliability, load, MTU, path cost, hop counts and other attributes.
Here are some examples of how metrics are used in different routing protocols:
Routing Information Protocol (RIP): Routing Information Protocol (RIP): RIP uses hop count as its metric. Hop count is simply the number of routers a packet must traverse to reach the destination network. RIP supports a maximum of 15 hops, after that is considered as unreachable. If the same destination route comes to a router from different hop counts, RIP will learn the route with a lower hop count.
Open Shortest Path First (OSPF): OSPF calculates its metric based on the cost of the path to the destination network. The cost is derived from the bandwidth of the links along the path. OSPF prefers routes with lower path costs.
Enhanced Interior Gateway Routing Protocol (EIGRP): EIGRP uses multiple factors to calculate the metric for a path. Metric calculation uses bandwidth and delay by default but can include interface load and reliability, too of the path to the destination network. EIGRP routers calculate this metric using a formula and exchange this metric with neighboring routers to determine the best paths.
metric = [ K1 * bandwidth + (K2 * bandwidth)/256 - load) + K3 * delay] * [ K5/ (reliability + K4)]
Border Gateway Protocol (BGP): BGP uses various attributes to determine the best path to a destination network, such as ASN path length, origin type, and various optional attributes like local preference and MED (Multi-Exit Discriminator).
These are just a few examples, and the specific metrics and their calculations can vary between different routing protocols. Understanding how metrics are calculated and used is crucial for designing and optimizing network routing.
