MTU isn't part of the IGRP or EIGRP metric. In other words, it's not used when selecting which route is better. Although not used as part of the metric, an EIGRP router does forward MTU info to other routers and keep track of an MTU for each route. MTU is the maximum packet size that can be sent along the entire path without fragmentation. (That is, it is the minimum of the MTUs of all the networks involved in the path.)
So, when doing redistribution of a route learned by some other routing protocol, you have to tell the EIGRP process info on the MTU so it knows what to use. You have to feed EIGRP the info it will carry in EIGRP route updates for this redistributed route: bandwidth, delay, reliability, load, and MTU. By the way, EIGRP also carries a hop count. It's not used for the metric either, and you don't have to feed it into EIGRP when redistribution. I guess EIGRP figures it out. Hop count is just used to avoid loops. If the router sees it increasing, it puts the route in holddown. Priscilla At 09:18 PM 4/20/02, Michael L. Williams wrote: >So I'm just trying to make sure that I'm not losing it. > >According to Cisco, the metric calculation for IGRP is (EIGRP being the same >except times 256): > >(K1*Bw) + (K2*Bw)/(256-Load) + (K3*Delay)*(K5/(Reliability + K4)) > >But then other stuff I've read says that (E)IGRP metric is calculated using >Bandwidth, Load, Reliability, Delay, and MTU. For instance to set a default >metric the command is: > >default-metric > >Cisco has a page on redistribution that says: > >"IGRP and EIGRP need five metrics when redistributing other protocols: >bandwidth, delay, reliability, load and maximum transmission unit (MTU) >respectively." > >So according to the formula above, where does MTU come into play?!?!?!? Am >I missing something?!?!? If MTU isn't part of the metric calculation, why >bother putting it in when setting default metrics or redistributing other >protocols into (E)IGRP? > >I know this is a pretty "basic" question, but I was just reviewing some >stuff and came across this. > >Mike W. ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=42109&t=42103 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
