In Eigrp I know that the following contributes the Metric
I trying to understand how MTU influence the Metric. It labbed it. R1 (ser
0/0) ----(ser 0/0) R2
I changed the metric of R1 ser 0/0 to 1200 and noticed the Metric value
didn't change. How and when MTU comes into play.
Also I noticed the Eigrp messages donot contain MTU details.
Can you pl give your valuable time and help us
this is a good question.
MTU is not part of the composite metric. However, EIGRP routes both internal and external are carried within TLV data structures.
The TLV is oriented at providing in multiple fields data ready for EIGRP calculation of local node that is:
minimum BW on path
cumulated delay on path
minimum MTU on path
number of router hops
you can see this information using sh ip eigrp topology
the local node to calculate the metric from its own point of view just needs to:
add the delay of its own interface where the update has been received
to verify the bandwidth parameter of its own interface where the update has been received if its higher of current minimum BW this field is left unchanged.
to add 1 to router hop field
to verify the MTU parameter of its own interface where the update has been received if its higher of current minimum MTU this field is left unchanged.
MTU and number of router hops are used as tie breakers in case of paths with equal EIGRP metric, the path with the highest minimum MTU is preferred as well as the path with the minimum router hop count.
to be noted that delay already provides a measure of hop count weighted with delay of each link in the path.
Hope to help