what the VARIENCE does under EIGRP Process?

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HI Expert's!

If you wanted to send traffic over both links you would need to use the variance command under the EIGRP PROCESS

what the VARIENCE does under EIGRP Process?

10xs

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Correct Answer by Jon Marshall about 9 years 7 months ago

Hi Ali

Okay firstly you need to obtain the metric for the L3 etherchannel route. You can get this from the routing table -

"sh ip route x.x.x.x x.x.x.x".

Find the route entry and the second figure in the square brackets so it should be [90/xxxxxx]. You are interested in the xxxxxx figure.

Secondly you need to see if the second connection is in the EIGRP topology table because if it isn't it will need to be and you may to manipulate the metrics to get it there.

"sh ip eigrp topology" will show you the EIGRP topology table. If the route via the 300M link is in there note down the metric.

Next you need to work out how many times you need to multiply the metric of the best route to get to the metric of the 300m link. This is your variance figure.

If the route for the 300M link is not in the EIGRP topology table you will need to adjust the metrics to get it there. See Narayan's post from previous EIGRP discussion on what you need to do.

HTH

Jon

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Jon Marshall Fri, 02/16/2007 - 07:56

Hi Ali

If EIGRP has equal cost paths to a destination network it will install both of them in the routing table and use them both. This is the same behaviour as other IGP's.

But EIGRP can also load balance across unequal cost paths as well. It it is all to do with the metric's of the routes. So for example

Router A has two routes to network Z. The first route has a metric of 1000, the second has a metric of 2000. Under normal operations only the route with the metric of 1000 will be installed in the routing table.

However, if you want to use both links then you can use the variance command. The variance is a multiplier so if the best metric is 1000 a and the second best is 2000 then the multiplier will be 2 ie 2 x 1000 = 2000.

Then EIGRP will load balance across both links at a 2:1 ratio.

Note that for a route with a lesser metric to be used for load-balancing with the variance command the route must be a feasible successor already in the EIGRP topology table.

HTH

Jon

devang_etcom Fri, 02/16/2007 - 08:24

hi ali,

just go for routing table and find out the lowest level metrics or cost and then multiply by the integer which should be equal or greater than the maximum cost.... for example... you have three link of verious cost like

5,9 and 14... normally routing protocol prefer the lowest cost pasth so here 5 is the best path for the routing protocol... so only path with cost5 will come in to the routing table and used for routing... but when you want to use two link which is of cost 5 and 9 then you need to go for veriance command at that time you have to go for the veriance of 2 as lowest cost(5)X veriance(2)=10... so here in routing table you will have all the path with the cost below the 10 so in our case its path with cost 5 and 9 will apear in the routing table... if you want all the three path for the loadbalancing then you have to go for the variance of 3... so now lowest cost(5)X variance(3)=15... it means all the path with the cost lower then 25 will come in to the routing table... so in our case you will have 5,9 and 14 cost path in your routing table... so you can do it by your self by finding the lowest cost and then multiply by appropriate variance integer...

hope this will help you

regards

Devang

Correct Answer
Jon Marshall Fri, 02/16/2007 - 08:24

Hi Ali

Okay firstly you need to obtain the metric for the L3 etherchannel route. You can get this from the routing table -

"sh ip route x.x.x.x x.x.x.x".

Find the route entry and the second figure in the square brackets so it should be [90/xxxxxx]. You are interested in the xxxxxx figure.

Secondly you need to see if the second connection is in the EIGRP topology table because if it isn't it will need to be and you may to manipulate the metrics to get it there.

"sh ip eigrp topology" will show you the EIGRP topology table. If the route via the 300M link is in there note down the metric.

Next you need to work out how many times you need to multiply the metric of the best route to get to the metric of the 300m link. This is your variance figure.

If the route for the 300M link is not in the EIGRP topology table you will need to adjust the metrics to get it there. See Narayan's post from previous EIGRP discussion on what you need to do.

HTH

Jon

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