Unequal cost load sharing via Eigrp

[ahmedmahmoud22]

I am trying to verify the Unequal cost load sharing configured between two routers, as per the below show 

R1#sho ip rou 192.168.17.1

Routing entry for 192.168.17.0/24

  Known via "eigrp 15", distance 90, metric 2297856, type internal

  Redistributing via eigrp 15

  Last update from 172.20.15.10 on Serial0/2, 00:26:51 ago

  Routing Descriptor Blocks:

    172.20.15.10, from 172.20.15.10, 00:26:51 ago, via Serial0/2

      Route metric is 10639872, traffic share count is 13

      Total delay is 25000 microseconds, minimum bandwidth is 256 Kbit

      Reliability 255/255, minimum MTU 1500 bytes

      Loading 1/255, Hops 1

  * 172.20.15.6, from 172.20.15.6, 00:26:51 ago, via Serial0/1

      Route metric is 2297856, traffic share count is 60

      Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit

      Reliability 255/255, minimum MTU 1500 bytes

      Loading 1/255, Hops 1

Traffic load share is 60:13 , means after each 60 packet throu one route , 13 packets will be sent throu the other route ,, Can any one confirm, why the rate comming like this , as i am receiving in the other couple router rate of 4:1 as below

R2#sho ip rou 192.168.16.1

Routing entry for 192.168.16.0/24

  Known via "eigrp 15", distance 90, metric 2809856, type internal

  Redistributing via eigrp 15

  Last update from 172.20.15.9 on Serial0/1, 02:43:33 ago

  Routing Descriptor Blocks:

    172.20.15.9, from 172.20.15.9, 02:43:33 ago, via Serial0/1

      Route metric is 11151872, traffic share count is 1

      Total delay is 45000 microseconds, minimum bandwidth is 256 Kbit

      Reliability 255/255, minimum MTU 1500 bytes

      Loading 1/255, Hops 2

  * 172.20.15.5, from 172.20.15.5, 02:43:33 ago, via Serial0/0

      Route metric is 2809856, traffic share count is 4

      Total delay is 45000 microseconds, minimum bandwidth is 1544 Kbit

      Reliability 255/255, minimum MTU 1500 bytes

      Loading 1/255, Hops 2

[vijay.swaminathan · Accepted solution]

Well my understanding is, it all depends on the metric.

since the route learnt via 172.20.15.6 has a better metric 2297856 than learnt via 172.20.15.10 (10639872).

The traffic share in this case is: 10639872/2297856 which roughly comes to 4.6 . so my guess is instead of mentioning it in decimals they would have taken the LCM of it and shown as a whole number 60 and 13

when you divide 60/13 you end up with the same result as 10639872/2297856

in the other case the equation (as cited above) comes close to a whole Number (4) so the IOS would have just represented that as '4'

This is just my guess... But will let the experts to comment / validate.

-Vijay

[John Blakley · Accepted solution]

Vijay is correct. The metric is used in deciding how many packets to send. The lower the metric means the more packets will be sent in favor of using the higher metric path.

Here's a link to verify:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml#traffic

John