This article explains EIGRP authentication and load balancing. The problem of unequal-cost load-balancing. Have you ever wondered why among all IGPs only EIGRP supports unequal-cost load balancing. For CCNA and CCNP candidates alike! In this lab, we'll go over EIGRP unequal-cost load balancing theory, and then put that theory into action in a lab with live.


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EIGRP For The CCNA: Unequal-Cost Load Balancing Lab

So if you saw a 2 or a eigrp load balancing or a 4, and usually you stick to 2 in eigrp load balancing. Because you will only load balance unequally when you have feasible successors.

And the math works out that your feasible successors are still probably not going to be like 50 times worse than your successor. Because of the way that the DUAL algorithm would probably exclude that from being a feasible successor.

EIGRP authentication & load balancing

So if we saw a variance of 2, that would mean we eigrp load balancing go two times source. In eigrp load balancing of the metric, it could be double.

If I see a variance of 3, it could be triple. The metric of the feasible successor could be triple and we would trickle down some traffic. And it is a trickle, it is not going to try to send the same amount, it is going to proportionally load balance. So this is a really intelligent mechanism.

That is the reality, it really is. In a production network, you don't want to just go out and do this especially if you have sensitive traffic.

Load Balancing on EIGRP - Cisco Community

If your traffic is sensitive to quality of service, then imagine sending some IP phone calls across your primary WAN and then, you got your eigrp load balancing phone calls for IP telephony. Your CEO's phone call getting load balanced on the feasible successor and that feasible successor is already at capacity - could be pretty bad and it could be hard to enforce quality of service for that.


This value defines how many paths can be used for load balancing to a single eigrp load balancing. Time for that second vital variance tip! Path 1 has a metric ofPath 2 a metric ofand Path 3 a metric of Do you really want to load balance over that third path?

With unequal-cost load balancing in effect, the load each link carries is proportional to the eigrp load balancing. Router R1 receives the two routing updates for the subnet Router R1 places both routes in the routing table and load balances across three links.

You can verify that R1 is indeed using both paths by typing the show ip route command: You can set up your router to load balance over eigrp load balancing with different metric to reach a destination.

To accomplish unequal-cost load balancing, the variance command is used.

EIGRP For The CCNA: Unequal-Cost Load Balancing Lab

The command takes one parameter, the multiplier, which tells the router to load balance across each link with the metric for the destination less than the feasible distance eigrp load balancing by the multiplier value.

NOTE The multiplier value, by default, is 1. This ensures equal utilization of the links, but is a processor intensive task and impacts the eigrp load balancing forwarding performance.

This form of per-packet load balancing is not well suited eigrp load balancing higher speed interfaces. Per-destination or per-packet load-balancing depends on the type of switching scheme used for IP packets.


By default, on most Cisco routers, fast switching is enabled under interfaces. This is a demand caching scheme that does per-destination load-balancing. To set per-packet load-balancing, enable process switching or disable fast switchinguse these commands: This can crash a low-end router because the Eigrp load balancing must do all the processing.


To re-enable fast switching, use these commands: However, it does imply that you have the extra resources to deal with maintaining CEF entries and adjacencies.