Understanding the EIGRP command, “metric rib-scale”
You may recall that, when using Named-Mode EIGRP configuration you have automatic access to EIGRP Wide Metrics. In addition to providing you a new K-Value (K6 which is used against Jitter and Energy) the EIGRP Distance formula has been revised (what they call, “scaled”) to account for links above-and-beyond 10Mbps. Remember that with Classic-Mode EIGRP, the formula looked like this:
metric = ([K1 * bandwidth + (K2 * bandwidth) / (256 - load) + K3 * delay] * [K5 / (reliability + K4)]) * 256
In the formula, the “**bandwidth**” value was represented as:
BW = 10^7 / minimum BW
The problem with this “classic” method was that any link with a bandwidth higher than 10,000,000 bps (which only equates to 10Mbps, or 10^7 bps) was given the same BW value as an Ethernet segment. In other words, whether you put Ethernet into that formula, FastEthernet, Gigabit Ethernet, or anything even higher…they all equate to “1″. So in Classic Mode EIGRP, EIGRP couldn’t distinguish between these types of links to develop an accurate path to a destination.
When EIGRP Wide-Metrics were developed, Cisco “scaled” some portions of the formula to account for faster links (as Continue reading