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By default, EIGRP will choose the path with the lowest metric. For this topology, the Point to point link between R1-R3 is 1.536 Mbps, frame-relay link between R2-R3 is 1.28 Mbps and the frame-relay link between R1-R2 is 256Kbps. In this scenario, R1 will choose Path 1 to reach VLAN 26. At this point if we configure the variance of 5, then the traffic will be load balanced between the two paths at a ratio of 80:23 as shown in the output below.
RSRack1R1#sh ip route 164.1.26.6
Routing entry for 164.1.26.0/24
Known via “eigrp 100″, distance 90, metric 3026432, type internal
Redistributing via eigrp 100
Last update from 164.1.12.2 on Serial0/0, 00:00:56 ago
Routing Descriptor Blocks:
* 164.1.13.3, from 164.1.13.3, 00:00:56 ago, via Serial0/1
Route metric is 3026432, traffic share count is 80
Total delay is 40100 microseconds, minimum bandwidth is 1280 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
164.1.12.2, from 164.1.12.2, 00:00:56 ago, via Serial0/0
Route metric is 10514432, traffic share count is 23
Total delay is 20100 microseconds, minimum bandwidth is 256 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
To achieve a 5:1 ratio, we can modify the metric through R2 to be 5 times the metric through R3. But before we can do that, let’s figure out how the metric is being calculated in the first place.
Metric = [K1*BW+(K2*BW)/256-Load)+K3*Delay]*[K5/(Reliability+K4)]
As we know, by default K1 and K3 equals 1 while all the other values are ZERO. So we can modify the above equation as follows:
Metric_R3 = (10^7/BW+Delay/10)*256
Metric_R3 = (10^7/1280+40100/10)*256
Metric_R3 = 3026432
In order to get the 5:1 ratio, we must increase the metric through R2 to be 5 times that of the metric through R3. This is how we can get the value of the DELAY through
R2.
Metric_R2 = Metric_R3 * 5
(10^7/BW+Delay/10)*256 = (10^7/BW+Delay/10)*256*5
(10^7/256+Delay/10) = (10^7/1280+40100/10)*5
(39062.5+Delay/10 = (7812.5 + 4010) * 5
Delay/10 = 59112.5 – 39062.5
Delay = 20050 * 10
Delay = 200500
Looking through the routing table, we can see that we already have a delay of 100 microseconds to reach VLAN26.
http://www.ccietalk.com/2008/09/21/eigrp-unequal-cost-load-balancing
and
http://blog.ipexpert.com/2010/05/03/eigrp-unequal-cost-load-balancing/
however, to get what should be the delay it's pretty easy
r2_delay = (10 ^ 7/min-bw-via-R3 + (delay-(r1-r3) + delay(r3+r2) ) /10 )*5
By default, EIGRP will choose the path with the lowest metric. For this topology, the Point to point link between R1-R3 is 1.536 Mbps, frame-relay link between R2-R3 is 1.28 Mbps and the frame-relay link between R1-R2 is 256Kbps. In this scenario, R1 will choose Path 1 to reach VLAN 26. At this point if we configure the variance of 5, then the traffic will be load balanced between the two paths at a ratio of 80:23 as shown in the output below.
RSRack1R1#sh ip route 164.1.26.6
Routing entry for 164.1.26.0/24
Known via “eigrp 100″, distance 90, metric 3026432, type internal
Redistributing via eigrp 100
Last update from 164.1.12.2 on Serial0/0, 00:00:56 ago
Routing Descriptor Blocks:
* 164.1.13.3, from 164.1.13.3, 00:00:56 ago, via Serial0/1
Route metric is 3026432, traffic share count is 80
Total delay is 40100 microseconds, minimum bandwidth is 1280 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
164.1.12.2, from 164.1.12.2, 00:00:56 ago, via Serial0/0
Route metric is 10514432, traffic share count is 23
Total delay is 20100 microseconds, minimum bandwidth is 256 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
To achieve a 5:1 ratio, we can modify the metric through R2 to be 5 times the metric through R3. But before we can do that, let’s figure out how the metric is being calculated in the first place.
Metric = [K1*BW+(K2*BW)/256-Load)+K3*Delay]*[K5/(Reliability+K4)]
As we know, by default K1 and K3 equals 1 while all the other values are ZERO. So we can modify the above equation as follows:
Metric_R3 = (10^7/BW+Delay/10)*256
Metric_R3 = (10^7/1280+40100/10)*256
Metric_R3 = 3026432
In order to get the 5:1 ratio, we must increase the metric through R2 to be 5 times that of the metric through R3. This is how we can get the value of the DELAY through
R2.
Metric_R2 = Metric_R3 * 5
(10^7/BW+Delay/10)*256 = (10^7/BW+Delay/10)*256*5
(10^7/256+Delay/10) = (10^7/1280+40100/10)*5
(39062.5+Delay/10 = (7812.5 + 4010) * 5
Delay/10 = 59112.5 – 39062.5
Delay = 20050 * 10
Delay = 200500
Looking through the routing table, we can see that we already have a delay of 100 microseconds to reach VLAN26.
http://www.ccietalk.com/2008/09/21/eigrp-unequal-cost-load-balancing
and
http://blog.ipexpert.com/2010/05/03/eigrp-unequal-cost-load-balancing/
however, to get what should be the delay it's pretty easy
r2_delay = (10 ^ 7/min-bw-via-R3 + (delay-(r1-r3) + delay(r3+r2) ) /10 )*5