route behavior in equal cost path EIGRP


If there are 2 equal cost paths in the same EIGRP Process for the same destination, does it start load balancing straight away, if not which one will become the successor?

Where can I find the default bandwidth and metric values for the known type of interfaces as those are used by EIGRP metric.

Thanks in advance.

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It starts balancing straight away (you can see by doing a "sh ip route").

EIGRP uses this formula to calculate the metric:



bw=(10^7)/(bandwidth in kbs), taking the lowest bandwidth in the path

delay=delay in tens of microseconds, sum of delays for all links in the path

reliability=from 1 to 255, 255 means totally reliable

by default, the values of the constants are K1=1,K2=0,K3=1,K4=0,K5=0, so the [K5/(reliability+K4)] term is ignored and the formula becomes

metric = 256 * (bw + delay)

where bw and delay are calculated as described above. The bandwidth of an interface is configured with the "bandwidth" command in interface configuration mode, or defaults to 1544Kbs for serial interfaces, and to the ethernet speed for ethernet interfaces.

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To see the EIGRP topology table, use the "show ip eigrp topology" command. The EIGRP topology table will show all the routes known by EIGRP, including feasible successors, and metrics. Routes from the topology table will be inserted into the routing table if the topology entry is a better or equal cost route than the one in the routing table.

Load balancing is done in CEF on a per destination basis (as opposed to per packet), and can take from a few minutes to a few hours before you see the traffic load-balanced. Per destination load-balancing will never ever be

50/50. Before you immediately say, I'll switch to per-packet load-balancing, make sure you understand the ramifications. Some platforms perform per packet load balancing in software, and if you are running multicast you will run into issues with that as well.

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