What is metric?
Routing protocol uses the metric to determine which route is best route for the destination. Some time router has more than one path for the destination network. To select the best path, the routing protocol must be able to evaluate and differentiate among available path. A metric is used to for this purpose. The metric determine which path is most preferable when there are multiple paths available for the same network. Different routing protocol uses different metrics such as RIP uses hop count, EIGRP uses bandwidth etc.
Metric parameter
Because each routing protocol uses the different metrics, two different routing protocols chooses different path to the same destination. The following are the metric parameter.
Hop count-It is a metric that define number of hop count means the number of the router that a packet must traverse to reach the destination.
Bandwidth-This metric select the path with the highest bandwidth.
Load-Consider the traffic utilization of a certain link.
Delay-Consider the time a packet takes to traverse a path.
Reliability-It is calculated from the interface error count or previous link failure.
Cost-It is a metric determined by the IOS or by administrator to indicate preference of the route.
Metric used by the protocols
RIP- This protocol uses the hop count to select the best path.
IGRP and EIGRP- These protocols uses bandwidth, delay, reliability and load. By default bandwidth and delay is used and the best path is chosen by the composite metric calculate from this two parameter.
OSPF-This protocol uses the bandwidth to determine the cost.
Metric can be viewed of each protocol by the command ‘show ip route’.
Load balancing
We know the metric are used to determined the best path for the remote network but if the two or three ways having the same metric ,in this case how the router decide which path is to use for the destination. This is done by the load balancing .The router load balances between this equal-cost path and the packet is forward using all equal cost-path. Load balancing divide the amount of work to be done in the same time. Load balancing can be implemented with the hardware, software or the combination of both. If the two servers are balance a work load, a server is needed to determine which server to assign the work to.
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