The first condition is used in either unequal OR equal cost load balancing. It is to
prevent routing loops. Think of it like this: Let's say I'm going on vacation. I'm
in Arizona. I want to get to Florida. I can go thru Texas, which is my best route,
and there is a certain distance from California to Florida. If I can't get thru Texas
becauuse all the roads are closed. My options are to go thru Kansas or California.
Kansas is closer to Florida than Arizona, so it fits the rules & I will consider it.
California is further from Florida than Arizona is, so I won't consider it. If I went
thru California, once I got there the gas station attendant would tell me to go thru
Arizona, and I would drive in a loop forever.
Notice this is comparing total distance of best route (from source to destination)
with advertised distance of alternate routes (from next hop to destination).
The second condition is how much difference in total distances should I tolerate.
Same analogy as above - If I am doing equal cost load balancing, The total distance
from Arizona - Texas - Florida is shorter than from Arizona - Kansas - Florida, so I
and my buddy will both drive thru texas. If I am doing unequal cost, the variance
tells me how much different the alternatives can be from the best (as a multiple of
the best).
Notice here we are comparing total distance of the best router to total distance of
alternate routes.
Now the only thing beyond that is to remember that unlike in driving, the hop-by-hop
metrics in EIGRP are not calculated ina totally additive fashion - rather it's lowest
bandwidth on a link in the path (which is not additive) plus total delay (which is
additive).
>>> Helena <[EMAIL PROTECTED]> 09/12 12:46 AM >>>
Hi everyone,
CAn someone please explain the two feasibility conditions in EIGRP
unequal-cost load balancing?
They are:
- local best metric > best metric learned from the next router
- the "multiplier" x Local bestmetric for the destination > metric through
the next router
Thanks in advance
Helen
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