EIGRP metrics----load and reliability

[2pparish]

I'm trying to find a good explanation of EIGRP metrics, load and reliability.

I know the default values

load = 1 or 1/255

and

reliability 255 or 255/255

but what does all of this mean?

[Richard Burts]

Paul

In the early discussion of the metrics it was deemed interesting and potentially useful to incorporate into the metric factors that represented reliability of the link (more reliable link is good and less reliable link is not good) and load (lightly loaded link should be more utilized and heavily loaded link should not). However as they gained experience with the protocol that these factors were not so useful after all. The specification of the metric includes these factors, but the default of the k values used in the calculation of the metric specifies that neither of these factors is actually used in the calculation.

HTH

Rick

[kerek]

Hi,

In addition to Rick's post not just the inefficiency can be the problem but also a increased number of routing updates caused by the changing load.

Krisztian

[2pparish]

What I'm looking for is a good explanation of load and reliability.

For example: Delay, which is one of the metrics is often misunderstood.

Delay represents the "end to end" delay which incorporates multiple types of delay, which include serialization delay, propogation delay, and queuing delay.

I need a good definition and explanation of load and reliability.

Thanks

Paul

[mohammedmahmoud]

Hi,

Rick, i think that i've also read once that since both Load (depending on the interface utilization) and Reliability (depending on CRCs and so on the interface) are dynamic, thats why they are not desired to be used in the metric as they can led into unpredictable path selection, and thats behind the reason of neglecting them by default in the calculation, what do you think about this.

HTH,

Mohammed Mahmoud.

[Richard Burts]

Mohammed

Yes the dynamic nature of both load and reliability is the major reason why they turned out to be not useful and by default are neglected in the calculation. I thought about going into this in my original post and decided to keep it more simple and direct response. But to provide additional depth in the answer you are correct that the dynamic nature of load and reliability would bring instability into the routing table.

HTH

Rick

[mohammedmahmoud]

Rick,

Thanks a lot for your professional feedback :)

Its really nice having you as a reference in the forum.

BR,

Mohammed Mahmoud.

[dino.demarco]

If they other replies have not satisfied your question, perhaps you are looking to understand the numbers???

If so, these numbers (x/255) are a ratio that express the level of load or reliability for a given link. 1/255 equates to ~0% and 255/255 equates to 100%. So, if you were using load to calculate the metric, and the load for a given link was determined to be 240/255 (or ~94%), this would increase the metric making it a less desirable choice.

I hope this helps.