EIGRP Wide Metrics

EIGRP uses the bandwidth, delay, reliability, load and K values to calculate a composite cost metric. The problem with this metric is that it doesn’t scale for high bandwidth interfaces. The composite cost metric is calculated like this:

EIGRP composite cost metric = 256*((K1*Scaled Bandwidth) + (K2*Scaled Bandwidth)/(256 – Load) + (K3*Scaled Delay)*(K5/(Reliability + K4)))

In the formula above, you can see that the bandwidth is scaled. It’s done with the following formula:

Scaled bandwidth = (107/minimum bandwidth (Bw) in kilobits per second)

The delay is also scaled, using this formula:

Scaled Delay = (Delay/10)

By default, only K1 and K3 are enabled, only bandwidth and delay are used. This means the composite cost metric can be simplified to the following formula:

EIGRP composite cost metric = 256*(Scaled Bandwidth + Scaled Delay)

The scaled bandwidth formula is unable to differentiate between anything faster than 10 GigabitEthernet. The lowest delay that we can configure is 10 microseconds, that’s the delay GigabitEthernet interfaces offer. Anything above GigabitEthernet will also have a delay of 10 microseconds.

Here are some examples to help you understand this:

  • GigabitEthernet:
    • Scaled bandwidth: 10000000 / 1000000 = 10
    • Scaled delay: 10 / 10 = 1
    • Composite metric: 10 + 1 * 256 = 2816
  • 10 GigabitEthernet:
    • Scaled bandwidth: 10000000 / 10000000 = 1
    • Scaled delay: 10 / 10 = 1
    • Composite metric: 1 + 1 * 256 = 512
  • 11 GigabitEthernet:
    • Scaled bandwidth: 10000000 / 11000000 = 0.9 (rounded to 0)
    • Scaled delay: 10 / 10 = 1
    • Composite metric: 0 + 1 * 256 = 256
  • 20 GigabitEthernet:
    • Scaled bandwidth: 10000000 / 20000000 = 0.5 (rounded to 0)
    • Scaled delay: 10 / 10 = 1
    • Composite metric: 0 + 1 * 256 = 256
  • 40 GigabitEthernet:
    • Scaled bandwidth: 10000000 / 40000000 = 0.25 (rounded to 0)
    • Scaled delay: 10 / 10 = 1
    • Composite metric: 0 + 1 * 256 = 256

Above, you can see that the scaled bandwidth of anything higher than 10 GigabitEthernet has a value that is below one and is rounded down to zero. The delay has a value of one for GigabitEthernet or faster interfaces.

Any interface above 10 GigabitEthernet will always have a composite cost metric of 256. To EIGRP, there is no difference between anything above 10 GigabitEthernet or 40 GigabitEthernet interfaces and this might cause undesirable equal-cost load balancing in your network.

The metric and its formulas as explained above is called the EIGRP classic metrics. To solve this problem, EIGRP supports wide metrics which uses 64-bit values instead of the 32-bit values that EIGRP classics metric uses. EIGRP wide metrics supports interfaces up to 4.2 terabits and uses a different composite cost metric formula. It has the following components:

  • Throughput: this is the bandwidth, it uses a new scaled bandwidth formula.
  • Latency: this is the delay, in picoseconds. 1000000000 picoseconds = 1 millisecond. It also uses a new latency scaling formula.
  • Reliability: the same as with EIGRP classic metrics.
  • Load: the same as with EIGRP classic metrics.
  • MTU: the same as with EIGRP classic metrics.
  • Hop Count: the same as with EIGRP classic metrics.
  • Extended Metrics: these are currently not used but reserved for future extensions. There are three extended metrics as of this moment:
    • Jitter
    • Energy
    • Quiescent Energy

To add these extended metrics to the composite metric, a new K value was introduced called K6.

Let’s take a look at the wide metrics composite metric formula:

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Forum Replies

  1. Hi William,

    Under topology base you will find commands that have to do with the EIGRP topology table. Stuff like redistribution, filtering, etc. Here’s an overview of all commands:

    R1(config-router)#router eigrp TEST                               
    R1(config-router)#address-family ipv4 unicast autonomous-system 1 
    R1(config-router-af)#topology base                                  
    R1(config-router-af-topology)#?
    Address Family Topology configuration commands:
      auto-summary         Enable automatic network number summarization
      cts                  EIGRP Trust
    ... Continue reading in our forum

  2. Hi Lagapides ,

    Thanks …Well understand this explanation…

  3. Hello Vinod

    The main differences between named and classic modes are the way in which they are implemented (globally for named while both globally and in interface mode for classic) as well as the addition of a sixth K value for the metric.

    On the back end, that is, concerning the way that the routers interpret and operate in EIGRP, very little has changed. So a named mode EIGRP router can communicate with a classic EIGRP router. Since you configure the AS number under the EIGRP name configuration, if the AS is the same, they will communicate.

    Now the only re

    ... Continue reading in our forum

  4. Hello Network

    EIGRP named mode supports what is known as the Wide Metrics feature. This feature supports 64-bit metric calculations as opposed to EIGRP classic mode that use 32-bit calculations. This results in varying metric values between the two.

    Wide metrics was introduced in order to accommodate high-bandwidth interfaces and Ethernet channels. The increase in available speeds has resulted in incorrect or inconsistent routing behavior with the classic EIGRP routing metrics. The lowest delay that can be configured for an interface is 10 microseconds. As a

    ... Continue reading in our forum

  5. Hi Rene and staff

    i just look at EIGRP named to configure a lab in another lesson
    So i explore the commands of the configuration modes; in the labs i did, i only used the topology mode base

    //cdn-forum.networklessons.com/uploads/default/original/2X/8/87a71f721e6599edd2950c22c1f353b41646ecbf.jpeg

    I tried to test (just for fun) the command with EIGRP that i suppose to set Multi-Topology Routing

    //cdn-forum.networklessons.com/uploads/default/original/2X/c/caea5318bdc479a90f5e217502cbdd6967531566.jpeg

    As you see, IOS answer “VIDEO does not exist”
    Could you give me

    ... Continue reading in our forum

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