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. Rene,

    i was working on the lab for myself. i have the exact same config. however my ports are different as i am using a different ios version router. my traceroutes would go from r1>r4>r5> where the 5.5.5.5 was at.

    after taking down a link i would get this output. what does this traceroute mean (below)

    Type escape sequence to abort.
    Tracing the route to 5.5.5.5

    1 192.168.12.2 108 msec
    192.168.13.3 88 msec
    192.168.12.2 44 msec
    2 192.168.35.5 112 msec
    192.168.25.5 72 msec
    192.168.35.5 120 msec

  2. my mistake. i found the issue. thank you for your quick response. layer 8 issue. lol

  3. Hello Rene

    I followed all the step but still see some issue in traceroutes .I guess if the destination is 5.5.5.5 and we are load balancing we have 2 path via R2 & R3 .why do I see both R2& R3 ip in the traceroute .

    ## traceroute :
    R1#traceroute 5.5.5.5
    
    Type escape sequence to abort.
    Tracing the route to 5.5.5.5
    
      1 192.168.13.3 64 msec
        192.168.12.2 64 msec
        192.168.13.3 64 msec
      2 192.168.25.5 60 msec
        192.168.35.5 64 msec
        192.168.25.5 60 msec
    R1#sh clock
    *14:34:04.131 UTC Sat Aug 19 2017
    
    
    
    R1#traceroute 5.5.5.5 source 192.168.13.1
    
    Type esc
    ... Continue reading in our forum

  4. Hello Rahul

    This is normal behaviour of traceroute when you have two equal cost routes. Traceroute sends ICMP packets and since both routes are equal, it will send them via both routes.

    So for your first attempt, you get the following:

    Note that f

    ... Continue reading in our forum

  5. Hi I was studying use of the ‘variance’ command when I noticed the following:

    Feasible Distance of R3 (feasible successor) = 41260
    I assume it should read 412160 - I’m aware it is a very minor point, but it might cause a little confusion to some people.

    regards
    Jeff

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