LAB Scenario - Eigrp

Unanswered Question
Mar 10th, 2010


LAB Scenario - Eigrp Load Balancing on unequal Bandwidth

LAB Diagram attach

Can I get correct steps to enable load balancing on unequal bandwidth



I have this problem too.
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Giuseppe Larosa Wed, 03/10/2010 - 12:28

Hello Tom,

first of all the worse path must satisfy the fesibility condition advertised distance < Feasible distance

in your case this is fine because both links are to the same router.

EIGRP metric is directly proportional to cumulative delay and inversely proportional to lowest bandwidth on path

256 * (sum of delays in tens of microseconds) + 256 * ( 10^7 / minBw [kbps])

you can use sh ip eigrp topology to see advertised distance and distance calculated on local node

the command to be used under router eigrp process is

variance M

the calculated distance on local node for the backup path has to be less then M the feasible distance (best metric to IP prefix on local node)

in your case M can be calculated as the ratio of bandwidths on the two links

1544 / 256  = 6,034

I would use M = 7 in your case to be sure that secondaryt path will be used

if delay is the same on the two serial interfaces you can check this with

sh interface s0.1

sh interface s0.3

you need to use the above command on both routers Earhart and Cochran under router eigrp process

if delay is different the ratio can be greater between the two metric values.

Hope to help


tomfree_leo Thu, 03/11/2010 - 01:20

Hi Guislar for perfect explanation

which is practically more stable per session or per link loadbalancing. what configuration is needed for per session loadbalancing & per link loadbalancing

Thanks for your help


Giuseppe Larosa Thu, 03/11/2010 - 03:06

Hello Tom,

per packet load balancing is not recommended it can cause out of order

default CEF flow based is enabled by default

to enable per packet CEF load balancing in interface mode

interface type x/y

ip load-sharing per-packet

note: not all platforms support it.

you should be fine with CEF flow based that makes the exor of IP SA, IP DA and an hash

Hope to help


tomfree_leo Thu, 03/11/2010 - 04:28

Thank you  Giuseppe

Have a look at the attached design.

its simpler having one edge router but how do switch forward packets equally on both edge router connecting to remote Router.

Next Lab its redistribution,

OSPF between L3Switch & Edge Router

EIGRP between Edge Router and Remote Router

This is complex, how can help to understand.



Giuseppe Larosa Thu, 03/11/2010 - 06:01

Hello Tom,

if you are using EIGRP the same rules described in first post applies to this scenario to the EIGRP domain.

edge routers should talk both EIGRP and OSPF and to redistribute between them

EIGRP requires the setting of a seed metric using metric components

OSPF requires the use of subnet keyword

on both edge routers

router ospf 10

red eigrp 100 subnets type 1

router eigrp

red ospf 10

default-metric 10000 1000 255 1 1500

! seed BW, delay, reliability, MTU and load

In real world you would consider to use OSPF everywhere and to leave slower link as a backup path.

safer and simpler to troubleshoot

Hope to help



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