EIGRP Unequal Cost Load Balancing


(Rene Molenaar) #1

This topic is to discuss the following lesson:


(Networklessons Admin) #2

19 posts were merged into an existing topic: EIGRP Unequal Cost Load Balancing


(Rene Molenaar) #3

Thanks Paul, I just rewrote it a bit.


(Thomas K) #4

Rene,
Hi. If we set the variance to 11 it will begin load-balancing, but can you reconfirm the proportion it will be performing this (i.e. 11:1)?

Many thanks,
Thomas


(Rene Molenaar) #5

Hi Thomas,

I think this will be useful, it’s a configuration example:

The variance command is used to define which feasible successors will be used for load balancing but it doesn’t tell the router which proportion to use. The proportion is based on the feasible distance of the EIGRP routes that were placed in the routing table.

Rene


(Hussein Samir) #6

Hi Rene,

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

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 ) ?


(Rene Molenaar) #7

Hi Hussein,

It will be shared in proportion based on the feasible distance. If the successor had a FD of 100 and the feasible successors had a FD of 20 and 10 then you’d see a 10:2:1 ratio.

Rene


(Hussein Samir) #8

thanks Rene


(husam s) #9

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, minimum bandwidth is 100000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 2
  * 11.11.11.2, from 11.11.11.2, 00:01:11 ago, via Serial5/0
      Route metric is 640256, traffic share count is 59
      Total delay is 5010 microseconds, minimum bandwidth is 5000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1

Rene Molenaar September 17, 2015 at 13:29 #
Hi Hussein,

It will be shared in proportion based on the feasible distance. If the successor had a FD of 100 and the feasible successors had a FD of 20 and 10 then you’d see a 10:2:1 ratio.

Rene

REPLY


(Rene Molenaar) #10

Hi Husam,

There’s two entries for 2.2.2.0/24:

successor has a FD of 156516, feasible successor has a FD of 640256

640256 / 156516 = 4.09 so EIGRP will load balance over these routes in a 1:4.09 ratio, that’s the same as 59:240.

These numbers are a bit annoying to work with since EIGRP uses high metric values.

Rene


(husam s) #11

now i understand what you did


(husam s) #12

now if we want to improve this ratio we can change the K values so we make it only bandwidth and we change the bandwidth it will be better Right ?


(Rene Molenaar) #13

That’s right, you can play with the metrics (and/or K values) to change this.


(Eng_ A) #14

that was a very straight forward explanation. Thanks Rene :slight_smile:

 

Ammar,


(Lawrence O) #15

Hi Rene,

I’m always confused when I need to do traffic engineering on EIGRP routes.
Assuming if my router has 2 uplink connections and receive equal cost metric routes

How to we influence the route to use 1 particular connection for all the routes.
Do i reduce the delay on the inbound interface of the router or outbound interface of upstream router?

In addition, could we also have tutorial on Leak map and offset list?


(Rene Molenaar) #16

Hi Lawrence,

There’s three ways how you can accomplish this:

  • Play with the delay / bandwidth on one of the interfaces since it will influence the EIGRP metric.
  • Use an offset-list
  • Use filtering so that certain prefixes are not accepted on one of the two interfaces.
In this case, I would prefer the offset-list, it's simple to implement and when one of the links fails you can always use the other one. Here's an example how to configure it:

I’ll add the leak map to my list :slight_smile:

Rene


(Nikhil M) #17

Is the load balancing 1:1 on the unequal cost links after we use the EIGRP variance commands or will it be 10:1 in case the cost of 1 path is 100 and other is 10 ?


(Rene Molenaar) #18

With the default settings and the variance configured, EIGRP will distribute traffic proportionately to the ratios of the metrics of each router.


(RODRIGO H) #19

Awesome post !
On this case the balance will be 11:1 ?
What determines the proporcional of balance will the value configured on variance ?


(RODRIGO H) #20

Hello René !

Doens´t need to answer - I read the next topic “EIGRP Variance Command Example” and I understood !

Tks !