[Okta Webinar] Learn how to a build a cloud-first strategyRegister Now

x
?
Solved

EIGRP VARIANCE

Posted on 2011-10-26
12
Medium Priority
?
526 Views
Last Modified: 2012-05-12
I would like to understand the purpose of the EIGRP Variance command.
I did some reading, and it says the purpose of it is to Loadbalance EIGRP Traffic.

Let's say we have the following Routers:

A--10->B--20->C  FD=30
A--20->D--30->C  FD=50
A--30->E--30-->C FD=60

how does Variance command come into play in this case?

thanks


0
Comment
Question by:jskfan
  • 6
  • 4
  • 2
12 Comments
 
LVL 17

Accepted Solution

by:
Marius Gunnerud earned 1500 total points
ID: 37036458
Varience deals with unequal cost load balancing. when configuring the variance, EIGRP takes the varience that is configured and multiplies it by 20. In your example we would need to configure a varience of 30. 2 * 30 = 60.  This will set the minimum metric to reach router C to 60.  This means that all routes that are less than or equal to 60 will qualify to participate in unequal cost loadbalancing.

However, in your example A>B>C is the Successor and A>D>C is the Feasible Successor. there for only these two routes will be used when loadbalancing. Since A>E>C is not a Feasible Successor it will not participate in the loadbalancing.
0
 
LVL 17

Assisted Solution

by:rochey2009
rochey2009 earned 500 total points
ID: 37036699
Also, the router will load balance proportionally over unequal cost paths.
0
 

Author Comment

by:jskfan
ID: 37036920
when you use the variance:
30. 2 * 30 = 60

Now you are making the cost for A--10->B--20->C FD=60
and since
A--20->D--30->C  FD=50

would thisA--20->D--30->C FD=50   become the successor and the A--10->B--20->C FD=60 becomes the Feasible successors ? seeing that 50<60 ?

Also A--30->E--30-->C FD=60 , why this woulfd not be a Feasible Successors since it has the same FD as the old successor A--10->B--20->C FD=60

Thanks

0
Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 
LVL 17

Assisted Solution

by:Marius Gunnerud
Marius Gunnerud earned 1500 total points
ID: 37037050
first of all it is not 30.2 * 30.........it is 2 *30  The dot is a period.

Also notice I made a mistake in my previous post.  it was meant to be a configure a varience of 3, not configure a varience of 30.

----->would thisA--20->D--30->C FD=50   become the successor and the A--10->B--20->C FD=60 becomes the Feasible successors ? seeing that 50<60 ?

no, A>B>C is still the successor and A>D>C is still the feasible successor.  entering the variance 2 command only instructs the router to send traffic accross links that have a cost less than or equal to 60 but still meet the requirements of successor and feasible successor.

----->Also A--30->E--30-->C FD=60 , why this woulfd not be a Feasible Successors since it has the same FD as the old successor A--10->B--20->C FD=60

Again, the variance command doesn't change the existing cost, only tells the router which links to send traffic over.  Successor and feasible successor remain the same.
0
 
LVL 17

Assisted Solution

by:Marius Gunnerud
Marius Gunnerud earned 1500 total points
ID: 37037056
LOL ignor the following statement from my previous post.  Must not have gotten enough sleep last night :-D

----->Also notice I made a mistake in my previous post.  it was meant to be a configure a varience of 3, not configure a varience of 30.

0
 
LVL 17

Assisted Solution

by:Marius Gunnerud
Marius Gunnerud earned 1500 total points
ID: 37037065
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.
0
 

Author Comment

by:jskfan
ID: 37042922
Let me Recapitulate:

A--10->B--20->C  FD=30
A--20->D--30->C  FD=50
A--30->E--30-->C FD=60

with variance of 2 it will become
A--20->D--30->C  FD=50
(--10->B--20->C)*2  FD=60

A--30->E--30-->C FD=60

You are saying the Successor and FS  don't change. which means:
(--10->B--20->C)*2  FD=60  = Successor
A--20->D--30->C  FD=50 = feasible Successor

This means that all routes that are less than or equal to 60 will qualify to participate in unequal cost loadbalancing.
SO: A--20->D--30->C  FD=50 AND A--30->E--30-->C FD=60 will qualify.

Correct ??







0
 
LVL 17

Assisted Solution

by:Marius Gunnerud
Marius Gunnerud earned 1500 total points
ID: 37043245
Before variance:
A--10->B--20->C metric=30
A--20->D--30->C metric=50
A--30->E--30-->Cmetric=60

A variance of 3 means that any route with a metric less than the best metric (minimum metric) to a destination multiplied by the variance, and meets the feasibility condition, will be added to the routing table.

After variance 3 is added:
A--10->B--20->C metric=30
A--20->D--30->C metric=50
A--30->E--30-->Cmetric=60

The command doesn't change the metrics or FD of the routes but instead tells the router to include paths to a destination that meet the conditions. route A>E>C is not included in the routing table because it doesn't meet the feasibility conditions.
0
 
LVL 17

Assisted Solution

by:rochey2009
rochey2009 earned 500 total points
ID: 37047123
Hi,

Variance is used by EIGRP to decide which routes are placed from the EIGRP topology table into the routing table. With a variance of 1 which is the default, only routes which have the lowest metric are placed into the routing table. If there are multiple paths with this same lowest metric then these are also placed into the routing table and load balanced equally.

If you increase the variance to 2, then EIGRP will multiply the lowest cost path by 2 and will place routes which are less than or equal to this into the routing table. EIGRP will only consider paths which it determines to be loop free i.e. those which meet the Feasibility Condition. EIGRP will load balance unequal cost paths proportionally.
0
 

Author Comment

by:jskfan
ID: 37081102
Before variance:
A--10->B--20->C metric=30
A--20->D--30->C metric=50
A--30->E--30-->Cmetric=60
 
After variance 3 is added I guess it will be:
A--10->B--20->C metric=90
A--20->D--30->C metric=50
A--30->E--30-->Cmetric=60


in this case either the Variance 3 is too high or thelinks below will also be added to the topolgy table and there will be an unequal cost balancing between all 3 links:
                           
A--20->D--30->C metric=50
A--30->E--30-->Cmetric=60



0
 
LVL 17

Assisted Solution

by:Marius Gunnerud
Marius Gunnerud earned 1500 total points
ID: 37081340
Before variance:
A--10->B--20->C metric=30
A--20->D--30->C metric=50
A--30->E--30-->Cmetric=60

After variance 2 is added:
A--10->B--20->C metric=30
A--20->D--30->C metric=50
A--30->E--30-->Cmetric=60

The metrics DO NOT change. The variance command only tells the router which links to include in the unequal cost loadbalancing that also meet the feasibility condition.

Yes, in this scenario variance 3 is too high but the result would still be the same.  Since A > E > C does not meet the feasibility condition it would not be included anyway.
0
 

Author Closing Comment

by:jskfan
ID: 37098406
Thank you Guys1
0

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

I eventually solved a perplexing problem setting up telnet for a new switch.  I installed a new Cisco WS-03560X-24P switch connected to an existing Cisco 4506 running a WS-X4013-10GE Sup II-Plus. After configuring vlans and trunking,  I could no…
I recently attended Cisco Live! in Las Vegas, a conference that boasted over 28,000 techies in attendance, and a week of hands-on learning hosted by a solid partner with which Concerto goes to market.  Every year, Cisco displays cutting-edge technol…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…

873 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question