Sometimes we have to pay attention to little details
Just take a look on EIGRP Metrics
EIGRP have a composite metric based on multiples elements: Bandwidth, Delay, Mtu, Load, Reliability.
Bandwidth is the least bandwidth encountered on the path to the router (in bps)
Delay is the cumulative delay of all the links encountered on the path to the router (in 1/10s)
Mtu is the maximum transfer unit as we already know
Load is the load of the interface were packet arrived
Reliability
If we want to see these infos, we just have to type: show ip interfaces Fa0/0 or on any interface participating in EIGRP.
All these parameters are subject to a factor by which they can be multiplied in order to obtain the metric; these parameters are the K values.
We have one key value par element from K1 to K5
Let's remember us the original formula of EIGRP metric : Metric = 256*([K1*Bw + K2*Bw/(256-Load) + K3*Delay]*[K5/(Reliability + K4)])
EIGRP original metric formula is quite a bit very difficult to have it by mind, thanks God the default K values in Cisco IOS are K1=1, K2=0, K3=1, K4=0 and K5=0. After applying these K values to the precedent formula we have now
Metric = 256*(10^7/Bw)+(256*Delay), by default our Cisco routers use only Bandwidth and Delay for EIGRP metric
Just to keep in our mind 2 things:
1/ metric weight command in EIGRP
Ex: metric weight 1500 15 150 255 12 // instruct the router to use these values as the new K values instead of 1 0 1 0 0, we just change the multiplier
The element of the metric will be used based on values obtain by the routing protocol itself
In fine we will have Metric = 256*([1500*Bw + 15*Bw/(256-Load) + 150*Delay]*[12/(Reliability + 255)])
2/ redistribute command in EIGRP
Ex: redistribute ospf 1 1500 15 150 255 12 // instruct the router to redistribute OSPF and use for those OSPF routes these elements values (not K values with this command the K values will be left to their default)
Here 1500 = bandwidth metric / 15 = delay metric / 150 = reliability metric / 255 = loading metric / 12 = mtu metric
In fine we will have Metric = 256*([K1*1500 + K2*1500/(256-255) + K3*15]*[K5/(150 + K4)])
PS: I have only received my book (CCIE Routing and Switch Certification Guide 4th Edition) today June 20th while on Amazon.com they told me May 25th
