Understanding EIGRP Metric Coefficients (K-Values)

EIGRP (Enhanced Interior Gateway Routing Protocol) utilizes metric coefficients, often referred to as K-values or vector metrics, to calculate the composite metric for route selection. In RFC 7868: Section 5.5, we explore these coefficients and their significance in EIGRP routing.

Metric Coefficients (K-Values):

• Metric coefficients, represented as K-values, play a crucial role in EIGRP's metric calculation. Each K-value corresponds to a specific metric component:
  • K1 = 1: Represents Bandwidth
  • K2 = 0: Denotes Load
  • K3 = 1: Corresponds to Delay
  • K4 = 0: Signifies Reliability
  • K5 = 0: Also Reliability

Important Note - MTU:

• It's important to clarify that the Maximum Transmission Unit (MTU) is not considered a K-value in EIGRP. Additionally, MTU is not used in any way when calculating the composite metric.

Units of Measure:

• The units of measure for key metrics are as follows:
  • Bandwidth (BW) is in Kilobits per second (Kbps).
  • Delay (DELAY) is in tens of microseconds.

Composite Metric Calculation:

The composite metric equation, with default K-values, is as follows:

• BW is calculated as (10^7 / BW in Kbps).
• DELAY is divided by 10 to represent tens of microseconds.
• Multiplying by 256 ensures a 32-bit metric, as IGRP used a 24-bit metric, and this adjustment provides increased granularity.

Selection of BW/K1 and DELAY/K3 Values:

• The following guidelines dictate which BW/K1 and DELAY/K3 values are used:
  • BW/K1 corresponds to the slowest outgoing link speed toward the destination.
  • DELAY/K3 represents the cumulative delay of all outgoing interfaces toward the destination.

K-Values Consistency:

• It is essential that K-values match between neighboring routers. If they do not match, neighbor adjacency will not form. If an adjacency is established with matching K-values and they are subsequently changed to be inconsistent, the adjacency will terminate.

Manipulating Prefixes with K-Values:

• EIGRP does not allow manipulation of individual prefixes using K-values. It's an all-or-nothing approach for routing decisions.

Verification Commands:

To verify and fine-tune EIGRP metric calculations, use the following commands:

• metric weights [tos] k1 k2 k3 k4 k5: Adjust K-values to influence metric calculations.
• delay [tens of microseconds]: Configure delays in tens of microseconds.
• show ip eigrp topology x.x.x.x: Display the EIGRP topology for specific routes.
• offset-list [acl] [in/out] [offset value] [interface]: Apply offset lists to manipulate metrics for route selection.

In summary, comprehending EIGRP metric coefficients and their impact on route selection is pivotal for network administrators. Proper configuration and consistency of K-values, along with fine-tuning options, allow for optimized routing decisions within an EIGRP network.