EIGRP metric calcualation

Answered Question
Aug 8th, 2010
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Hi!


I just wondered about this:


P 10.26.0.0/24, 1 successors, FD is 284160
        via 10.12.34.2 (284160/281600), FastEthernet2/0
        via 10.12.0.2 (307200/281600), FastEthernet0/1


Why the FD = RD + 256*Delay, but not FD = RD + 256*Delay + 256*(10000000/BW)?


So this means that on the local router I can play only with delay to influence metric?


EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0


Thank's

Roberts

Correct Answer by Giuseppe Larosa about 6 years 9 months ago

Hello Roberts,


only the lowest BW on path is used for the EIGRP metric calculation and indeed the received update contains in separate fields all the metric components with their value from the point of view of ther neighbor (RD)


if the interface to neighbor bandwitdth is greater or equal to the lowest bandwidth in path that part of the EIGRP metric does not change.


As a result of this the safer way to  change EIGRP metric is to play with delay as you have correctly noted, changing the bandwidth does not provide  a guarantee to change the total metric calculation.


delay is the sum of all delays on path


cumulative in delay and inverse proportional to lowest bandwidth in path this is EIGRP metric


Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Sun, 08/08/2010 - 07:20
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Hello Roberts,


only the lowest BW on path is used for the EIGRP metric calculation and indeed the received update contains in separate fields all the metric components with their value from the point of view of ther neighbor (RD)


if the interface to neighbor bandwitdth is greater or equal to the lowest bandwidth in path that part of the EIGRP metric does not change.


As a result of this the safer way to  change EIGRP metric is to play with delay as you have correctly noted, changing the bandwidth does not provide  a guarantee to change the total metric calculation.


delay is the sum of all delays on path


cumulative in delay and inverse proportional to lowest bandwidth in path this is EIGRP metric


Hope to help

Giuseppe

ropakalns Sun, 08/08/2010 - 23:48
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Actually, that makes a perfect sense.


Thank's,

Roberts

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