Configuration Guide: EIGRP Wide Metrics

From: IP Routing: EIGRP Configuration Guide, Cisco IOS Release 15M&T

  • The EIGRP Wide Metrics feature supports 64-bit metric calculations and Routing Information Base (RIB) scaling in Enhanced Interior Gateway Routing Protocol (EIGRP) topologies. 
  • The 64-bit calculations work only in EIGRP named mode configurations. EIGRP classic mode configurations use 32-bit calculations.
  • EIGRP monitors metric weights, by using K values, on an interface to allow the tuning of EIGRP metric calculations and to indicate the type of service (ToS). K values are integers from 0 to 128; these integers, in conjunction with variables like bandwidth and delay, are used to calculate the overall EIGRP composite cost metric.
  • Although you can configure K values to produce varying routing behaviors, most configurations use only the delay and bandwidth metrics by default, with bandwidth taking precedence, to produce a single 32-bit metric. Use of the default constants effectively reduces the above-mentioned composite cost metric formula to the following default formula: 256*(Scaled Bw + Scaled Delay).
  • For example, let us consider a link whose bandwidth to a particular destination is 128 kb/s and the delay is 84,000 microseconds. By using the default formula, you can simplify the EIGRP composite cost metric calculation to 256*(Scaled Bw + Scaled Delay), thus resulting in the following value: Metric = 256*(107/128 + 84000/10) = 256*86525 = 22150400
  • The Enhanced Interior Gateway Routing Protocol (EIGRP) composite cost metric (calculated using the bandwidth, delay, reliability, load, and K values) is not scaled correctly for high-bandwidth interfaces or Ethernet channels, resulting in incorrect or inconsistent routing behavior. 
  • The lowest delay that can be configured for an interface is 10 microseconds. As a result, high-speed interfaces, such as 10 Gigabit Ethernet (GE) interfaces, or high-speed interfaces channeled together (GE ether channel) will appear to EIGRP as a single GE interface.
  • To resolve this issue, the EIGRP Wide Metrics feature supports 64-bit metric calculations and Routing Information Base (RIB) scaling that provide the ability to support interfaces (either directly or via channeling techniques like port channels or ether channels) up to approximately 4.2 terabits.
  • To accommodate interfaces with bandwidths above 1 gigabit and up to 4.2 terabits and to allow EIGRP to perform path selections, the EIGRP composite cost metric formula is modified.
  • The time that information takes to travel through links is measured in picoseconds.
  • Metric = [(K1*Minimum Throughput + {K2*Minimum Throughput} / 256-Load) + (K3*Total Latency) + (K6*Extended Attributes)]* [K5/(K4 + Reliability)]
  • Default K values are as follows:
    • K1 = K3 = 1
    • K2 = K4 = K5 = 0
    • K6 = 0
  • The EIGRP Wide Metrics feature also introduces K6 as an additional K value for future use.
  • By default, the path selection scheme used by EIGRP is a combination of throughput (rate of data transfer) and latency (time taken for data transfer), and the formula for calculating the composite cost metric is as follows:
  • Composite Cost Metric = (K1*Minimum Throughput) + (K3*Total Latency)
  • Minimum Throughput = (10^7 * 65536)/Bw), where 65536 is the wide-scale constant.
  • Total Latency for bandwidths below 1 gigabit = (Delay*65536)/10, where 65536 is the wide-scale constant.
  • Total Latency for bandwidths above 1 gigabit = (10^7 * 65536/10)/ Bw, 65536 is the wide-scale constant.
  • With the calculation of larger bandwidths, EIGRP can no longer fit the computed metric into a 4-byte unsigned long value that is needed by the Cisco RIB. To set the RIB scaling factor for EIGRP, use the metric rib-scale command. When you configure the metric rib-scale command, all EIGRP routes in the RIB are cleared and replaced with the new metric values.
  • The K values are changed using the metric weights command. 

Device-B(config)# router eigrp NAME1
Device-B(config-router)# address-family ipv4 autonomous-system 4533
Device-B(config-router-af)# network
Device-B(config-router-af)# metric weights 0 1 0 1 0 0 0


  1. After a long time, I read a very beautiful and very important article that I enjoyed reading. I have found that this article has many important points, I sincerely thank the admin of this website for sharing it. Best eigrp service provider.


Post a Comment