EIGRP Variance Confused

[helpmeplz]

Dear Experts,

I have confusion about Variance Command. Suppose

When we configure variance under router Eigrp 10 (etc Whatever it can be)

Variance 10

I am confused when we will confiuge this it will apply this on all links but i want to load balance to only over 2 links not all of them advertised under eigrp.

Mean to say want to un equal load balanace on some specific link not all of them.

[InayathUlla Sharieff]

           

Hi,

Let me try to explain you.

Variance allows the router to include routes with a metric smaller than the multiplier times the minimum metric route to that destination.

There are two types of load balancing:

Equal cost path – Applicable when different paths to a destination network report the same routing metric value. The maximum-paths command determines the maximum number of routes that the routing protocol can use.

Unequal cost path – Applicable when different paths to a destination network report are of different routing metric values. The variance command determines which of these routes is used by the router.

Every routing protocol supports equal cost path load balancing. In addition, Interior Gateway Routing Protocol (IGRP) and EIGRP also support unequal cost path load balancing. Use the variance n command in order to instruct the router to include routes with a metric of less than n times the minimum metric route for that destination. The variable n can take a value between 1 and 128. The default is 1, which means equal cost load balancing. Traffic is also distributed among the links with unequal costs, proportionately, with respect to the metric.

Please go through the below links once and let me know if you find any difficulty in understandng the same:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml

https://supportforums.cisco.com/docs/DOC-23674

http://gns3vault.com/EIGRP/eigrp-maximum-path-and-variance.html

2- Regarding your question when you configure Variance 10 what happens:

Eg: Suppose you have 4 links from R1 to reach R5

1- The best path(FS) to reach from R1 to R5 is 2.

2- Variance of 10( 10*2=20) so which ever link falls under cost below 20 or equals to 20 will be load balance.

HTH

Regards

Inayath

*Plz rate the usefull posts.

[Vinayaka Raman]

I am not aware of any method that set variance for specific subnet...the variance will be a multiplication factor that will make feasible successors will also get into forwarding table when you choose correct value.. But I don't think this can be made applicable only for specific entries in a topology table..please some more information to see what can be done..

What is your topology look like ?
You need to consider return path as well
Show ip eigrp topology x.x.x.x/x on either sides
Please do remember eigrp will consider minimum bandwidth when choosing paths..


Sent from Cisco Technical Support iPad App

[helpmeplz]

Lets Assume

I have Site A  and Site B Connected with Two Links.

Active is of 100mb and Standby is of 20mb.

I have another Site C

It is connected to Site B with 15mb and connected to Site B with 10mb.

Site A (Vlan 192.168.3.x)

Site B (Vlan 192.168.4.x)

Site C (Vlan 192.168.5.x)

Now when we will calcaulate variance and apply under eigrp it will apply for Site A B and C if i am rite.

But i want uneqal Load balancing for jst Site C not for Site B.

From Site A Traffic Goes to 100mb to Site B and From There to Site C Via 15mb

From Site A traffice Goes to Site C Via 10mb.

Unequal cost loadbalacnign for slelected links.

What i understand from varian command is it applies loadbalancing on all links.

Dear Experts....

Please suggest.....

[cadet alain]

Hi,

You can use  the  traffic-share min across-interfaces if you want to use only the minimum cost paths.

if the paths you want to use are already the minimum cost then you have nothing more to do otherwise you'll have to tweak EIGRP with either an offset-list or manipulating Delay to make the undesired path the maximum cost path.

Regards.

Alain

Don't forget to rate helpful posts.

[frangkoyski]

all i can say to you regarding variance is that you have to be aware of the metrics of your eigrp links. First of all, the variance command works by multiplying your successors FD to a number you prefer until it will be equal or higher to the FD value of the link you desire to have an equal load balance with.  For example.  If your successor FD is 500 and your Feasible Successors FD is 1500, you just do the command "variance 3" and it will multiply your FD w/c is 500 x 3 w/c is equal to 1500 also. that will enable it to have a load balance. And just to add, if your curious about "traffic count" , it is the ratio of distribution of load balance. so, that means if your successors FD is 500 and you Feasible Successors FD is 1500.  1500/500 = 3 . so your traffic share count of your successor will be 3 and your feasible successors traffic share count will be 1. that means,as an example, in every 1kbps  that flows in your feasible succesor route, 3kbps will flow on the Successor route. :)