Re: EIGRP Neighbors Flapping b/c of mismatch MTU ?

From: Pavel Bykov (slidersv@gmail.com)
Date: Sun Feb 15 2009 - 18:47:21 ARST

That does not sound too logical... The only case that pops into mind that
due to inconsistent MTU updates got lost too many times, so one of the side
reset connection using graceful shutdown or restart which basically is an
EIGRP hello message with all K values set to 255.
In new IOS this appears as "graceful shutdown", in older ones it appears as
"K-Value mismatch"

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6554/ps6599/ps6630/prod_presentation0900aecd80310eff.pdf

On Sun, Feb 15, 2009 at 8:12 PM, Hussam EL Kebbi <hussamkibbi@hotmail.com>wrote:

> Topology: Hub and spoke (Frame Relay).
>
>
>
> When changed MTU to 2100 on spokes, it started flapping (with K value
> mismatch
> message).
>
> When changed them back to 1500 as they are with hub, everything worked
> fine.
>
>
>
> Date: Sun, 15 Feb 2009 10:33:22 -0800
> Subject: Re: EIGRP Neighbors Flapping b/c of mismatch MTU ?
> From: narbikk@gmail.com
> To: salah.elshekeil@gmail.com
> CC: hussamkibbi@hotmail.com; all.from.nj@gmail.com; ccielab@groupstudy.com
>
> What is the topology?
>
>
>
> On Sun, Feb 15, 2009 at 10:23 AM, Salahaddin Elshekeil
> <salah.elshekeil@gmail.com> wrote:
>
> EIGRP Neighbor Problem Cause: Mismatched K Values
> For EIGRP to establish its neighbors, the K constant value to manipulate
> the
> EIGRP metric must be the same. In EIGRP's metric calculation, the default
> for the K value is set so that only the bandwidth and the delay of the
> interface are used to calculate the EIGRP metric. Many times, the network
> administrator might want other interface factors, such as load and
> reliability, to determine the EIGRP metric. Therefore, the K values are
> changed. Because only bandwidth and delay are used in calculations, the
> remaining K values are set to a value of 0 by default. However, the K
> values
> must be the same for all the routers, or EIGRP won't establish a neighbor
> relationship.
>
> example: K1 is bandwidth and K3 is delay. when you change the K values
> of Router B to all 1s from K1 to K4, while Router A retains the default
> value of K1 and K3 to be 1. In this example, Router A and Router B will not
> form EIGRP neighbor relationship because the K values don't match
>
> Router A------------------ Router B
>
> to change the K values
>
> use this command under the eigrp process "*metric weights* *tos k1 k2 k3 k4
> k5 * "
>
> Default values:
>
> *tos**: *0
>
> *k1**:** *1
>
> *k2**:* 0
>
> *k3**:* 1
>
> *k4**:* 0
>
> *k5**:* 0
>
> the metrics between the two routers should be matched so they can form
> neighbor relationship
>
>
> On Sun, Feb 15, 2009 at 8:52 PM, Hussam EL Kebbi
>
>
>
> <hussamkibbi@hotmail.com>wrote:
>
> > Actually I was working on real network environment that I don't have
> access
> > now anymore.
> >
> >
> >
> > I am only surprised that nothing worked when neighbors were flapping
> unless
> > when I put MTU equal to each others!!!
> >
> >
> >
> > Does it have to do with LMI can't be fragmented or something? any idea?
> >
> >
> >
> > The output error was (K-values mismtach).
> >
> >
> >
> > > Date: Sun, 15 Feb 2009 10:44:12 -0500
> > > Subject: Re: EIGRP Neighbors Flapping b/c of mismatch MTU ?
> > > From: all.from.nj@gmail.com
> > > To: hussamkibbi@hotmail.com
> > > CC: ccielab@groupstudy.com
> > >
> > > A quick lab test:
> > >
> > > %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 1.1.1.1 (Serial0/0.1) is
> > down:
> > > Insufficient MTU
> > >
> > > R3(config-if)#do sho debug
> > > IP routing:
> > > IP-EIGRP Neighbor Target Events debugging is on
> > > IP-EIGRP Route Events debugging is on
> > >
> > > I get this message when I tune the MTU to a very low value, but I was
> not
> > > able to get it when the MTU were only slightly different.
> > >
> > > Have you progressed through the lab to a point where other configs have
> > > caused problems? For EIGRP, slightly different MTU sizes should not
> > matter
> > > much in the lab type environment.
> > >
> > > Any additional insight to what your configs look like might help / be
> fun
> > > for those of us wanting to lab test this along with you. I will be out
> > for
> > > most of the day ... going snowboarding! ;-)
> > >
> > > andrew>
> > > andrew>en
> > > andrew#
> > > andrew# config brain
> > > andrew(wacky brain)# go snowboarding today
> > >
> > > Andrew Lee Lissitz
> > >
> > >
> > >
> > > On Sun, Feb 15, 2009 at 5:17 AM, Hussam EL Kebbi
> > <hussamkibbi@hotmail.com>wrote:
> > >
> > > > Hi Experts,
> > > >
> > > >
> > > >
> > > > I was working on a lab (EIGRP over Frame Relay) and I noticed that
> when
> > MTU
> > > > is
> > > > different between neighbors
> > > >
> > > > it starts flapping, but when I changed MTU to same on both neighbor
> > > > interfaces, it works just fine.
> > > >
> > > >
> > > >
> > > > Any idea why?
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > Thank You,
> > > >
> > > > Hussam
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > _________________________________________________________________
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> > > >
> > >
> > >
> > > --
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> > > all.from.nj@gmail.com
> > >
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-- 
Pavel Bykov
----------------
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