If you have been given two links, one with 2 Mbps & another is 512Kbps. How would you load balance in the below ratio with EIGRP?
- 5:2
- 4:3
What does the above mean is, for 5 packets sent on 2 Mbps link, 2 packets should be sent over 512Kbps. Same with the next ratio, 4 packets sent over 2 Mbps, 3 packets should be on 512Kbps
Look at the below diagram
Look at the below diagram
By looking at the diagram, we notice there are two paths to reach R4's Loopback 0 interface 1.1.1.1/32. One is via the Fastethernet interface & another via serial interface. So, what are the technical stuffs coming into your end w.r.t EIGRP. Assume only "Delay" parameter is used to perform the composite metric calculation.
1) Path via R2 is the preferred path currently as the Delay parameters are least.
2) Path via R3 is the feasible successor because the Relative distance advertised by R3 to R1 is the same as advertised by R2 to R1. (i.e 100 + 5000 = 5100)
What is that we can do in order for path via R3 to be used for load balancing? To achieve this, we need to use EIGRP variance feature. Lets calculate the metric to reach R4's loopback from R1 manually. Below is the formula
Metric = 256 * (Sum of Delay/10)
Note : Delay is in tens of microseconds
Metric via R2 is = 256 * (100+100+5000)/10 = 133120
Metric via R3 is = 256 * (20000 + 100 + 5000) = 642560
So, we know that Metric via R2 will be the preferred path of the least Feasible distance. So, lets use our R3 path as well.
Remember, Variance = FD of the Feasible successor / FD of the successor
So, Variance = 642560/133120 = 4.82
Lets round that up to a whole number. So, Variance = 5
Now, by setting variance 5 under the EIGRP routing process, you would have the load balancing between two paths up.
Note : For the variance command to take effect, the path must be a feasible successor
But how to achieve 5:2 or 4:3 ratio load balancing? For this to happen, you need to consider the below things
1) How much delay should be set on the path via R3(the serial interface path) in order to get 5:2 ratio?
2) What would be the calculation to obtain the delay value?
To calculate the delay, below is the formula
Lowest Metric * = 256 * [delay/10]
* Lowest Metric is the path with the lowest feasible distance (in our case path via R2)
133120 * (5/2) = 256 * [delay]/10
332800 = 256 * [delay/10]
332800/256 = delay/10
1300=delay/10
13000=delay
Maths :)
The above delay value we calculated is the delay of the entire path (end-to-end). Now, we need to determine the delay value of the local interface. To find that, you need to subtract the advertised delay received from R3.
So, it would be 13000-5100 = 7900
The actual delay to be set on the serial interface of R1 is 790. Yes, re-read 790. Delay is read in tens of microseconds. So, by setting up 790, you would receive a ratio of 5:2 now.
I haven't added any screenshots of the configs as it's left to you to perform it :-D Oh ya, even 4:3 calculation is left to you for practice !!!!
1) Path via R2 is the preferred path currently as the Delay parameters are least.
2) Path via R3 is the feasible successor because the Relative distance advertised by R3 to R1 is the same as advertised by R2 to R1. (i.e 100 + 5000 = 5100)
What is that we can do in order for path via R3 to be used for load balancing? To achieve this, we need to use EIGRP variance feature. Lets calculate the metric to reach R4's loopback from R1 manually. Below is the formula
Metric = 256 * (Sum of Delay/10)
Note : Delay is in tens of microseconds
Metric via R2 is = 256 * (100+100+5000)/10 = 133120
Metric via R3 is = 256 * (20000 + 100 + 5000) = 642560
So, we know that Metric via R2 will be the preferred path of the least Feasible distance. So, lets use our R3 path as well.
Remember, Variance = FD of the Feasible successor / FD of the successor
So, Variance = 642560/133120 = 4.82
Lets round that up to a whole number. So, Variance = 5
Now, by setting variance 5 under the EIGRP routing process, you would have the load balancing between two paths up.
Note : For the variance command to take effect, the path must be a feasible successor
But how to achieve 5:2 or 4:3 ratio load balancing? For this to happen, you need to consider the below things
1) How much delay should be set on the path via R3(the serial interface path) in order to get 5:2 ratio?
2) What would be the calculation to obtain the delay value?
To calculate the delay, below is the formula
Lowest Metric * = 256 * [delay/10]
* Lowest Metric is the path with the lowest feasible distance (in our case path via R2)
133120 * (5/2) = 256 * [delay]/10
332800 = 256 * [delay/10]
332800/256 = delay/10
1300=delay/10
13000=delay
Maths :)
The above delay value we calculated is the delay of the entire path (end-to-end). Now, we need to determine the delay value of the local interface. To find that, you need to subtract the advertised delay received from R3.
So, it would be 13000-5100 = 7900
The actual delay to be set on the serial interface of R1 is 790. Yes, re-read 790. Delay is read in tens of microseconds. So, by setting up 790, you would receive a ratio of 5:2 now.
I haven't added any screenshots of the configs as it's left to you to perform it :-D Oh ya, even 4:3 calculation is left to you for practice !!!!
