From: Enrique Langmaack (langmaack@gmail.com)
Date: Wed Apr 16 2008 - 19:59:51 ART
Mike, if I reenable keepalives and set the errdisable recovery mechanism the
interfaces begin to flap. I have also doublechecked that I don't have any
loopguad mechanism enabled.
Once again when I disable keepalives on the interfaces, they stop the
flapping behaviour.
Also, this seems now to happen only with mst, when I set everything to pvst
with keepalives enabled I don't get this issue.
Thanks
On Wed, Apr 16, 2008 at 2:34 PM, Mike Harrison <michael.h4@blueyonder.co.uk>
wrote:
> Enrique
>
> Looks like you have something else going on - I have found loopback errors
> usually occur when you telco loops a circuit to test it on a metro ethernet
> connection or the like. The switch sees a physical loop between tx and rx of
> the port - not to be confused with stp loops.
>
> You can set the switch to auto recover from the err disable - something
> like;
>
> errdisable recovery cause loopback
> errdisable recovery interval 30
>
> Not sure why this would error in a lab situation though?
>
> Mike
>
> ----- Original Message ----- From: "Enrique Langmaack" <
> langmaack@gmail.com>
> To: <ccielab@groupstudy.com>
> Sent: Wednesday, April 16, 2008 8:05 PM
> Subject: loopback err-disable on switches
>
>
> Hi,
> >
> > While I have been doing some labs with pvst and mst using four switches
> > and
> > been connected forming physical loops, I was not able to have all of the
> > trunks between the ports of these switches either in a fwd or blk state.
> > I
> > always got at least a couple of ports somewhere in the topology in the
> > err-disable state.
> >
> > Everytime this happened, switches showed something like this:
> >
> > %PM-4-ERR_DISABLE: loopback error detected on Fa0/20, putting Fa0/20 in
> > err-disable state
> >
> > So by searching this on cisco documentation I found the following:
> >
> >
> > "A loopback error occurs when the keepalive packet is looped back to the
> > port that sent the keepalive. The switch sends keepalives out all the
> > interfaces by default. A device can loop the packets back to the source
> > interface, which usually occurs because there is a logical loop in the
> > network that the spanning tree has not blocked. The source interface
> > receives the keepalive packet that it sent out, and the switch disables
> > the
> > interface (errdisable). This message occurs because the keepalive packet
> > is
> > looped back to the port that sent the keepalive:
> >
> > %PM-4-ERR_DISABLE: loopback error detected on Gi4/1, putting Gi4/1 in
> > err-disable state"
> >
> > (
> >
> > http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00806cd87b.shtml
> > )
> >
> > So basically what I did is disabling keepalives on trunk interfaces on
> > my
> > switches so now I don't fall into this issue.
> >
> > However I was wondering if this workaround would impact on anything else
> > or
> > would be allowed during the real ccie lab.
> >
> > Thanks for your help
> >
> >
> > Pass the CCIE in six weeks, Guaranteed!
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