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Redundant Link Calculation
Nov 27,2008 00:00
by
alperen
Redundant Link Calculation The topology database stores all known routes to a destination and the metrics used to calculate the least-cost path. Once the best routes have been calculated, they are moved to the routing table. The topology table can store up to six routes to a destination network, meaning that EIGRP can calculate the best path for up to six redundant paths. Using the known metrics to the destination, the router must make a decision as to which path to make its primary path and which path to use as a standby or secondary path to a destination network. Once the decision is made, the primary route—the one with the lowest metric—will become the successor and be added to the routing table. Any route that has an advertised distance lower than the successor’s feasible distance will become a feasible successor route. The path-cost calculation decisions are made from information contained in the routing table using the bandwidth and delay from both the local and adjacent routers. Using this information, a composite metric is calculated. The local router adds its cost to the cost advertised by the adjacent router. The total cost is the metric. Figure 4.4 shows how cost is used to select the best route (successor) and the backup route (feasible successor). |