This topic very accurately describes how the wide metric calculation works (and boy, is there a lot of bullshit on the web about this calculation with wide metrics). Below is a simple topology to demonstrate how the EIGRP wide metrics work.
EIGRP-WIDE-METRICS
Below is the current configuration of each router. Simply put, a very basic EIGRP name mode config has been put on all three devices. This lab will be using default K values.
R9#sh run | s eigrp
router eigrp A
!
address-family ipv4 unicast autonomous-system 1
!
topology base
exit-af-topology
network 155.1.79.0 0.0.0.255
exit-address-family
R7#sh ru | s eigrp
router eigrp A
!
address-family ipv4 unicast autonomous-system 1
!
topology base
exit-af-topology
network 155.1.67.0 0.0.0.255
network 155.1.79.0 0.0.0.255
exit-address-family
R6#sh run | s eigrp
router eigrp A
!
address-family ipv4 unicast autonomous-system 1
!
topology base
exit-af-topology
network 155.1.67.0 0.0.0.255
exit-address-family
In this example, we will look at R9 for the route 155.1.67.0/24, and work out how the metric was calculated.
R9#sh ip eigrp topology 155.1.67.0/24
EIGRP-IPv4 VR(A) Topology Entry for AS(1)/ID(150.1.9.9) for 155.1.67.0/24
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 1966080, RIB is 15360
Descriptor Blocks:
155.1.79.7 (GigabitEthernet1.79), from 155.1.79.7, Send flag is 0x0
Composite metric is (1966080/1310720), route is Internal
Vector metric:
Minimum bandwidth is 1000000 Kbit
Total delay is 20000000 picoseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 1
Originating router is 150.1.7.7
Explination of the forumla
Its essentially Throughout + Latency. Where previously in classic EIGRP it was BW + Delay. They are effectively the same thing in the calculation, but just renamed. The forumla breaks down into the following
Throughput = 65536 * 10^7 / minimum bandwidth across all links in the path
Latency = 65536 * total delay (in picoseconds) / 10^6
Composite metric = Throughput + Latency
Important Notes:
65536 is a constant value that never changes, known as the Wide-Scale-Constant. Note: this is not the RIB-Scale.
10^7 is a constant value, i.e. it is always 10^7. Cisco names this EIGRP_BANDWIDTH in the documentation.
10^6 is a constant value, i.e. it is always 10^6. Cisco names this EIGRP_DELAY_PICO in the documentation.
EIGRP wide metric calculation of the prefix 155.1.67.0/24
Using what we know from breaking down the formula (above) the calculation for my prefix of 155.1.67.0/24 is as follows:
Throughout = 65536*10^7/1000000 = 655360
Latency = 65536*20000000/10^6 = 1310720
Composite metric = 655360 + 1310720 = 1966080
As you can see its a perfect match.