EIGRP Unequal Cost Load Balancing

Just like OSPF or RIP, EIGRP can do load balancing but it has one more trick in its hat. RIP and OSPF both can do load-balancing but the paths have to be equal.

EIGRP can do something cool…unequal load-balancing! Even better it will share traffic in a proportional way, if you have a feasible successor that has a feasible distance which is 5 times worse than the successor then traffic will be shared in a 5:1 way.

Let’s take a look at an example of how EIGRP can do load balancing:

Eigrp Unequal Cost Load Balancing Topology

We’ll view this topology from R1’s perspective. Let’s fill in the successor, feasible successor, advertised and feasible distance in a table. If you have no idea how this works please read my introduction to EIGRP first.

 

Advertised Distance

Feasible distance

 

R2

15

20

R3

10

15

SUCCESSOR

R4

14

114

FEASIBLE SUCCESSOR

This is our first example where we found out the successor and feasible successor. If you look at the routing table you will only find the successor there. Now we are going to change things so we’ll see the feasible successor in the routing table as well so it will load-balance.

You can do this by using the variance command. The variance command works as a multiplier:

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Forum Replies

  1. Hi Rene,

    If we have three path to destination and we configure variance to use the three path just like in your example here :-

    https://networklessons.com/eigrp/eigrp-variance-command-example/

    My question is :-
    The traffic will be shared in which way ? to be more clarify, In the begging of this article you said " if the feasible successor has a feasible distance which is 5 times worse than the successor then traffic will be shared in a 5:1 way " so what the rate will be if we have three path to destination ( the successor and tow feasible successors ) ?

  2. i didn’t understand this
    could you explain more details about this . that will be hard when the numbers are high .
    and i show command its show me share count

    Router#show ip route 2.2.2.2
    Routing entry for 2.2.2.0/24
      Known via "eigrp 1", distance 90, metric 156416, type internal
      Redistributing via eigrp 1
      Last update from 192.168.0.1 on FastEthernet0/0, 00:01:11 ago
      Routing Descriptor Blocks:
        192.168.0.1, from 192.168.0.1, 00:01:11 ago, via FastEthernet0/0
          Route metric is 156416, traffic share count is 240
          Total delay is 5110 microseconds
    ... Continue reading in our forum

  3. Hello Florain

    The FS is a FS only if it is not in the routing table. If it is in the routing table it has the best metric and is thus considered a successor, even if there are more than one such as is the case with EIGRP load balancing.

    ... Continue reading in our forum

  4. Hello Marcel

    All routes learned via EIGRP are contained within the topology table, whether they are actively being used (in the routing table) or not. These routes are examined by EIGRP and only the route with the best metric is placed within the routing table. The rest of the routes still exist in the topology table however.

    So, the routing table will only have a single route to a particular destination by default (unless two routes have an equal metric of course). In order to determine if a route can be used for unequal load balancing, the variance value i

    ... Continue reading in our forum

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