[c-nsp] EIGRP metric and MTU

[Oliver Boehmer (oboehmer)]

Alex Semenyaka <> wrote on Saturday, March 04, 2006 3:23 PM:

> Collegues,
> 
> I've a little bit confused. A lot of sources (from textbooks to Cisco
> Tac Case http://www.ciscotaccc.com/iprout/showcase?case=K10340813)
> say that EIGRP composite metric takes into account bandwidth, delay,
> load, reliability and MTU. While all is clear with the first four
> (well-known expression for EIGRP metric lists them all), the role of
> MTU is absolutely unclear. I failed to find any source describing the
> way MTU could influence the composite metric. Moreover, the document
>
http://www.cisco.com/en/US/customer/tech/tk365/technologies_white_paper0
9186a0080094cb7.shtm
> (to which the mentioned TAC Case referred) says about MTU in the
> metric context only 
> 
> Minimum MTU is 1500 	This field is not used in metric calculations.
> 
> That differs from the description for load and reliability, those are
> "not used BY DEFAULT" (so, could be used, if K2 and K5 will not be 0).
> 
> Could anyboudy make clear, does MTU and EIGRP metric really connected?
> And if so, then how?

The Minimum MTU is carried within advertisements, but it is never used
in the composite metric calculation. I agree, this should be cleaned up
as this is referenced in several places.

	oli