Re: variance - another EIGRP question

Great blogs from ipexpert on EIGRP technology.

http://blog.ipexpert.com/2010/05/03/eigrp-unequal-cost-load-balancing/
http://blog.ipexpert.com/2010/03/03/eigrp-metric-k-values/

--
Garry L. Baker
"There is no 'patch' for stupidity." - www.sqlsecurity.com
On Thu, Oct 7, 2010 at 3:49 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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