Re: variance - another EIGRP question

Hi Piotr,

Let me break this down...

1- You use the variance command to indicate how "wide" the range of your
acceptable metric for forwarding purpose is. It simply means if you get 4
unequal metric paths where 3 of them do have the feasibility conditions,
then you can choose how many links out of those three you wish to utilize
using EIGRP.

2- From a real world point of view, you might have some links that you don't
want them to participate in the FWing process. If you choose 128 literally
it includes all feasible successors - which in turn may not be a desirable
result. From an exam point of view however, I'd go for the most precise
figure if it's happen to be 7 then my answer going to be 7. You can guess if
you wish but I would not take a risk like that (although it may work).

* If you need a real world example let me know.

HTH

Kambiz Agahian

CCIE Instructor/Consultant
M.Eng Telecom, CCIE# 25341, CCSI# 33326, MCSE, MCSA

On Thu, Oct 7, 2010 at 1:49 PM, Piotr Malarski
<piotr.malarski.99_at_gmail.com>wrote:

> Hello All,
>
> What is the meaning of variance ? I know that it enables unequal load
> balancing in EIGRP but what it really does ? What if I enter variance
> 128 (max value) instead of calculating it ? It looks to me that it
> works just fine.
>
> After some labbing I noticed that I can use variance to eliminate
> slower link from being load balanced when more than two links exist.
> See example below. I can however achieve the same result with
> "maximum-paths".
>
> Here is an example:
>
> R1
> / | \
> R2 R3 R4
> |------|------|
>
> R1-R2: 1,5 mb/s p2p 10.1.12.0/24
> R1-R3: 512 kb/s p2p 10.1.13.0/24
> R1-R4 <http://10.1.13.0/24%0AR1-R4>: 16 kb/s p2p 10.1.14.0/24
> R2-R3-R4: Ethernet 10.1.123.0/24
>
> Calculated variance between link R1-R2 and R1-R4 is 74. If I enter on
> R1 variance 73 only two faster link will work:
>
> I played with various variances on R1 with following results
>
> Case #1: Variance 73:
> Sh ip route:
> 10.0.0.0/24 is subnetted, 4 subnets
> C 10.1.14.0 is directly connected, Serial1/0.14
> C 10.1.13.0 is directly connected, Serial1/0.13
> C 10.1.12.0 is directly connected, Serial1/0.12
> D 10.1.123.0 [90/5537536] via 10.1.13.3, 00:00:01, Serial1/0.13
> [90/2195456] via 10.1.12.2, 00:00:01, Serial1/0.12
>
>
> Case #2: variance 74:
> 10.0.0.0/24 is subnetted, 4 subnets
> C 10.1.14.0 is directly connected, Serial1/0.14
> C 10.1.13.0 is directly connected, Serial1/0.13
> C 10.1.12.0 is directly connected, Serial1/0.12
> D 10.1.123.0 [90/160537600] via 10.1.14.4, 00:00:02, Serial1/0.14
> [90/5537536] via 10.1.13.3, 00:00:02, Serial1/0.13
> [90/2195456] via 10.1.12.2, 00:00:02, Serial1/0.12
>
> Case #: variance 128:
> 10.0.0.0/24 is subnetted, 4 subnets
> C 10.1.14.0 is directly connected, Serial1/0.14
> C 10.1.13.0 is directly connected, Serial1/0.13
> C 10.1.12.0 is directly connected, Serial1/0.12
> D 10.1.123.0 [90/160537600] via 10.1.14.4, 00:00:02, Serial1/0.14
> [90/5537536] via 10.1.13.3, 00:00:02, Serial1/0.13
> [90/2195456] via 10.1.12.2, 00:00:02, Serial1/0.12
>
>
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Received on Thu Oct 07 2010 - 14:22:32 ART