eigrp between 2 sites using 2 routers

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Sep 10th, 2009
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Hi all


If I have 2 routers between site A and B, 1 is a 2 meg and the other a 1 meg line, as they are on different routers, will they both maintain successor routes of themselves? or can one of the routers still act as a feasible successor? I would have thought that both routers will be active. or ?

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Giuseppe Larosa Fri, 09/11/2009 - 03:26
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Hello Carl,


EIGRP feasibility condition requires that the reported distance (the metric from the point of view of the candidate node) has to be strictly lower then the feasible distance.

the feasible distance is the current best metric to the destination on the local node.

In this case best metric is that via 2Mbps link.

the reported distance on both links is the same value.


So the second path should provide a feasible successor but it is not used until variance command is not applied under the router eigrp process.

router eigrp xx

variance 3

! or higher


can make the 1Mbps link used for 1/3 of IP flows between the two sites.


This enables weigthed load balancing over links of different costs that is specific of EIGRP protocol.


Hope to help

Giuseppe


carl_townshend Fri, 09/11/2009 - 04:20
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Hi there

As there are seperate routers for the connection, would they both not have a route ? , but from say routers A point of view on site A, It would use its own as its got the 2 meg, and use router B as the feasible successor? but what would router B with the 1 meg link routing table look like ?


cheers

Giuseppe Larosa Fri, 09/11/2009 - 11:43
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Hello Carl,

if 4 routers are involved and the two links 1 Mbps and 2 Mbps the scenario changes again:


RA1 ---- RB1 2 Mbps

RA2 ---- RB2 1 Mbps


RA1 and RA2 share a vlan and talk EIGRP over it.

RA2 reported distance cannot satisfy feasibility condition it is bigger then best metric on RA1.


RA1 might be a feasible successor from the point of view of RA2 or even can be the successor for RA2 itself.


Hope to help

Giuseppe


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